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Tea Quality

Introduction

The need to understand the chemistryof tea manufacture was underscored in theearly 1950s when the Tea ResearchInstitute of East Africa was established1.The history of early work is presented in

the following sections.The tea research problems were

outlined by Eden in 19542 and hespeculated on the morphological basis oftea quality3. The speculations formed the

basis of further experiments. However,greatest effort has been put intoinvestigations of the chemical aspects oftea quality.

Chemical and biochemicalaspects of tea quality

Chemistry of fresh leaves

It was recognised that it is necessary toquantify the total polyphenol content and

polyphenol oxidase activity in the leaf asthis could be related to liquor properties ofresultant black teas4. The yield of dryenzyme powder from 10 g of fresh leaf

was 1.3 g to 1.4 g (13419). Totaloxidisable matter had little seasonalvariation while enzyme activity fluctuatedmore with time of the year5. The accuracyof the measurements of the parameterswas however less certain. During theSecond Tea Research Institute of EastAfrica conference, a lecture was also givenon the chemistry of the tea leaf in relationto manufacture6. However earlytechniques for processing tea were

summarised by Hainsworth in 1969

7

.

Parameters of processed tea quality

Attempts were made to associate thechemical parameters of tea to taste8. Thesestudies revealed that the stimulating actionof tea was due to caffeine and the strengthand quality of the copper colour due to theoxidation of the catechins to theaflavin and

thearubigin. Both theaflavin andthearubigin form complexes with caffeineand protein which together with thearomatic compounds define the characterof tea.

Theaflavins

Quality is normally subjectivelydescribed by the tea trade. Producersdefine quality tea as that whose sale leadsto higher income. Tea traders define

quality tea as that which gives maximumprofit, while consumers define quality teaas one with overall taste and class.Research prompted by the requirement ofthe tea trade has been conducted to definechemical indicators of quality. Black teacan be assessed by the eye (look), tongue(taste) and nose (smell). These factors can

be due to different quality parameters. Theblack teas produced in most Africancountries are termed as "plain" i.e. lacking

in aroma. These teas are normally pricedfor their taste and colour parameters,factors which are due to theaflavin,thearubigin and caffeine levels9. However,aroma can be an important Kenyan teaquality parameter10. Kenyan teas werenoted to have very high theaflavin levels11

compared to Central African tea (234889)and the early quest for the chemical basisto Kenyan black tea quality was mainlycentred on the study of these. Work in

Malawi12 had shown that for Central

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African black teas, there existed arelationship between the theaflavin levelsand quality as measured by sensory

evaluation and/or prices. Several studieswere therefore conducted to evaluate the

possibility of relating Kenyan tea quality totheaflavin content13. These studiesrevealed that although the linearrelationship between theaflavin levels andsensory evaluations and/or price of teawere positive, the regression coefficientwas not significant (234889). Theaflavincontent was therefore concluded to beimportant14 for Kenyan black tea quality,

but it was not the sole objective qualityindicator15. It was recognised that therewere problems with the theaflavin analysisas the results were not inter-laboratoryreproducible. The methods of theaflavinanalysis were therefore examined16.Factors causing the non-reproducibilitywere investigated and were found to berelated to infusion temperatures, altitudeat which infusion was done, size and shapeof the infusion vessel, and pH of the

infusing water17

. The methods of assayingtheaflavin were also assessed, andaluminium chloride was developed as acheap replacement to the Flavognostreagent method18. In the course of timemore methods of theaflavin analysis have

been developed. The more relevantmethod was developed in Central Africausing the C18 Cartridge Sep-Packmethod. The method was compared withthe Flavognost and aluminium chloride

methods. Although the method wasclaimed to be faster and cheaper, it wasfound to be inaccurate19. Thus the Sep-Pack method cannot be used withoutfurther modifications.

Four individual major theaflavins occurin black tea with varying contributions toastringency and/or quality. The individualtheaflavins levels vary in different black teain unpredictable manner. The lack ofsignificant relationships between Kenyan

black tea theaflavin levels and sensory

evaluation could therefore be due to this.With the advent of the HPLC analytical

procedures, it has been possible to

partition the individual theaflavins and tocalculate a normalising factor (theaflavindigallate equivalent) of the various blackteas20. A better relationship was developed

between digallated theaflavins ortheaflavins digallate equivalent andsensory evaluations21. Thus the lack ofsignificant correlation between totaltheaflavin content and sensory evaluationwas in part due to the measurement of thewrong parameter.

Volatile flavour compounds

Much research has also been done ondetermining other reliable chemical quality

parameters of tea. Flavour was known tobe an important quality parameter for tea22

but there was no quantitative method ofmeasuring it. Owuor developed a FlavourIndex by analysing the smell characteristicsof all the known aroma compounds andseparating them into two groups: those

imparting a green, grassy, undesirablesmell (Group I) and those imparting asweet flowery aroma to black tea (GroupII). A Flavour Index was then calculatedas a ratio of volatile flavour compounds inGroup I and Group II23. The FlavourIndex ratio was found to have a significantrelationship with sensory evaluation forsome Kenyan black teas24. However, theindex needs further evaluation as smellintensity of the various compounds are not

linearly related to concentration.Further work has been done to relate

lipoxygenase activity to the Group Ivolatile flavour compounds25. Theseexperiments have not yielded veryconclusive results.

Plant pigments

Further experimentation has been donewith an aim of developing a qualityselection criteria from single bushes. These

efforts were directed towards determining

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pigments which could be used to predictquality26. In these studies a negativerelationship was observed between

chlorophyll and some carotenoid levels ingreen leaf and quality (the sensoryevaluation) of black tea. The modelhowever still needs further development.

Catechins

Green tea leaves contain high levels ofpolyphenols, mainly catechins. Studieshave been reported indicating that catechinlevels could be related to black teaquality27. But these studies were hampered

by the inability to purify the individualcatechins. Recently, the work wasrestarted, but was aimed at relating thetotal polyphenols and polyphenol oxidaseactivity to quality28. A reasonablerelationship was demonstrated betweentotal polyphenols in green leaf andtheaflavin of resultant black tea. However,it was necessary to quantify the individualcatechins and relate this to theaflavin.These studies demonstrated that

polyphenol oxidase activity is not alimiting factor in Kenyan clones studiedfor the formation of theaflavin.

Experiments to develop reproduciblemethods of analysis of tannins started in1954 (17723). This early workconcentrated mainly on the effect ofinfusion time and fermentation time onnon-tanning fraction i.e. that not

precipitated by gelatine (17723). Furthercalorimetric analysis methods were

explored29

. It was also observed that thepercentage of soluble dry matter in teadecreased with fermentation duration(17722).

The main precursor to black tea qualityparameters was the level of catechins.Studies on the methods of catechinanalysis were therefore initiated30. Thesemethods were based on Thin LayerChromatography and were slow andtedious31. However, the study

demonstrated the variability of catechin

levels in the various clonal tea plants.Further studies on catechins (15549) andenzymes (15551) were done later, but the

results were inconclusive.

Caffeine

Caffeine is known to give tea itsstimulatory effects. Factors causingcaffeine variations in black tea have been asubject of several studies in Kenya32.These studies have shown that caffeinelevels in black teas vary with agronomic

practices33 and manufacturing practices34.The black tea caffeine also varied with

time of the year35

.

Aluminium and tea quality

Although aluminium has beenimplicated in Alzheimer's disease, it isknown that black tea contains largeamounts of the element. However theaddition of aluminium to tea gives the teaa good colour that is perceived to improveits 'quality'36. Factors causing variations ofaluminium contents in black tea have been

quantified37. These studies showed thatdifferent clones have varying ability toextract aluminium from the soil38 and thatincreasing rates of nitrogen reduced blacktea aluminium levels39. Aluminium alsoincreased with coarse plucking standards40

and the amount infused changed withmaceration method and grades (18988).More aluminium is infused from small

particle size black teas. Up to 40% ofaluminium in the black tea is infused into a

tea brew and this is diluted by over 200%.Thus black tea is not a serious source ofaluminium for humans. Adding aluminiumto black tea to enhance colour was shownto reduce the total theaflavin content41

although the detection of theaflavins couldbe increased by decreasing the pH of theinfusion (01760). This is likely to be dueto aluminium ions forming salts orcomplexes with the theaflavin which arenot soluble in the iso-methylbutyl ketone

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used to extract theaflavin from teainfusion.

FluoridesTea has been thought to have high

levels of fluoride (241375) which couldpredispose drinkers to fluorosis. However,the dilution factor in tea drinking is toohigh for fluoride contamination. Indeedthere is more fluoride in commonvegetables42 than in tea infusions.

Amino acids and flavour

Amino acids were speculated tocontribute to the aroma of black tea43.

Experimental basis of these were notgiven.

Quality and preharvestconditions

Agronomic and cultural practiceseffects

Quality of black tea can be dependenton many factors. These factors includeagronomic and cultural practices44. Someof the agronomic practices affectingquality are discussed below.

Agronomic practices were thought tohave influence on black tea quality.Experiments to establish this suggested

that a coarse plucking standard wasundesirable45.

Seasons

Although production of tea iscontinuous throughout the year in Kenya,it varies from month to month46. This isdue to variations in the weather factorscausing changes in growth patterns and

plant nutrient uptake47. In several studies,it has been documented that there are also

quality variations in black tea with the timeof year in Kenya48 both in the East49 andWest50 of the Rift Valley. Seasonalvariations in all quality parametersmeasured were found to follow rainfall

pattern. However, compared to aromaparameters, minimal variations wereobserved in the plain black tea quality

parameters51. Thus the seasonal changes inKenyan black tea quality were more due toaroma52 (233705; 233935) and the decline

in plain black tea quality during peakperiods is more attributable to otherfactors like inadequate factory capacitiesand unfavourable green leaf transportconditions leading to improper processingtechniques53.

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Effects of geographical area ofproduction

Black teas produced from different

parts of the world were shown to vary inquality54. Further studies have been doneto determine if the same clones grown indifferent regions have the same quality.These studies have demonstrated qualityvariations. Although the agronomicrecommended practices for tea productionin Kenya are similar55 (245778), differentfactories produce black teas with different

prices even when they have the samemanagement standards. An assessment

was done to evaluate if these processesreflected in tea sales were due to changingchemical composition and hence quality.The study was done using black teas fromvarious smallholder (KTDA) factories56.Generally black teas for the East of theRift Valley had higher TF and brightness(01777) and Flavour Index57 than black teafrom the West of the Rift Valley. Suchvariations existed even when thecomparison was done using tea materials

from the same farms sampled manytimes58. Variations could have been due tothe use of materials of different geneticmake-up. Experiments using the sameclones were therefore done59. Thesestudies did not show any quality patternswith area of production. Anotherexperiment was done within a radius ofonly 10 km but at varying altitudes tomonitor the effect of altitude on black teaquality where environmental changes were

minimal. This experiment recorded thatboth plain and aromatic black tea qualityimproved with an increase in altitude(06761; 18998; 200978; 234069). Thushigh-grown teas make black teas ofsuperior quality which explains thegenerally high quality of Kenyan teas asthey are grown at high altitudes of over1500 m above mean sea level.

The altitude at which tea is processedcaused changes in black tea quality.

Manufacture at a high altitude improved

quality of resultant black tea60. Furtherexperimentation is needed to correctlyassess and confirm this observation. There

were changes in black tea quality due todiurnal changes in plucking times also61.Factors causing these diurnal black teachanges need to be properly investigatedand quantified.

Shade trees

Tea was found originally growingunder shade trees. As a simulation of thenatural growing environment, tea-growingwas done under shade in Kenya. However,

due to reduced nutrient uptake (237597),and yields62 and an increase in diseasesusceptibility63 shade was removed in mostof Kenya's tea plantations. The effects ofshade on tea quality were investigated. Animprovement in black tea 'quality' wasobserved by sensory evaluation64. This wasconfirmed through chemical analysis inKericho65 especially on the aroma of blacktea. However, the plain black tea qualitydid not change much due to shading. This

trial needs to be done again using clonalmaterial of uniform genetic make-up toestablish the apparent lack of plain teaquality parameter changes.

Pruning

Pruning is an essentialagronomic/cultural operation in thecommercial production of tea beveragesfrom the tea plant (Camellia sinensis) (l).In Kenya, pruning is done after three to

four years as the plant reachesunmanageable heights, making pluckingcumbersome66 (200039). The plants growat faster rates after pruning which couldcause black tea quality changes. Theseeffects were evaluated67 and showed thatthe quality of black tea improved as the teaapproached the next pruning stage. In thecase of lung-pruning, the lungs produced amore superior quality of black tea thantipping leaf68. Thus it is possible to

produce black tea of varying quality

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200 Tea Quality

without changing manufacturingtechniques as long as the leaves used weregrowing at different rates.Planting

materials (clones, cultivars, varieties)Black teas produced in different parts

of the world have been shown to differ inquality69. Although the variations could in

part be due to geographical andenvironmental conditions, they could also

partly be due to the genetic make-up ofthe planting materials. Consequently it is arequirement that before planting materialis released to farmers, that the quality isassessed by sensory and chemical

methods. Several such evaluations havebeen done70. It has been shown thatdifferent clones71 and different varieties oftea72 produce black tea of different quality.The quality of the clones varies withgeography73. It is therefore critical that for

production of high quality black teas,growers are provided with materials of

proven quality in the area of intendedgrowth. So far the research has not beenvery comprehensive and more work needs

to be done to establish suitable clones fordifferent tea growing regions in Kenya.

Some studies have been carried out todetermine reliable methods of selectingclones for quality. Such methods haveincluded polyphenol contents and enzymeactivity74 , leaf pubescence (15948), leafcolour (15953), theaflavin levels75, FlavourIndex (247284; 234425), theaflavindigallate equivalent76 and plant pigments77.Although some attempts have been made

to use these parameters in clonalselection78, no single parameter has beensuccessful, which is not surprising as blacktea quality is attributed to numerous

parameters in clonal selection79.Both the Camellia sinensis var.

sinensis (China tea) and Camellia sinensisvar. assamica (Assam tea) were widelygrown in Kenya during the 1960s.However, the Assam tea has broad, softand heavy shoots which are easy to pluck

compared to the small, hard and difficult-

to-pluck leaves of China tea. Assam teahas become the most popular80. Thischange was accompanied by

improvements in black tea quality81

.Owuor and Odhiambo82 evaluated theresponse in the two different varieties.Chemical composition differences in thetwo varieties were observed whichsuggested that Assam tea had betteroverall "quality" than China tea. Owuorand Njuguna83 also compared the chemicalcomposition and quality of var. sinensisand var. assamica subsp. lasiocalyx.Again black tea quality variations were

exhibited; var. assamica had a higherFlavour Index compared to the other twovarieties. Tasters preferred var. assamicafollowed by var. assamica spp. lasiocalyx,with var. sinensis being liked the least84.The replacing of var. sinensis with var.assamica on the aforementioned physical

parameters was fortuitous, as it improvedblack tea quality in Kenya.

The age of the tea bushes (18993) andgrafting on rootstocks does not change the

quality of the scions85

.

Plucking and quality

Plucking is an expensive and importantundertaking in tea production. Incorrect

plucking reduces both quality and yieldsoccasioning uneconomic production oftea. Several studies have thereforeevaluated methods to improve both yieldsand quality through plucking.

These studies have shown that quality

of black tea improves with fine pluckingstandard86. The recommended pluckingstandard in Kenya is "two leaves and a

bud"87, although some producers areknown to advocate a coarser pluckingstandard. However there are clonalvariations in response to plucking standardwith some clones like S15/10 suited tocoarser plucking without much decline inquality88. The rate of fermentation varieswith plucking standard89. Thus for quality

tea manufacture optimal fermentation

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Tea Quality 201

duration should be changed to suit aplucking standard.

The intervals of plucking also affects

the black tea quality. If plucking standardis predetermined at two leaves and a bud,there are no drastic quality changes withlong plucking intervals. In such a situationif a shoot is more than two leaves and a

bud, only the two leaves and a bud areharvested for manufacture and the rest isleft on the plucking table. However, inorder to maintain the plucking table theextra leaves are cut back (broken back)which represents a loss of yield to the

farmers. A plucking regime should be suchthat plucking intervals take place when themaximum number of leaves are at thecorrect stage for plucking. Results fromthe Tea Research Foundation of Kenyahave shown that plucking at short

plucking intervals of 6 to 7 days leads tohigh quality black teas90, withoutsacrificing yield91. Decline in black teaquality with longer plucking intervals wasdue to the increase of coarse leaves

irrespective of nitrogen rate92

. Var.sinensis was found to be less sensitive tochanges in plucking intervals compared tovar. assamica93.

The mode of plucking also affectsquality. Due to a labour shortage,mechanical harvesters are sometimes used.A study was initiated to monitor theeffects of using shear-plucking on blacktea quality. Shears caused qualityreduction94. Motorised, machine-plucking

has also been evaluated. Compared tohand-plucking, black tea from motorised-machine-plucking was of lower quality95.Quality decline with mechanical harvesterswas made worse by longer pluckingintervals. However, the quality could beimproved by raising the harvesting blade

by 2 cm compared to 1 cm above theprevious plucking table96.

It was also recognised that good blacktea could only be obtained if the green leaf

was properly handled post- harvesting97

.

Proper leaf handling without bruising wastherefore recommended.

Fertilisers and qualityApplication of fertilisers can affect the

quality of black tea. Nitrogen has beenfound to have the largest effect on yieldand this is reflected in the number ofstudies to assess its effect on tea quality.

Studies of the effects of fertilisers wereinitiated in 198698. The quality of a highyielding clone S15/10 after application of

NPKS 25:5:5:5 and NPK 20:10:10applied at 0, 100, 300, 450 and 600 kg

N/ha/year were assessed. High rates ofnitrogen reduced the clone S15/10 bycausing decline in theaflavin levels,thearubigin levels and Flavour Index but atthe same time increasing the caffeine,Group I volatile compounds (VFC) andGroup II VFC99. The aroma qualitydeclined with an increase in nitrogen ratewas attributed to an increase in the levelsof the unsaturated fatty acids100 which

break down to produce most of the Group

I VFC101

.When the experiment on high yielding

clone S15/10 was initiated to compare theyield and quality response to nitrogen as

NPKS 25:5:5:5 or NPK 20:10:10.Symptoms of nitrogen deficiency wereobserved at low rates of nitrogen whichled to a further experiment to monitor asplit application. Fertiliser was applied asone single dose, half rates at six monthintervals, or three applications at four

month intervals. For the different sourcesof nitrogen there were seasonalfluctuations in tea quality but nitrogencontinued to depress quality overcontrol102. Indeed, splitting the nitrogenfertiliser application had no effect on teaquality but an increase in rates depressedquality103. The effects of the treatmentswere measured on the levels of aluminiumin brewed tea and there was lessaluminium after splitting the nitrogen

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202 Tea Quality

application and/or increasing the rates ofnitrogen104.

On low yielding seedling tea, there

were no effects of NPKS 25:5:5:5fertiliser at 50, 100, 200, 400 and 800 kg

N/ha/year or splitting the application intosingle, or split using half rates at 6 monthintervals or split into 4 applied after everythree months, neither the rates nor thefrequency of application had a significanteffect on black tea quality105. In the lateryears, there was a decline in tea qualitydue to nitrogen rate but splittingapplication had no effect106.

Further experiments were done on alow-yielding clone 11/4 tea in the Mt.Kenya area to determine the effects of

NPKS 25:5:5:5 rates (0, 100, 200, 400and 800 kg N/ha/year) either as a singledose or split into two equal doses at 6months intervals, on quality of black tea.High rates of nitrogen reduced quality butsplitting the application improved thequality of tea107. These experimentsdemonstrated quality benefits from

splitting fertiliser application in the EasternKenya highlands but not in WesternKenya. The decline in black tea qualitywith nitrogen persisted in all clones but atdifferent rates108 and was not affected by

planting density109.Another study of fertiliser application

monitored the effects of shade andnitrogen as NPKS 25:5:5:5 at 0, 90, 180and 270 kg N/ha/year on the quality ofseedling tea. Shade effects are summarised

elsewhere, but nitrogen rate reduced theresultant black tea quality110.The effects of nitrogen rate and

plucking intervals were measured in anexperiment111 but there were no significantdifferences due to the treatments. Theeffects of plucking intervals and nitrogenwere evaluated in another experimentwhere plucking was done at 6 or 22 dayintervals while nitrogen was applied as

NPKS 25:5:5:5 at 0, 100, 200 and 400 kg

N/ha/year. Low rates of nitrogen and short

plucking intervals improved black teaquality112. A follow-up experiment onnitrogen and frequency of harvesting was

done using the high-yielding clone S15/10.Nitrogen was applied as NPKS 25:5:5:5 at100, 200, 300, 400 and 600 kg N/ha/yearand harvesting done at 7, 14 and 21 daysintervals. Again short plucking intervalsand low rates of nitrogen produced higherquality black teas113. Short pluckingintervals therefore improves black teaquality.

The effects of rates and ratios ofnitrogen and potassium on black tea

quality were also assessed114

for tea grownin the Nyambeni Hills. Whereas increasingnitrogen rates reduced quality, rates of

potassium had no effects on the quality ofblack tea115.

The effects of organic fertilisers(compost manure from tea waste) andinorganic fertiliser NPKS 25:5:5:5) werecompared at 200 kg N/ha/year on thequality of tea. Quality differences wereobserved116.

Processing and black tea quality

Withering

There were early speculations thatthere were no benefits from withering, butit was found that the unwithered leaveswere difficult to roll and ferment due tothe excessive moisture117. Elementarynotes on tea manufacture were published

by Child118

detailing tunnel withering,chemical wither and tough withering119.The degree of wither was given as the

percentage of the weight of the originalleaf120.

Processing of black tea startsimmediately after the leaf is plucked, assoon as the leaf is detached from the plant,some chemical and biochemical changesand senescence starts121. Some of thesechanges cause variations in tea quality and

are referred to as chemical wither. The

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Tea Quality 203

changes in biochemical constituents ofgreen leaf and black tea due to witheringwere recently reviewed122. However, there

are also moisture losses making the leafflaccid and easy to macerate. Thesechanges are called physical wither. Prior to1984, it was thought that withering wasnecessary only for the benefits ofmaceration123. Consequently early studiesand literature were mainly concerned withmethods of achieving physical wither124.As a result of the fast growth of Kenya'stea production, manufacturing facilities

became a limiting factor because the green

leaf production increased faster thanfactory capacity125. Withering was thestage most adversely affected as it takesthe most space, labour and energy in thefactory (234654; 233604). Althoughwithering had also been known to affect

black tea aroma126, it was assumed theKenyan tea which previously had beenthought to be plain would not requirechemical wither. Early research thereforeassessed if Kenyan tea industry could be

affected by both physical and chemicalwither and both were found to be

positive127. Subsequent studies weregeared towards methods of efficientwithering without quality losses in theshortest duration using minimum factoryspace and energy. These studiesdemonstrated that it is possible to dochemical and physical wither at distinctstages 128. In that event it is important toachieve chemical wither before physical

wither.Methods to process black teas usingtwo separate withering stages (two-stagewither) were successfully developed andshown not to impair black tea quality129.Use of high temperature to achieve

physical wither impaired quality of theresultant black tea130. The degree of

physical wither caused changes in thequality of plain black tea. High quality

plain black teas with high theaflavin and

thearubigin content could be processed by

soft physical withers131, while aromaticblack teas benefited from both hardphysical and chemical withers132. There

was no interaction between degree ofphysical wither and fermentationduration133.

The duration of wither was found tohave an immense impact on the quality oftea. Very short withering produced good

plain black teas but with low aroma qualitywhile a very long chemical wither reducedthe quality134. Good tea quality could beobtained by withering for up to 20 hours.However it became necessary to determine

the shortest chemical wither time as thiscould reduce the time leaf has to spendwithering. These experimentsdemonstrated that chemical wither could

be achieved in as short as 6-7-hours135.These methods of withering were

determined to help reduce factoryoverheads136 without impairing quality137.For the processing of plain black teas theuse of chemical wither alone was adequatefor production of quality black teas138.

Very soft withers led to a reduced densityof black teas and increased shippingcosts139. Soft withers also led to case-hardening during firing140.

Excessive build-up of heat duringwithering (or post- plucking) also causedquality decline141. Black teas processedusing soft or chemical withers did notundergo adverse chemical changes duringstorage compared to hard-withered blackteas142.

For quality, investigations suggest thatbetter quality tea was made from pale-leafed plants than from dark-leafed plantsand that an increase in pubescence leadinto small improvement in the liquoring

properties of tea143.

Maceration

The withering process ends withmaceration. In this process the leaf isdisintegrated into small pieces by cutting

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204 Tea Quality

and/or rolling operations. The principalmachines used in the tea industry are:-

(a) The rolling machine, which

is also referred to as theorthodox process.

(b) Contra-rotating pairs ofserrated rollers, called CTC(Crush, Tear and Curl)machines.

(c) Rotating hammer-milldisintegrator, called LTP(Laurie Tea Processor)machine.

Early tea-processing in Kenya used theorthodox manufacturing method.However, this has changed with time andat present over 99% of Kenyan tea is

processed by unorthodox (CTC or LTP)systems. The change has partly been dueto the changing market patterns and theobservation that by use of unorthodoxsystems, less tea could produce more cupsof tea liquor. The effect of the change on

black tea quality was however not studieduntil recently, when a comparison wasdone between the chemical compositionafter maceration by orthodox rollers andCTC machines144. These studies revealedthat black teas produced by CTC hadhigher plain tea quality parameters i.e.theaflavin and thearubigin content,

brightness and colour, while orthodoxmanufacture lead to the production ofmore aromatic black teas. Such qualityvariations were independent of the varietyof tea used in the manufacturing

process145. Other studies compared thechemical composition and/or black teaquality variations due to the use of LTPand CTC machines. These studies revealedthat chemical composition did not differ

provided that the degree of physical witherwas maintained146. But LTP macerationneed a softer wither (higher moisture),than CTC black teas. Thus differencesobtained in the quality of these twomethods were more attributable tochanges in the degree of physical wither.

Most of Kenya's tea is processed by therotorvane followed by three CTC in series.The extent of cell wall destruction (which

allows faster and more thoroughfermentation) varies with the number ofCTC machines used. The effect ofstaggering the CTC and fermentation

processes was studied. Changing themaceration-fermentation sequence wasfound to affect black tea quality asmaceration increases the exposure ofcatechins to polyphenol oxidase. The plain

black tea quality parameters wereenhanced by having few cuts at the

beginning and having subsequent cut(s) inthe middle of fermentation147. It has notyet been shown how the differentmaceration techniques affect the individualtheaflavin composition.

Fermentation

Although many biochemicaltransformations occur during the withering

phase of tea manufacture, the mostnoticeable changes occur during

fermentation. Fermentation, whichinvolves the oxidation of catechins totheaflavins and thearubigins in the

presence of polyphenol oxidase, andunsaturated fatty acids and amino acids tovolatile flavour compounds, is thought to

be the most critical stage in teamanufacture. Quality of brewed teadepended on the process and earlyexperiments in tea manufacture centred onfermentation148.

The importance of copper in thepolyphenol oxidase enzyme activities wasrecognised and this prompted early studieson copper content of tea leaves149. It wasrecognised that low of copper contentcould reduce the fermentability of tea150.However, no relationship was established

between copper levels in green leaf andthe different oxidation ability of thedifferent tea plants. Further tests oncopper and fermentation were done by

setting up field trials with copper and

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Tea Quality 205

assessing fermentability of resultant teaand retention of copper in the soil (17720;17719; 17718).

Attempts were made to developcalorimetric methods of optimally andreliably assessing fermentation151. Theresults were promising but due to lack oftechnological development werediscontinued. The experiments onfermentation during black tea processingwere reintroduced in 1983. Theseexperiments were based on themeasurement of theaflavin content withfermentation time and showed that the in-

line TF analysis was not as accurate assensory evaluation in predicting optimumfermentation time152. Use of theaflavinlevels in brewed tea to assess fermentationtime gave closer results to sensoryevaluation. However, these methods were

post-fermentation and were of little use.This led to a search for other chemical

parameters to assess optimal fermentationduration.

The extent of fermentation can be

measured by the level of formation of theblack tea quality parameters or the amountof precursor compound black tea left inthe dhool or dried (fired) black tea. Insubsequent studies, all black tea quality

parameters and individual volatile flavourcompounds were shown to vary withfermentation duration153. The aroma of

black tea was found to decline withfermentation time154. The changes in all the

black tea quality parameters explained why

one parameter alone could not correctlyassess the optimal fermentation timeduring processing.

Fermentation is also affected by otherfactors such as the degree of physicalwither155. In a study to determine the effectof wither on fermentation time, it wasestablished that with hard physical wither,there was general decline in the formed

plain black tea quality parameters, butthere was no interaction between the

degree of physical wither and fermentation

duration156 or between fermentationduration and duration of chemical withertime157. Conditions which favoured

exposure to more oxygen or to easycontrol of temperatures favoured a morethorough fermentation158. This led into anexamination of the effects of temperatureon fermentation duration. Theinvestigations showed that fermentation athigh temperatures reduced black teaquality159. The fermentation duration didnot affect the storage of black tea after

processing160.Agronomic practices like plucking

standard and genetic make-up of thematerial also affect the fermentation.Coarsely-plucked leaf fermented fasterthan finely-plucked leaf, but produced

black tea of inferior quality161. Differentclones ferment at different rates162. Studieswere conducted to improve thefermentability of poor-fermenting clonesusing good fermenting ones. The resultsdemonstrated that a poor fermenting clone

brought down the good fermenter and vice

versa163

. The fermentability of tea can alsobe changed by varying the sequence ofmaceration with respect to fermentation.The results from all the manufacturingresearch in Kenya from 1982-1992 werereviewed164.

Wemyss (243834; 234372) hasdeveloped on commercial methods ofoptimising fermenting conditions. Thesemethods are based on use of continuousfermenters and electronically controlled

temperature, airflow and humidityregulators.Green leaf from different districts

fermented at different rates165. Causes ofthe different fermentation rates were notestablished. Early observations noted theneed to optimise fermentation time during

black tea processing and a "fermentationindex" developed which was shown to beconsistent and based on calorimetricmethods166. These results were not

adopted.

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206 Tea Quality

Drying, sorting and grading

Fermentation ends with firing (drying).Drying terminates the enzyme activity and

reduces the moisture content to a state inwhich the black tea can be stored. Duringthe process many of the volatile flavourcompounds are lost167. Fortunately ahigher proportion of Group I VFC whichare responsible for an undesirable aromato black tea is lost compared to the morearomatic Group II.

Drying was done using a conventionaldrier in which drying "dhool" is put on amoving bed. However, in recent years,

many fluid bed dryers have beendeveloped. When operated under optimalconditions, there were no detectable plaintea quality changes due to the type of drierused, but the aroma and bulk density wereimproved by use of fluid bed dryer168.

Dryer temperature settings are difficultto control in different dryers and theeffects of different fluid bed driers have

been the subject of study. Black tea qualitycan therefore vary due to variations in the

temperature settings and air movement169.Even with optimal dryer settings thedegree of physical wither can affect thedryer performance and resultant black teaquality170. Very soft physical withersreduce drier throughput and can result inthe break-down of a fluid bed dryer. Useof solar heating can also reduce cost ofdrying tea in Kenya (243740), but thisoption has not been thoroughlyinvestigated.

The dried black teas are finally storedto remove fibre and then graded. Smaller

particle grade black teas make better plainteas than large particle grades while thearomatic characteristics are better with alarger particle grades171. The quality of the

black teas is routinely assessed by sensoryevaluation or/and chemical analysis172.

Effects of storage have also beenassessed on quality173 and quality wasnoted to deteriorate upon storage.

Recently storage was re-investigated with

respect to packing material174 and methodof packaging175. For the packagingmaterial, preliminary data showed that a

tea chest lined with either a paper sack ora manilla bag were effective in storing

black tea176. Packing under vacuum ornitrogen seemed to show some promise177

but the data need to be properly evaluated.Further tea-processing machinery is

being developed by the Sotik Tea Co. Ltd.(234372).

Taints in black tea

Black tea can easily be contaminated

by taints if some agronomic andprocessing procedures are not donecorrectly. Treating the tea with 2,4-Dresulted in brewed black tea with taints178.Direction of use of pesticides on tea wastherefore given to avoid contaminationand taints (244540).

It had been speculated that aerialapplications of urea lead to tainting of tea

but this did not seems to be the case179.Taints were later shown to be caused by

contamination by airflow from rotting fuelwood180. Proper airflow into the factory isvital and if it is not correctly done, cancause fungicidal taint contaminations(242506).

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Tea Quality 207

Purity

For quality, the investigations suggestthat better quality tea was made from pale-

leafed plants than from dark-leafed plantsand that an increase in pubescence leadinto small improvement in the liquoring

properties of tea181.

Storage of processed tea

Child discussed moisture absorptionand oven methods of determining moisturecontent of made tea in 1958182. It wasrecognised that tea undergoesdeterioration upon storage, and a study

was done on East African tea to monitorchemical changes due to storage postmanufacture183. Although the studyobserved variations in the theaflavinslevels, other black tea quality parameterswere not studied.

The purity of tea was discussed byTolhurst184. This discussion was not basedon experimentation.

The role of miniature manufacturing

unitsThe use of miniature manufacturing

units in experiments were initiated in 1974to assess the effect of different agricultural

practices on processed tea quality185.These experiments continued insubsequent years186. However, the resultsof the analysis were not given. After theinitiation of the TRFK, many miniaturemanufacturing experiments have beenconducted for plant improvement187. The

results from plant improvement studieshave been extensively used to form the

basis of clonal selection for quality. Thusclones released from 1982 onwards wereevaluated for quality using the miniaturemanufacture. The miniature manufacturingunit has been under continuousimprovement to ensure reproducibility andreliability of generated data188.

Thorough studies on the manufactureof black tea were initiated in 1982. Several

miniature manufacturing experiments were

done to evaluate the possible existencebetween theaflavin levels and sensoryevaluation as had been exhibited in Central

Africa. Correlation of theaflavin levels andtasters' evaluations were however lesssignificant189. The results from thetheaflavin and sensory evaluation workhave been used to establish the basis ofKenyan tea quality (see under chemical

basis of quality).

Factory organisation

Principles of factory organisationwere presented by Eden to the SecondTea Research Institute of East Africaconference held in 1954190. Stansell191

discussed the layout of factory asexemplified by Tagabi. The discussionwas based on experience not researchresults.

References

8/22/2019 Vol 26 13 Quality

14/32

1 Eden T. 1950. The chemistry of tea manufacture Tea Research Institute East Africa Annual Report 1950, pp 12-13.

2Eden T. 1954. Tea research problems in East Africa. Tropical Agriculture31, 112-118.

3Eden T. 1954. Morphological basis of quality in tea.Nature, 124, 844.

413414; Eden T. 1950. The chemistry of tea manufacture Tea Research Institute East Africa Annual Report 1950, pp

12-13.

514884, Child R. 1953. The chemistry of tea.Tea Research Institute East Africa Annual Report, pp 33-36.

6Child R. 1954. The chemistry of the tea leaf in relation to manufacture. Tea Research Institute East Africa Pamphlet

no 8, pp 9-16.

7Hainsworth E. 1969. Tea in "Encyclopedia Chemical Technology Vol 19 pp 743-755.

8Child R. 1959. The tea taster and the chemist Tea Research Institute East Africa Pamphlet no 17, pp 37-48.

9Owuor PO. 1995. Improvement of black tea quality - Kenyan experience. Proceedings of Regional Tea Research

Seminar, Blantyre, Malawi:21-23rd March.

10 233705; 234425; Robinson JM, Owuor PO. 1992. Tea aroma. In "Tea Cultivation to consumption, (Wilson KC. and

Clifford MN. Eds). Chapman and Hall, London, 1st edition, chapter 18, pp 603-642.

11234889; 234745; 243950; Owuor PO. 1983. Black tea standards. Study based on teas from different factories. Tea

Research Foundation of Kenya Annual Report 1983, pp 30-33; Owuor PO, Othieno CO, Reeves SG. 1986. Theeconomic impact of theaflavins in Kenyan teas. Tea, 7, 88-93.

12Owuor PO. 1982. Can theaflavins alone be adequate parameters in tea quality estimation: A review. Tea, 3(2), 36-40.

13Owuor PO. 1982. Theaflavins content as an index for processing black tea from Kenya. Tea Research Foundation of

Kenya Annual Report 1982, pp 12-15; Owuor PO. 1983. Miniature manufacture for correlation of theaflavins contentsand tasters evaluation. Tea Research Foundation of Kenya Annual Report 1983 pp 20-23; Owuor PO. 1983.Correlation of theaflavins contents of made tea from different factories and tasters evaluation. Tea Research Foundation

of Kenya Annual Report 1983 pp 24, 27-29; Owuor PO. 1983. Theaflavins as a basis for pricing Kenya black Tea411-16; Owuor PO. 1983. Black tea standards. Study based on teas from different factories. Tea Research Foundationof Kenya Annual Report 1983, pp 30-33; Owuor PO. 1983. Prices of Kenya teas and tasters' evaluation. Tea,4(1), 16-20; Owuor PO, Njuguna CK. 1982. Miniature manufacture. Tea Research Foundation of Kenya Annual Report 1982

pp 9-12; Owuor PO, Wanyoko JK. 1982. Miniature manufacture and tea liquor quality. Tea, 3(2), 4-5; Othieno CO,Owuor PO. 1984. Black tea quality and International standards. International Tea Journal 7, 27-30; Owuor PO,Reeves SG. 1984. Miniature manufacture for correlation of theaflavins contents with tasters evaluation. Tea Research

Foundation of Kenya Annual Report 1984, pp 65-66; Owuor PO, Reeves SG, Obanda AM. 1985. Miniaturemanufacture for correlation of theaflavins content with testers evaluation. Tea Research Foundation of Kenya Annual

Report 1985, pp 60-61; Owuor PO, Reeves SG, Obanda AM. 1986. Miniature manufacture for correlation oftheaflavins contents with tasters evaluation. Tea Research Foundation of Kenya Annual Report 1986, pp 88-89.

14McDowell I, Owuor PO. 1992. The taste of tea. New Scientist1803, 30-33.

15243950; 234889; 234745; Owuor PO, Othieno CO, Reeves SG. 1986. The economic impact of theaflavins in Kenyan

teas. Tea, 7, 88-93.

16Reeves SG, Owuor PO. 1984. Catechins and theaflavins. Tea Research Foundation of Kenya Annual Report 1884 . pp

70-71.

1715546; 18991; Owuor PO, Reeves SG, Obanda AM. 1985. Studies on tea standards. Tea Research Foundation of

Kenya Annual Report 1985, pp 64-71; Reeves SG, Gone FO. 1984. The effect of infusion temperature on measuredtheaflavins. A preliminary note. Tea, 5(1), 5-8; McDowell I, Reeves SG, Owuor PO, Gone FO. 1985. Between

8/22/2019 Vol 26 13 Quality

15/32

laboratory variation of the Flavognost assay for theaflavins in black tea. Tea, 6(2), 25-31.

1815546; 18991; Owuor PO, Reeves SG, Obanda AM. 1985. Studies on tea standards. Tea Research Foundation of

Kenya Annual Report 1985, pp 64-71; Reeves SG, Gone FO, Owuor PO. 1985. Theaflavins analysis of black tea:-problems and prospects. Food Chem.18, 199-210; Reeves SG, Owuor PO. 1984. Methods of theaflavins analysis. TeaResearch Foundation of Kenya Annual Report 1993, pp 71-77.

19 Owuor PO, Obanda M. 1993. Comparison of commonly used, published methods of analysis of theaflavins. TeaResearch Foundation of Kenya Annual Report 1993 pp 95-96; Owuor PO, Obanda M. 1995. Comparison ofspectrophotometric assay methods for theaflavins and thearubigins in black tea. Tea, 16, 41-47.

20Owuor PO. 1993. The impact of individual theaflavins levels on astringency of black tea. Tea Research Foundation of

Kenya Annual Report 1993 pp 96-102; Owuor PO, Orchard JE, McDowell J. 1994. Changes in the qualityparameters of clonal tea due to fermentation time. J. Sci. Food Agric 66 533-561; Owuor PO, McDowell I. 1994.Changes in theaflavins composition and astringency during black tea fermentation. Food Chem 51, 251-254; OwuorPO, Obanda M. 1994. Evaluation of clonal tea quality and impact of individual theaflavins on black tea sensoryevaluation. Tea Research Foundation of Kenya Annual Report 1994 , pp 94-96; Owuor PO. 1993. The impact ofindividual theaflavins levels on astringency of black tea. Tea Research Foundation of Kenya Annual Report 1993 pp96-102; Owuor PO, Obanda M. 1995. Clonal variations in the individual theaflavins and their impact on astringencyand sensory evaluation.Food Chemistry 54, 273-277.

21Owuor PO. 1993. The impact of individual theaflavins levels on astringency of black tea. Tea Research Foundation of

Kenya Annual Report 1993 pp 96-102; Owuor PO, Obanda M. 1995. Clonal variations in the individual theaflavinsand their impact on astringency and sensory evaluation.Food Chemistry 54, 273-277.

22Owuor PO. 1986. Flavour of black tea. A review Tea, 7, 29-42; Mndewa BSE. 1977. Plant leaf surface lipids: Age

variation patterns in Coffea arabica L. and Thea sinensis L.,M.Sc. Thesis, University of Nairobi.

23234425; 247284; Owuor PO. 1986. Some manufacturing, agronomic acid ecological effects on the chemical

composition and quality of black tea. TheMatsumae International Fellowship Report 1986, Tokyo, Japan, pp 113-112.

24234425; 247284; Owuor PO. 1986. Some manufacturing, agronomic acid ecological effects on the chemical

composition and quality of black tea. The Matsumae International Fellowship Report 1986, Tokyo, Japan, pp 113-112;Owuor PO. 1991. Establishment of reliable aroma quality parameters. Tea Research Foundation of Kenya Annual

Report 1991, pp 113-117.

25Obanda M, Owuor PO. 1992. Lipoxygenase activity. Assay procedure, effect of clone plucking standard and wither

method. Tea Research Foundation of Kenya Annual Report 1992, pp 116-119; Obanda M, Owuor PO. 1993.Changes in shoot xylem water potential, lipoxygenase activity in green tea shoots and formation of volatile in black teas

produced under chemical and normal wither conditions. Tea Research Foundation of Kenya Annual Report 1993 , pp135-142.

26Obanda M, Owuor PO. 1992. Variation of chlorophyll content in different parts of tea shoot. Tea Research

Foundation of Kenya Annual Report 1992, pp 105-110; Obanda M, Owuor PO. 1993. Variations of chlorophyll

content and other quality parameters in black teas manufactured from different clones and shoot maturity. TeaResearch Foundation of Kenya Annual Report 1993, pp 132-134; Obanda M, Owuor PO. 1994. Clonal variation oftotal Polyphenols contents in green leaf black tea quality. Tea Research Foundation of Kenya Annual Report 1994 , pp96-100; Obanda M, Owuor PO. 1995. Clonal variations in chemical quality parameters and tasters and tastersevaluation of black tea due to green leaf plucking standards. Food Chem. in press; Taylor S, Baker D, Owuor P,Orchard JE, Othieno CO, Gay C. 1992. Model for predicting black tea quality from the carotenoid and chlorophyllcomposition of fresh green leaf. J.Sci. Food Agric. 58, 185-189; Taylor S, Owuor P, Gay C. 1991. Predicting blacktea quality from plant pigment composition of the fresh green leaf using multiple regression model: Effects of season or

predictive performance.In contribution of Tea Science to Human Health: Proceedings of International symposium ontea Science, Shizuoka, Japan 26-29th Aug, pp 120-124; Taylor SJ, Owuor PO. 1990. Natural Resources Institute -Tea Research Foundation of Kenya collaborative project. Tea Research Foundation of Kenya Annual Report 1990, pp

8/22/2019 Vol 26 13 Quality

16/32

120-121; Obanda M, Owuor PO. 1994. Effect of shoot maturing and processing on the residual chlorophyll content,composition of volatile flavour compounds and plain black tea quality parameters. Proceedings of Kenya Institute of

Food Technologies Conference Serena Hotel, Nairobi, 7th-9th November.

27Reeves SG, Owuor PO. 1984. Catechins and theaflavins. Tea Research Foundation of Kenya Annual Report 1884 . pp

70-71; Reeves SG, Obanda AM, Owuor PO. 1985. Enzymology Tea Research Foundation of Kenya Annual Report1985, pp 74-78; Obanda MA, Owuor PO, Reeves SG. 1985. Catechins. Tea Research Foundation of Kenya Annual

Report 1985, pp 72-73; Obanda AM. 1990. The Oxidation of simple and complex Polyphenols by laccase.PhD Thesis,University of London; and Diploma of Imperial college; Obanda M. 1993. Laccase Oxidation of tea leaf Polyphenols.Proceedings of Inaugural Conference of Kenya Chemical Society. University of Nairobi, 7-11th June 1993, pp 81-83.

28Obanda M, Owuor PO. 1992. The impact of clonal variation of total polyphenols content and polyphenol oxidase

activity of fresh tea shoots on plain black tea quality parameters. Tea Research Foundation of Kenya Annual Report1992, pp 110-112; Obanda M, Owuor PO. 1993. The correlation of total polyphenols content in fresh tea shoots, plain

black tea quality parameters and tasters preferences of AHP clones. Tea Research Foundation of Kenya Annual Report,pp 132, 134-135; Obanda M, Owuor PO. 1993. Effect of time of the year on polyphenol oxidase activity and totalpolyphenols contents in fresh tea shoots and on plain black tea quality parameters of Sotik tea. Tea ResearchFoundation of Kenya Annual Report 1993, pp 142-144; Obanda M, Owuor PO, Njuguna CK. 1992. The effect totalpolyphenol content and polyphenol oxidase activity of fresh tea shoots on plain black tea quality parameters.Proceedings of 1st NAPRECA Seminar Day-Natural Products for Development, University of Nairobi, 20th November;Obanda M, Owuor PO, Njuguna CK. 1992. The impact of clonal variations in polyphenols content and polyphenoloxidase in fresh tea shoots on plain black tea quality parameters. Tea, 13, 129-133.

29 17721; Todd JR. 1955. Colorimetric methods for studying fermentation process in black tea manufacture. Chemistry

and Industry 704-705.

30 15549, 32221, Wanyoko JK. 1977. Analysis of catechins in fresh tea leaves. Tea in East Africa17(1). I; Wanyoko

JK. 1978. Catechins analysis in fresh tea leaves. Tea Research Institute East Africa Annual Report 1978, pp 13-14.

3132221, Wanyoko JK. 1979. Analysis of catechins in fresh leaves of East African tea. Tea in East Africa19(2). 3-5;

Wanyoko JK, Munavu RM. 1985. Simple thin layer chromatography (TLC) methods for separation of catechins fromfresh tea leaves.Kenya J. Sci. Technol6(A), 119-126.

3215554; 202379; Owuor PO. 1984. Caffeine contents of clonal teas. Tea Research Foundation of Kenya Annual Report

1984, pp 78-79..

33202379; 234258; 241676; 241665; 246037; Owuor PO. 1987. Some factors causing variation in caffeine contents of

tea. Tea, 8, 82-88; Owuor PO. 1987. Variations in the caffeine contents of tea due to some agronomic andmanufacturing practices.Proceedings of International Symposium and the Chemistry of Tropical Natural Products. 24-28th August, Moi University Eldoret; Owuor PO. 1988. Some advances in improvement of tea quality throughchemical research.Proceedings of Second symposium on Natural Products and Workshop on Development of Databases, Nairobi, 12-15th September, P 14; Owuor PO. 1993. Varietal and clonal chemical composition and qualityvariations of black tea Camellia sinensis (L.) in Kenya. Proceedings of Inaugural conference of Kenya ChemicalSociety, University of Nairobi, Kenya 7-11th June, pp 71-73; Owuor PO. 1993. Comparative studies on black teaquality and chemical composition of different varieties and clones of Camellia sinensis in Kenya: A review Tea14 54-60.

34 244004; 200529; 241665; Owuor PO. 1987. Variations in the caffeine contents of tea due to some agronomic and

manufacturing practices.Proceedings of International Symposium and the Chemistry of Tropical Natural Products. 24-28th August, Moi University Eldoret; Owuor PO. 1988. Some advances in improvement of tea quality throughchemical research.Proceedings of Second symposium on Natural Products and Workshop on Development of Databases, Nairobi, 12-15th September, P 14; Owuor PO, Othieno CO. 1988. Factors affecting tea quality. Post harvestvariable varieties. A review. Tea,9, 86-95.

35202379; 234258; Owuor PO. 1985. Caffeine contents of clonal teas. Tea Research Foundation of Kenya Annual

Report 1985 pp 79-80; Owuor PO. 1984. Caffeine contents of tea. Tea Research Foundation of Kenya Annual Report1984, pp 78-79; Owuor PO. 1987. Some factors causing caffeine variations in tea. Tea, 8, 82-88.

8/22/2019 Vol 26 13 Quality

17/32

36Reeves SG, Gone FO, Owuor PO. 1985. Theaflavins analysis of black tea- problems and prospects. Food Chem.18,

199-210.

3718358; 01783; 18988; Owuor PO, Gone FO, Onchiri DB, Jumba IO. 1990. Levels of aluminum in green leaf of

clonal teas, black tea and tea liquors and effects of rates of nitrogenous fertilizer on the levels of aluminum in black tea.Food Chemistry, 35, 59-68.

38 18988; 01783; Owuor PO, Gone FO, Onchiri DB, Jumba IO. 1990. Levels of aluminum in green leaf of clonal teas,

black tea and tea liquors and effects of rates of nitrogenous fertilizer on the levels of aluminum in black tea. FoodChemistry, 35, 59-68.

39Owuor PO. 1988. Effect of high rates on nitrogenous fertilizer on aluminum contents of black tea. Tea Research

Foundation of Kenya Annual Report 1988, pp 51-52; Owuor PO, Gone FO, Onchiri DB, Jumba IO. 1990. Levels ofaluminum in green leaf of clonal teas, black tea and tea liquors and effects of rates of nitrogenous fertilizer on the levelsof aluminum in black tea. Food Chemistry, 35, 59-68.

40Owuor PO. 1987. Aluminum in tea. Tea Research Foundation of Kenya Annual Report 1987pp 72-74.

4101759; Owuor PO, Gone FO. 1988. Effects of added aluminum on theaflavins contents of black tea. Tea 9, 81-85.

42Owuor PO. 1985. Fluoride contents of vegetables from different parts of Kenya. Food chem, 18, 283-289.

43Child R, Todd JR. 1955. The chemistry of tea fermentation. Tea Research Institute East Africa Annual Report 1955

pp 26-29.

44Owuor PO. 1995. The Improvement of Plain Black Tea Quality By Agronomic Practices: Kenyan Experience.

Proceedings of Regional Tea Research Seminar. Blantyre, Malawi. 21-23rd March, 1995.

45Child R. 1953. Distribution of material in the flush. Tea Research Institute East Africa Annual Report 1953 pp 36-38.

46Owuor PO. 1994. Clonal variations in the response of black tea (Camellia sinensis (L) quality parameters the time of

the year in the Western Kenya highlands. Tropical Science 34, 225-230; Owuor PO, Wanyoko JK, Othieno CO.1990. High rates of nitrogen on tea I.Response and distribution of yield and clonal tea. Tea11, 78-89; Odhiambo HO,Owuor PO, Othieno CO. 1988. Factors affecting tea quality. I Agronomic practices. A review. Tea, 9, 36-40; OwuorPO. 1987. Seasonal variations in tea quality. Tea Research Foundation of Kenya Annual Report 1987, pp 79.

47Owuor PO, Wanyoko JK, Othieno CO. 1990. High rates of nitrogen on tea. II. Monthly changes in mature leaf

nitrogen, phosphorous and potassium contents, Tea11 90-95; Wanyoko JK, Owuor PO, Othieno CO. 1990. Highrates of nitrogen in mature leaf calcium, manganese and aluminum contents Tea11 96-100.

48Owuor PO, Obanda M, Othieno CO. 1992. Changes in black tea quality from some smallholder factories with time

of the year. Tea Research Foundation of Kenya Annual Report 1992, pp 105-109; Owuor PO, Obanda AM. 1991.Changes in black tea quality due to time of the year from some small-holder factories Tea Research Foundation of

Kenya Annual Report 1991, pp 165, 167-170; Obanda M, Owuor PO. 1993. Effect of time of the year on polyphenoloxidize activity and total polyphenol content in fresh tea shoots on plan black tea quality parameters of black tea. TeaResearch Foundation of Kenya Annual Report 1993, pp 142-144; Owuor PO, Obanda M, Othieno CO. 1993. Qualityperformance of a few selected smallholder tea factories Tea,14 31-43; Owuor PO. 1991. Changes in tea quality, yieldsand weather factors with time of the year.In "Improving Tea Manufacture Through Research". Proceedings of Seminar

For Small-Holder Tea Factory Managers, (Othieno CO, Owuor PO, Orchard JE. eds), Tea Research Foundation ofKenya, Kericho. 15th-16th and 22nd-23rd January 1991. pp 47-51.

4901757; 19002; 233705; Owuor PO. 1988. Effects of seasons and nitrogen on yield and chemical composition of clonal

black tea. Tea Research Foundation of Kenya Annual Report 1988,pp 62, 64; Owuor PO. 1989. Variations in seedlingtea quality in relation to time of the year at Nyambeni Hills. Tea Research Foundation of Kenya Annual Report 1989.

8/22/2019 Vol 26 13 Quality

18/32

pp 82-83; Owuor PO. 1990. Changes in yield and quality parameters of seedling tea due to time of the year inNyambeni Hills. Tea Research Foundation of Kenya Annual Report 1990, 90-92.

5017265; 233935; Owuor PO. 1989. Response of clonal tea to nitrogen and time of the year. Tea Research Foundation of

Kenya Annual report 1989 pp 82, 84-85; Owuor PO. 1990. Interclonal black tea variations in the chemical qualityparameters due to time of the year at Changoi Estate. Tea Research Foundation of Kenya Annual Report 1990 , pp 92-94; Owuor PO. 1990. Response of black tea quality parameters and yields to nitrogen application and frequency of the

application. Tea Research Foundation of Kenya Annual Report 1990 , pp 94-96; Owuor PO. 1991. Response of blacktea quality parameters to rates of nitrogen, splitting nitrogen application and time of the year. Tea Research Foundationof Kenya Annual Report 1991, p 130, 133; Owuor PO. 1991. Changes in chemical composition of Kenya black teas inrelation to time of the year and weather factors. In "Contribution of Tea Science to Human Health."Proceedings of

International Symposium on Tea Science. Shizuoka, Japan 26-29th August 1991, pp 165-199; Owuor PO. 1991.Interclonal black tea variations in the chemical quality parameters due to time of the year at Changoi Estate. Tea

Research Foundation of Kenya Annual Report 1991, pp 92-93.

51233935; 233705; Owuor PO. 1991. Interclonal black tea variations in the chemical quality parameters due to time ofthe year at Changoi Estate. Tea Research Foundation of Kenya Annual Report 1991 , pp 92-93. Owuor PO. 1991.Changes in chemical composition of Kenya black teas in relation to time of the year and weather factors. In"Contribution of Tea Science to Human Health."Proceedings ofInternational Symposium on Tea Science. Shizuoka,Japan 26-29th August 1991, pp 165-199; Owuor PO. 1991. Response of black tea quality parameters and yield tonitrogen application and frequency of application. Tea Research Foundation of Kenya Annual Report 1991 , pp 94-95;Owuor PO. 1992. High rates of nitrogen on tea of high altitude. VI. Changes in clonal black tea quality due to time ofthe year rates and splitting nitrogen application. Tea13 36-43.

52Owuor PO. 1994. Clonal variations in the response of black tea (Camellia sinensis (L) quality parameters the time of

the year in the Western Kenya highlands. Tropical Science34, 225-230.

53Owuor PO. 1995. Improving the quality of black tea by agronomic practices. Proceeding of Regional Tea Seminar.

Blantyre, Malawi, 21-23rd March.

54Horita H, Owuor PO. 1987. Comparison and characterization of volatile components of Kenyan clonal black teas and

various black teas from other producing areas of the world. Bulletin of the National Institute of Vegetables, OrnamentalPlants and Tea (Japanese)1(B), 55-65; Owuor PO. 1986. Some manufacturing, agronomic and ecological effects orthe chemical composition and quality of black tea. The Matsumae International Foundation Research Report 1986,Tokyo, Japan, pp 125-166; Owuor PO. 1986. Comparison of the chemical composition of black tea from main

producing parts of the world. Tea Research Foundation of Kenya Annual Report 1986, pp 95-96; Owuor PO,Tsushida T, Horita H, Murai T. 1986. Comparison of the chemical composition of black teas from main tea

producing parts of the world. Tea, 7, 71-78.

55Othieno CO. 1988. A summary of recommendations and observations from TRFK. Tea, 9, 50-65.

56Rotich MK. 1989. Determination of the levels of the micro-elements (Al, Cu, Pb, Mo, Cd) in manufactured tea from

various Kenya Tea Development Authority factories in Kenya. B.Sc. Project, University of Nairobi.

57Owuor PO, Othieno CO. 1987. Environmental effects on tea quality I. Locational effects on chemical composition and

quality of clonal teas Proceedings of International Symposium on the chemistry of Natural Products 24-28th Aug. MoiUniversity, Eldoret, Kenya; Owuor PO, Obanda AM, Othieno CO. 1991. Changes in the chemical composition of

black teas from different factories. Tea Research Foundation of Kenya Annual Report 1991, pp 165-166.

58 239996; Muritu JW. 1989. Effects of some agronomic practices on the fatty acids content and composition of tea

leaves. MSC thesis, University of Nairobi. Owuor PO, Obanda AM. 1991. Changes in black tea quality due to time ofthe year from some small-holder factories Tea Research Foundation of Kenya Annual Report 1991 , pp 165, 167-170;Owuor PO, Obanda AM, Othieno CO. 1991. Changes in the chemical composition of black teas from differentfactories. Tea Research Foundation of Kenya Annual Report 1991, pp 165-166; Owuor PO, Othieno CO. 1991.Response of black tea quality to locality in small holder tea farms. Tea,12, 41-45.

8/22/2019 Vol 26 13 Quality

19/32

5917270; 234425; 18998; 247284; Owuor PO. 1986. Some manufacturing, agronomic and ecological effects or the

chemical composition and quality of black tea. The Metsumae International Foundation Research Report 1986, Tokyo,Japan, pp 125-166; Owuor PO, Njuguna CK. 1988. Geographical areas of production effects on the fatty acidscomposition of young shoots. Tea Research Foundation of Kenya Annual Report 1988, pp 59-62; Owuor PO, ObandaMA, Tsushida T, Horita H, Murai T. 1987. Geographical variations of theaflavins, thearubigins, caffeine in Kenyaclonal black tea. Food Chemistry, 26, 223-230; Aishima T, Togari N, Owuor PO. 1995. Chemometrics PatternRecognition and Calibration Techniques Applied to Volatile Components and Sensory Quality of Kenya Black Tea.

Food Sci. Technol. Int. 1(1), 38-43.

60Owuor PO, Obanda AM. 1991. Effect of altitude of manufacture on black tea quality. Tea Research Foundation of

Kenya Annual Report 1991, pp 135, 137.

61200004; Owuor PO, Orchard JE. 1989. The effect of temperature during withering on black tea quality parameters of

seedling tea. I.Tea Research Foundation of Kenya Annual Report 1989, pp 95-98; Owuor PO, Orchard JE. 1989. Theeffects of withering parameters of black tea quality parameters of black tea of clone S15/10. Tea Research Foundationof Kenya Annual Report 1989, pp 93-95; Othieno CO, Owuor PO, Orchard JE. 1991. Improving black teamanufacture through research. Proceedings of Seminar for Smallholder Tea Factory Managers. Tea ResearchFoundation of Kenya, Kericho. 15-16th and 22-23rd Jan, pp 1-53.

62 237597; 239985; McCulloch JSG, Pereira HC, Kerfoot O, Goodchild NA. 1965. Effect of shade trees on yields.

Agriculture and Meteorology, 2, 385-399; Othieno CO, Ngetich WK. 1992. Studies on the use of shade in teaplantation in Kenya II. Effects on yield and their components Tea, 13, 100-110; Obaga SMO, Othieno CO. 1987.Effect of different types of shade and nitrogen rates on tea yields. Tea, 8(2), 57-62.

63Eden T. 1976. "Tea" in Tropical Agriculture series. 3rd edition, Longman, England.

64 12632; McCulloch JSG, Pereira HC, Kerfoot O, Goodchild NA. 1965. Effect of shade trees on yields. Agriculture

and Meteorology,2, 385-399.

65 241076; 241676; 241665; 17264; 19879; Owuor PO, Othieno CO. 1987. The effects of shade and nitrogen fertilizer

rates on quality of seedling tea. Tea Research Foundation of Kenya Annual Report 1982 pp 59-62; Owuor PO,Othieno CO, Howard GE, Robinson JM, Cooke RD. 1987. Environmental effects on tea quality. II. The effect of

shade and nitrogenous fertilizer rates on chemical composition and quality of seedling tea. Proceedings of InternationalSymposium on the chemistry of Tropical Natural products. 24-28th Aug. Moi University, Eldoret Kenya.

66Mwakha E. 1991. Lung size and timing of pruning. Tea Research Foundation of Kenya Annual Report1990 pp 18-

19.

6719689; 234069; 241665; 241676; 201331; Muritu JW. 1989. Effects of some agronomic practices on the fatty acids

content and composition of tea leaves. Msc Thesis, University of Nairobi; Owuor PO. 1988. Changes in fatty acidslevels with time from lest prune. Tea Research Foundation of Kenya Annual Report 1988 , 107,111; Owuor PO. 1993.Impact of rim-lung pruning and nitrogenous fertilizers on clonal black tea quality. Tea Research Foundation of Kenya

Annual Report 1993. pp 108-109; Owuor PO. 1994. Effects of lung pruning and nitrogen fertilizer on black tea quality.Tea, 15, 4-7.

68Owuor PO. 1993. Impact of rim-lung pruning and nitrogenous fertilizers on clonal black tea quality. Tea Research

Foundation of Kenya Annual Report 1993. pp 108-109; Owuor PO. 1994. Effects of lung pruning and nitrogenfertilizer on black tea quality. Tea, 15, 4-7.

69Horita H, Owuor PO. 1987. Comparison and characterization of volatile components of Kenyan clonal black teas and

various black tea from other producing areas of the world. Bulletin of the National Research Institute of Vegetables,Ornamental plants and Tea (Japan) 1(B), 55-65; Owuor PO. 1986. Comparison of teas from different parts of theworld. Tea Research Foundation of Kenya Annual Report 1986, pp 95-96; Owuor PO. 1986. Some manufacturing,agronomic and ecological effects on the chemical composition and quality of black tea. The Metsumae International

Foundation Research Report 1986, Tokyo, Japan, pp 125-666; Owuor PO, Tsushida T, Horita H, Murai T. 1986.

8/22/2019 Vol 26 13 Quality

20/32

Comparison of the chemical composition of black tea from main tea producing parts of the world. Tea,7, 71-78.

7018355; 21950; Owuor PO, Njuguna CK. 1982. Miniature manufacture. Tea Research Foundation of Kenya Annual

Report 1982 pp 9-12; Owuor PO. 1983. Miniature manufacture for plant improvement. Tea Research Foundation ofKenya ANNUal Report 1983, pp 13-20; Owuor PO. 1984. Miniature manufacture for plant improvement. TeaResearch Foundation of Kenya Annual Report 1984. pp 60-64; Owuor PO. 1989. Clonal selection through quality.Tea Research Foundation of Kenya Annual Report 1989, pp 81-82; Owuor PO. 1993. Varietal and clonal chemical

composition and quality variations of black tea Camellia sinensis (L) in Kenya.Proceedings of inaugural conference ofKenya Chemical Society. University of Nairobi. 7-11th June, pp 71-73; Owuor PO. 1993. Impact of individualtheaflavins levels on astringency of black tea. Tea Research Foundation of Kenya Annual Report 1993, pp 96-102;Owuor PO, Njuguna CK. 1990. Assessment of quality clones under test. Tea Research Foundation of Kenya Annual

Report 1990, pp 89-90.

71244249; 202379; 234258; 241676; Obanda M, Owuor PO, Njuguna CK. 1992. The effect of total polyphenol contentand polyphenol oxidase activity of fresh tea shoots in pain black teas quality parameters. Proceedings of ist NAPREASeminar Day - Natural Products For Development. 20th November, University of Nairobi, Nairobi; Obanda M,Owuor PO, Njuguna CK. 1992. The impact of clonal variations in polyphenol content and polyphenol oxidase activityin fresh tea shoots on plain black tea parameters Tea, 13, 129-133; Owuor PO. 1992. Tea; The chemistry in year cup:Its quality and how that is affected by agronomic practices. The 1992 ICIPE Guest Speakers Seminar Series., 7th July.Duduvile, Nairobi, Kenya; Owuor PO. 1992. Optimising manufacture for improved quality of Kenyan black teathrough biochemical and chemical research. Proceedings of 1st NAPRECA National Seminar Day: Natural Products

for Development. 20th Nov. University of Nairobi, Kenya; Owuor PO. 1993. Varietal and clonal chemical compositionand quality variations of black tea Camellia sinensis (L) in Kenya. Proceedings of inaugural conference of KenyaChemical Society. University of Nairobi. 7-11th June, pp 71-73;; Owuor PO, Obanda M. 1994. Evaluation of tea forquality and impact of individual theaflavins on black tea sensory evaluation. Tea Research Foundation of Kenya

Annual Report 1994, pp 94-96; Owuor PO, Obanda M. 1995. Clonal variation in the individual theaflavins and theirimpact on astringency and sensory evaluationFood Chemistry (in press).

72233565; Owuor PO, Odhiambo HO. 1991. Response of black tea chemical quality parameters of two tea varieties to

methods and frequencies of harvesting Tea Research Foundation of Kenya Annual Report 1991, pp 118, 120-122;Owuor PO, Njuguna CK. 1991. Characteristics of chemical quality parameters of black tea from different varietiesand their response to method of manufacture. Tea Research Foundation of Kenya Annual Report 1991, pp 118-119;Owuor PO. 1993. Attempts to understand and prove small-holder tea quality through agronomic practices.Proceedingsof the Policy and strategy Workshop for KTDA Board of Directors Seminar Safariland Club Ltd, Naivasha, Kenya 2-

5th August; Owuor PO. 1993. Comparative studies on black tea quality and chemical composition of different varietiesand clones ofCamellia sinensis in Kenya: review. Tea, 14, 54-60; Owuor PO. 1993. Varietal and clonal chemicalcomposition and quality variations of black tea Camellia sinensis (L) in Kenya.Proceedings of inaugural conference of

Kenya Chemical Society. University of Nairobi. 7-11th June, pp 71-73.

73 17270; 234425; 18998; 243661; 246141; Mahanta PK, Barua S, Owuor PO, Murai T. 1988. Flavour volatile of

Assam black teas manufactured from different plucking standards and orthodox teas manufacture from differentaltitudes of DarJeeling. J.Sci.Food Agric.45, 317-324; Owuor PO. 1995. Improving the quality of plain black tea byagronomic practices.Proceedings of Regional Tea Research Seminar; Blantyre . Malawi, 21- 23rd March; Owuor PO,Obanda MA, Tsushida T, Horita H, Murai T. 1987. Geographical variations of theaflavins, thearubigins, caffeine inKenya clonal black tea.Food Chemistry,26, 223-230.

7414884; 13414; Obanda M, Owuor PO. 1993. The correlation of total polyphenols content in fresh tea shoots, plain

black tea quality parameters and tasters preferences of AHP clones. Tea Research Foundation of Kenya Annual Report,pp 132,137-138; Obanda M, Owuor PO. 1994. Clonal variation of total polyphenols contents in green leaf and blacktea quality. Tea Research Foundation of Kenya Annual Report 1994 , pp 96-100.

75244249; Owuor PO. 1983. Miniature manufacture for plant improvement. Tea Research Foundation of Kenya

ANNUal Report 1983, pp 13-20; Owuor PO. 1984. Miniature manufacture for plant improvement. Tea ResearchFoundation of Kenya Annual Report 1984. pp 60-64; Owuor PO. 1988. Clonal selection through quality.Tea ResearchFoundation of Kenya Annual Report 1988, pp 54-55; Owuor PO. 1989. Clonal selection through quality. TeaResearch Foundation of Kenya Annual Report 1989pp 81-82; Owuor PO. 1990. Assessment of quality of some clonesunder test. Tea Research Foundation of Kenya Annual Report 1990pp 89-90.

8/22/2019 Vol 26 13 Quality

21/32

76Owuor PO. 1993. Impact of individual theaflavins levels on astringency of black tea. Tea Research Foundation of

Kenya Annual Report 1993, pp 96-102; Owuor PO, Obanda M. 1995. Changes in Astringency of Black Tea Due toVariations in Individual Theaflavin Levels. Proceedings of `95 International Tea Quality Human health Symposium.Shanghai, China, 7-10th Nov. 1995. pp 201-205; Owuor PO, Obanda M. 1995. Clonal Variation in the IndividualTheaflavin and Their Impact on Astringency and Sensory Evaluation. Food Chem.54, 273-277; Owuor PO, ObandaM. 1995. Towards reliable plain black tea quality parameters: Individual theaflavins. Proceedings of the Kenya

Institute of Food Technologists Conference. Serena Hotel, Nairobi, Kenya, 6-8th Nov., 1995.

77Taylor S, Baker D, Owuor P, Orchard J, Othieno C, Gay C. (1992). Model for predicting black tea quality from the

carotenoid and chlorophyll composition of fresh green leaf. J. Sci. Food Agric.58, 185-189; Taylor S, Owuor PO,Gay C. 1991. Predicting black tea quality from plant pigment composition of fresh green leaf using a multipleregression model: Effect of season on predictive performance. In Contribution of Tea Science to Human Health:

Proceedings of International Symposium on Tea Science. Shizuoka, Japan 26-29th Aug. pp 120-124; Taylor SJ,Owuor PO. 1991. Natural Resources Institute-Tea Research Foundation of Kenya Collaborative project. Tea Research

Foundation of Kenya Annual Report 1991, pp 120-121.

78Obanda M, Owuor PO. 1993. The correlation of total polyphenols content in fresh tea shoots, plain black tea quality

parameters and tasters preferences of AHP clones. Tea Research Foundation of Kenya Annual Report, pp 132,137-138;Obanda M, Owuor PO. 1994. Clonal variation of total polyphenols contents in green leaf and black tea quality. Tea

Research Foundation of Kenya Annual Report 1994, pp 96-100; Obanda M, Owuor PO, Taylor SJ. 1995. Flavanol

Composition And Caffeine Content of Green Leaf as Quality Potential Indicators of Kenyan Black Teas.Proceedings ofthe Kenya Institute of Food Technologists Conference . Serena Hotel, Nairobi, Kenya, 6-8th Nov., 1995.

79Robinson JM, Owuor PO. 1992. Tea aroma. In "Tea Cultivation to consumption, (Wilson KC. and Clifford MN.

Eds). Chapman and Hall, London, 1st edition, chapter 18, pp 603-642; Robinson JM, Owuor PO. 1993. Tea: Analysisand tasting. In " Encyclopedia of Food Science, Food Technology and Nutrition". (MacRea R, Robinson R and SaddlerM. Eds). Academic Press. Vol.7, pp 4537 - 4542.

80Owuor PO. 1995. Improving the quality of plain black tea by agronomic practices. Proceedings of Regional Tea

Research Seminar; Blantyre. Malawi, 21- 23rd March.

81Owuor PO, Odhiambo HO. 1991. Response of black tea chemical quality parameters of two tea varieties to methods

and frequencies of harvesting Tea Research Foundation of Kenya Annual Report 1991, pp 118, 120-122; Owuor PO,Odhiambo HO. 1993. The response of quality and yield of black tea of two Camellia sinensis varieties to methods andintervals of harvesting.J. Sci. Food Agric.62, 337-343.

82Owuor PO, Odhiambo HO. 1991. Response of black tea chemical quality parameters of two tea varieties to methods

and frequencies of harvesting Tea Research Foundation of Kenya Annual Report 1991, pp 118, 120-122; Owuor PO,Odhiambo HO. 1993. The response of quality and yield of black tea of two Camellia sinensis varieties to methods andintervals of harvesting. J. Sci. Food Agric. 62, 337-343.

83233565; Owuor PO, Njuguna CK. 1991. Characteristics of chemical quality parameters of black tea from different

varieties and their response to method of manufacture. Tea Research Foundation of Kenya Annual Report 1991, pp118-119.

84 233565; Owuor PO. 1993. Comparative studies on black tea quality and chemical composition of different varieties

and clones ofCamellia sinensis in Kenya: review. Tea, 14, 54-60; Owuor PO. 1993. Varietal and clonal chemicalcomposition and quality variations of black tea Camellia sinensis (L) in Kenya.Proceedings of inaugural conference of

Kenya Chemical Society. University of Nairobi. 7-11th June, pp 71-73; Owuor PO, Njuguna CK. 1991.Characteristics of chemical quality parameters of black tea from different varieties and their response to method ofmanufacture. Tea Research Foundation of Kenya Annual Report 1991 , pp 118-119.

8506686; Owuor PO. 1987. Variations in theaflavins contents and tasters evaluation of grafted teas. Tea Research

Foundation of Kenya Annual Report 1987, pp 77-78; Bore JK, Njuguna CK, Owuor PO. 1995. Chip-Budding in Tea(Camellia Sinensis (L.) O. Kuntze) and Its Effects on Yields and Quality. Tea, 16, 9-13.

8/22/2019 Vol 26 13 Quality

22/32

8617272; 201852; 202379; 234258; 241665; Mahanta RK, Baruah S, Owuor PO, Murai T. 1988. Flavour volatiles of

Assam black teas manufactured from different plucking standards and orthodox teas manufacture from differentaltitudes of Derjeeling.J. Sci. Food Agric.45 317-324; Obanda AM, Owuor PO. 1991. Effect of wither and pluckingon biochemical and chemical parameters of a selected Kenyan Tea. Tea Research Foundation of Kenya Annual Report1991, pp 127-132; Obanda M. 1993. Comparison of volatile formation due to shoot part manufacture and pluckingstandard. Tea Research Foundation of Kenya Annual Report 1993, pp 114-115; Obanda M, Owuor PO. 1994. Theeffect of wither and plucking standard on biochemical and chemical parameters of selected Kenya tea, Discovery and

Innovation, 6, 190-197; Obanda M, Owuor PO. 1994. Effect of Shoot Maturing and Process on the ResidualChlorophyll Content, Composition of Volatile Flavour Compounds and Plain Black Tea Chemical Quality Parameters.

Proceedings of Kenya Institute of Food Technologists Conference, Serena Hotel, Nairobi, 7-9th November, 1994 (OjijoNKO, Mathooko FM, Koaze H, Wongo LE. Eds) pp 59-64; Owuor PO. 1987. Nitrogenous fertilizer rates and pluckingstandards effects on chemical composition and quality of CTC black tea. Proceedings of International Tea Symposium26-28th June, Rize, Turkey. pp 111-123; Owuor PO. 1989. Changes in the unsaturated fatty acids and total fatty acidswith plucking standards. Tea Research Foundation of Kenya Annual Report 1989 , pp 106, 108; Owuor PO. 1989.Distribution of fatty acids in different parts of the shoots. Tea Research Foundation of Kenya Annual Report 1989 , pp106-107; Owuor PO. 1994. Improving black tea quality through optimum plucking. Proceedings of InternationalSymposium on Plantation crops, 30 th Nov- 3rd Dec. Calicut, Kerala; Owuor, PO, Munavu RM, Muritu JW. 1990.Plucking standards effects and distribution of fatty acids in tea (Camellia sinensis (L.)) leaves.Food Chemistry,37, 27-35; Owuor PO, Obanda M. 1991. Effect of plucking standards and fermentation time on black tea manufacture andquality. Tea Research Foundation of Kenya Annual Report 1991, pp 123-127; Owuor PO, Obanda M. 1992. Theeffect of plucking standards and fermentation duration on black tea quality of clone 6/8. Tea Research Foundation of

Kenya Annual Report 1992, pp 80-82; Owuor PO, Obanda M. 1994. Variations in the Catechins Levels and the PlainBlack Tea Quality Parameters Due to Plucking Standards and Fermentation Duration. Proceedings of the Kenya

Institute of Food Technologists Conference. Serena Hotel, Nairobi, Kenya, 7-9th Nov., 1994, (Ojijo NKO, MathookoFM, Koaze H, Wongo LE. Eds) pp 65-70; Obanda M, Owuor PO. 1995. Impact of Shoot Maturity on ChlorophyllContent, Composition of Volatile Flavour Compounds and Plain Black Tea Chemical Quality Parameters of ClonalLeaf. J. Sci. Food Agric. 69, 529-534; Obanda MA, Owuor PO. 1995. Clonal Variation in Chemical QualityParameters and Tasters' Evaluation of Black Tea Due to Green Leaf Plucking Standards. Food Chem. 53, 381-384;Owuor PO. 1991. Correct plucking standard and intervals for optimum quality. In "Improving Tea ManufactureThrough Research". Proceedings of Seminar For Small-Holder Tea Factory Managers , (Othieno CO, Owuor PO,Orchard JE. eds), Tea Research Foundation of Kenya, Kericho. 15th-16th and 22nd-23rd January 1991. pp 33-37;Owuor PO. 1994. Improving black tea quality in Kenya through optimum plucking. Proceedings of InternationalSymposium on Plantation Crops (PLACROSYM XI), Calicut, Kerala, India, 30th Nov.-3rd Dec. 1994.

87Othieno CO. 1988. Summary of recommendations and observations from Tea Research Foundation of Kenya. Tea,9,

50-65.

88Obanda M, Owuor PO. 1993. Variation in clonal black tea chemical quality parameters and tasters' evaluation's due togreen leaf plucking standards. Tea Research Foundation of Kenya Annual Report 1993, pp 111, 113-114; Obanda M,Owuor PO. 1994. The effect of wither and plucking standard on biochemical and chemical parameters of selectedKenya tea,Discovery and Innovation,6, 190-197; Obanda M, Owuor PO. 1994. Effects of shoot maturing process onthe residual chlorophyll content, composition of volatile flavour components and plain black tea parameters.

Proceedings of Kenya Institute of Food Technologists Conference. Serena Hotel, Nairobi, Kenya, 7-9th Nov; ObandaM, Owuor PO. 1995. Clonal variation in chemical quality parameters and tasters evaluation of black tea due to greenleaf plucking standards.Food Chem.53, 381-384.

89Owuor PO, Obanda M. 1994. Comparison of the effect of fermentation duration and plucking standards on the

astringency of two clonal black tea. Tea Research Foundation of Kenya Annual Report 1994 , pp 106.

90 01758; 06599; 18995; 200063; 241672; 241676; Owuor PO. 1993. Effect of plucking intervals and nitrogenous

fertilizers on clone S 15/10 quality. Tea Research Foundation of Kenya Annual Report 1993, pp 110, 112; Owuor PO.1994. Effect of plucking intervals and nitrogenous fertilizers on clone S15/10 black tea quality. Tea Research

Foundation of Kenya Annual Report 1994, pp 100-101.

91 200063; 241672; Ngetich WK, Odak JO, Othieno CO. 1993. Plucking frequencies and nitrogen rates on clone S

15/10, Kaproret Estate. Tea Research Foundation of Kenya Annual Report 1993 , pp 163-164; Ngetich WK, Othieno,CO, Odak JO. 1993. Nitrogen rates and plucking frequency of tea. Timbilil Estate. Tea Research Foundation of

Kenya Annual Report 1993, pp 163; Odhiambo HO. 1987. Effect of nitrogen rates and frequency of plucking on the

8/22/2019 Vol 26 13 Quality

23/32

components of yield of tea. Tea Research Foundation of Kenya Annual Report 1987, pp 19-22; Odhiambo HO. 1988.The effect of nitrogen rates and plucking frequency on the components of yield of tea. Tea Research Foundation of

Kenya Annual Report 1987, pp 12 -15; Odhiambo HO. 1989. Effect of nitrogen rates and plucking frequency on thecomponents of yield of tea. Tea Research Foundation of Kenya Annual Report 1989 pp 11-12; Odhiambo HO. 1990.The effect of nitrogen rates and plucking frequency on tea yields and yield components. Tea Research Foundation of

Kenya Annual Report 1990, pp 10-11; Odhiambo HO. 1991. Nitrogen rates and plucking frequency on tea. TimbililEstate. Tea Research Foundation of Kenya Annual Report 1991, pp 14-16; Odhiambo HO. 1991. Effects of fertilizerrates and plucking frequencies on yield components of clones S15/10. Kaproret Estate. Tea Research Foundation of

Kenya Annual Report 1991. pp 16-17; Odhiambo HO. 1992. Nitrogen rates and plucking frequency of tea. TimbililEstate. Tea Research Foundation of Kenya Annual Report 1992 pp 14-15; Odhiambo HO. 1992. Plucking frequenciesand nitrogen rates on clone S15/10, Kaproret Estate. Tea Research Foundation of Kenya Annual Report 1992 pp 15-16.

92Owuor PO. 1993. Effect of plucking intervals and nitrogenous fertilizers on clone S 15/10 quality. Tea Research

Foundation of Kenya Annual Report 1993, pp 110, 112; Owuor PO, Odhiambo HO. 1994. Response of some blacktea quality parameters to nitrogen fertilizer rates and plucking frequencies. J. Sci Food Agric, 66, 555-561.

93Owuor PO, Odhiambo HO. 1991. Response of black tea chemical quality parameters of two varieties of tea to methods

and frequency of harvesting. Tea Research Foundation of Kenya Annual Report 1991, pp, 118, 120-122; Owuor PO,Odhiambo HO. 1993. The response of quality and yield of black tea of two Camellia sinensis varieties to methods andintervals of harvesting.J. Sci. Food Agric.62, 337-343.

94584; Ndamugoba D. 1977. Harvesting tea by machine