Enhancing the quality of naturally oxidized tea with ascorbic acid

Abstract

Tea globally the most popular refreshing beverage, processed from the leaves of Camellia sinensis is evaluated organoleptically. While the biochemical potentials are fixed in the leaves, it is made palatable through processing. But for the rich polyphenols and caffeine in tea, it would not have been a beverage. Catechins are about two thirds of polyphenols undergo oxidation in the presence of the polyphenol oxidase to produce polyphenolic pigments namely theaflavins (TF), thearubigins (TR) and other polymerization compounds. The level of these compounds and their balance in the tea liquor determine the quality of black tea. Among these theaflavin plays a pivotal role and is directly proportional to the quality of liquor. Hence, an attempt has been made to increase the theaflavin levels and other quality attributes of the liquor through addition of ascorbic acid. Native level of ascorbic acid is very less in tea leaves and negligible in processed tea. Ascorbic acid when added during oxidation process reacts with catechins to produce stable secondary polyphenols. Ascorbic acid addition increases the formation of theaflavins from 1.23 to 1.77%. Moreover further polymerization of polyphenols to other undesirable complexes is arrested due to reduced oxygen uptake. Ascorbic acid addition at optimum level does not change the inherent quality and related attributes of the tea liquor. The stability and total liquor colour of the liquor is increased from 3.82 to 4.72%. As increasing the native level of ascorbic acid is difficult, external addition of ascorbic acid in processing is to be explored. The pH and EC value does not change up to addition of 2500 ppm concentration of ascorbic acid. Addition of ascorbic acid is enhancing the overall quality of black tea at concentration of 2500 ppm. Ascorbic acid is also being a tool in biosynthesis of several secondary polyphenols such as theaflavins thearubigin.