Using endogenous pigments to recolour roasted green tea

Abstract

Roasted green tea exhibits undesirable dark green that can seriously affect sensory quality, market price, and consumer acceptance. The aim of this work was to propose a method of improving the appearance of the roasted green tea. In this study, rehydration with freeze-drying (RFD) was used to recolour the tea leaves by redistributing the endogenous pigments. The results indicated that the colour of the roasted green tea changed from dark green to bright green after the RFD treatment, the values of L∗ and b∗ were significantly increased (P<0.05), and the value of a∗ was significantly decreased (P<0.05). In addition, the RFD treatment making the yellow-green pigments transfer onto the surface of the tea leaves also induced a change in pigment contents, including chlorophylls, carotenoids, and flavonoid glycosides. The well-defined optimum parameters for the rehydration process were moisture content of tea leaves at 35 per cent, water temperature 25 °C, and a standing time of 1.5 h.