Extractability of tea catechins as a function of manufacture procedure and temperature of infusion

Abstract

Green teas were made by different inactivation procedures ranging from steaming, thermal inactivation by heating in an oven or microwave-mediated inactivation, followed by either unidirectional or bi-directional rolling and drying. Teas were infused at different temperatures (80 and 100 °C) and the tea ceremony way of infusing, and analyzed for tea catechins and xanthine alkaloids by HPLC. Teas manufactured following microwave inactivation, bi-directional rolling and drying showed higher catechins and methyl xanthines by HPLC, and extracted higher catechins and caffeine in infusions. Catechins, especially EGCG, EGC, and EC, showed marked differences when extracted at different temperatures. Considerable amounts of catechins and caffeine can be extracted each time when the same leaf is infused repeatedly 4–5 times, as done in Japan for making ceremonial teas.

Introduction

Tea is a processed product of the leaves of Camellia sinensis. The shoots, consisting of tender apical bud and subtending three leaves, are processed to give the tea, which upon infusion with hot/cold water gives a non-alcoholic beverage. Tea shoots are rich in catechins, and the ratio and quantity of these determine the taste and quality of the teas. Tea is manufactured as non-fermented green tea, semi fermented oolong tea and fermented black tea (Lin, Lin, Liang, Lin-Shiau, & Juan, 1998). Green teas or non-fermented teas are characterized by inactivation of the enzyme polyphenol oxidase immediately after plucking of the tea shoots. This enzyme is responsible for oxidizing the catechins to theaflavins and thearubigins, the tea pigments responsible for the colour and taste of black teas. The inactivation can be achieved by either parching, roasting or steaming the tea shoots. Traditionally, Chinese people roast the tea shoots in a metal roaster and process the tea shoots by using a unidirectional rotatory roller. This type of rolling gives a twist to the leaf and compacts the particles. The Chinese green tea is characterized by a roast odour. On the other hand, the Japanese inactivate the tea shoots by steaming, followed by bi-directional rolling. This rolling makes the shoot surface flat with leaf juice spread over the entire surface. Green tea is gaining popularity because of its medicinal properties that range from anticancer to antiulcer (Jankun et al., 1997, Sakanaka et al., 1989, Yang, 1997). These pharmacological properties are mainly due to the presence of catechins which constitute up to 30% on a dry weight basis, are water-soluble and can be easily extracted in infusions. The amount of catechins extracted depends upon the genetic characters, the manufacture style and the temperature of infusion. This paper presents the effect of different styles of manufacture on infusion characteristics, mainly extractability of catechins into the infusion, the importance of repeated extraction on the amount of catechins extracted into the infusion at different temperatures and amount of catechins extracted into successive cups of extracts consumed in the traditional ceremonial teas.