Optimization of brewing, processing conditions and their effects on the chemical and sensory quality of purple-leafed Kenyan tea

Abstract

The Tea Research Institute (TRI) developed TRFK 306 tea clone which is rich in anthocyanin as a strategy to diversify Kenyan teas. TRFK 6/8 was used as a control in the study being a standard clone used at the TRI. TRFK 306 can be utilized non-processed but there is no well researched, documented data on the best brewing conditions. Consumers add edible acids to its brew to improve the colour and taste but information on the acid effect is scanty. Information on the quality of products manufactured in various ways is equally scanty. Completely randomized block design replicated three times was adopted. Fresh TRFK 306 tea leaves were brewed using time temperature combinations of 70 0C and 92 0C timed at 5, 10 and 15 minutes prior to analysing for total anthocyanins and antioxidant activity. Citric acid concentration of 0.1 %, 0.2 %, 0.3 %, 0.4 % and 0.5 % were used to check their effect on total anthocyanins .antioxidant activity and sensory quality. Five- point hedonic scale was used in the sensory evaluation. Non-aerated and aerated orthodox and Crush, Tear and Curl (CTC) teas were processed at different withering times with an interval of 5 hours starting from 0 up to 20 hours. Aeration duration was varied at an interval of 30 minutes, from 30, to 90 minutes. Tea quality parameters were assayed using the Flavognost method, Roberts method, High Performance Liquid Chromatography (HPLC) and UV spectrophotometer. Experienced tea tasters tasted the processed samples subjectively. Data obtained were subjected to general linear model using SAS package version 9.1.3. Means were separated using Least Significant Difference at p < 0.05 significance level. Non-processed purple tea leaves brewed for five minutes using boiling water, had anthocyanins level of 92 mg/L and had over 87.7 % antioxidant activity without citric acid added. Citric acid lowered antioxidant activity though it improved the taste and colour. TRFK 306 non- aerated orthodox teas had more total catechins than CTC teas and best withered for 10-15 hours for higher antioxidant activity. Non- aerated TRFK 306 CTC teas had a score of 3.5 in liquor briskness while TRFK 6/8 teas highest scored was 2. Aerated TRFK 306 CTC teas had a highest theaflavins of 14.41 μmol/g compared to TRFK 6/8 CTC teas with highest value of 16.43 μmol/g. Aerated TRFK 306 orthodox teas had a highest liquor flavour score of 4 slightly lower than TRFK 6/8 orthodox teas with 4.4. It was concluded that, TRFK 306 can be utilized non-processed or can be processed into green orthodox or aerated CTC teas at withering hours not exceeding 15 hours and aeration time not exceeding 60 minutes for premium products. TRFK 306 tea leaves are recommended for direct use without much processing.