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.
[Advances in the use of instrumental measurement of colour in the development, production and quality control of drugs, medicinal preparations and pharmaceutical auxiliary substances II*].
The paper summarizes the use of instrumental colour measurement in the field of pharmaceuticals of natural origin and other substances of natural origin beneficial for health in recent 10 years. Colour measurement in this field was most frequently employed in the monitoring of various aspects of the process of drying of medicinal plants and their parts.
The effect of temperature on enzyme activity during the fermentation phase of black tea manufacture
Activities of both polyphenoloxidase and peroxidase enzymes declined as a function of fermentation time, the magnitude of the effect on the former being much greater. The effect of temperature on the rate of inactivation was also much greater on polyphenoloxidase.