Estimation of tea quality by infusion colour difference analysis
The colour differences in terms of deltaL, deltaa, deltab and deltaE between distilled water and infusions of 29 green teas, 16 black teas and 13 oolong teas and their correlation with sensory quality attributes of tea were investigated. The results showed that the deltaL value decreased but the deltaa, deltab and deltaE increased with the degree of fermentation of the three kinds of tea. The deltaL was positively correlated to quality attributes of green tea and oolong tea but negatively correlated to those of black tea. The deltaa of tea infusions is a reliable descriptor to differentiate among green and black teas. The regression of total quality score of green tea (TQSg) upon the deltaa was TQSg = -2.26deltaa + 77.2 (R2 = 0.22, p < 0.01), that of total quality score of black tea (TQSb) upon deltab was TQSb = 0.70deltab + 44.6 (R2 = 0.31, p < 0.05) and that of total quality score of oolong tea (TQSo) upon deltaL was TQSo = 1.09deltaL + 94.5 (R2 = 0.75, p < 0.01). Because the infusion colour difference indicators of deltaa, deltab and deltaL can be done rapidly, it could be very useful for on-site or on-line quality monitoring during tea manufacture and storage.
Effect of different extracting methods on quality of Chrysanthemum Morifolium Ramat. Infusion.
The flower of Chrysanthemum Morifolium Ramat. (CM) is a useful food and folk medicine in China. Effects of Chrysanthemum Morifolium extracting (CME) conditions, including extraction temperature, extraction time and the ratio of flower to water on infusion quality were investigated. The extractability, liquor color differences and the major flavonoids of luteolin-7-O-beta-D-glucoside and luteolin of various CME methods were evaluated. The results indicated that CME temperature was the most important factors affecting quality of CM infusion. Based on the extractability and chemical compositions, the best CME conditions were the 90 to approximately 100 degrees C, 20-30 min and the ratio of flower to water of 1:40 (w/v). High-performance liquid chromatography (HPLC) of Chrysanthemum Morifolium chemical compositions including luteolin-7-O-beta-D-glucoside and luteolin was also discussed in the present paper.
Estimation of theaflavins in tea by gas—liquid chromatography of their trimethylsilyl ethers
Abstract A method for separating and estimating the theaflavins of tea by temperature-programmed gas—liquid chromatography of their trimethylsilyl ethers is described. 6-in. columns of 3 % OV-1 on Chromosorb W separate theaflavin from its two monogallates and its digallate, and used with a 1,3-distearin standard, give results reproducible to within ± 5 %. Fractions suitable for analysis are obtained by chromatography of ethyl acetate extracts of whole tea solubles on Sephadex LH-20. This method gives lower results than R oberts' spectrophotometric method: chromatograms of acetate extracts before and after bicarbonate extraction suggest that this is a result of incomplete extraction of thearubigins in the R oberts' method.