EFFECT OF FAR-INFRARED HEATER ON THE PHYSICOCHEMICAL CHARACTERISTICS OF GREEN TEA DURING PROCESSING

Abstract

ABSTRACT The green tea leaves (Camellia sinensis var. sinensis) were irradiated by a far-infrared (FIR) heater during the roasting and drying step, resulting in three different treatments produced. Green tea was extracted by soaking the leaves in water, and the components were analyzed. FIR irradiation, combined with fryer heating during the roasting step and additionally applied after the drying step, increased total phenolic contents of green tea from 116.30 to 171.77 mg/g, and total flavanol contents from 17.54 to 24.76 mg/g, compared with the non-irradiated control. Ascorbic acid contents also increased from 3.07 to 4.20 mg/g. The amounts of epicatechin gallate and epigallocatechin gallate were significantly increased from 2.41 to 4.59 mg/mL and 20.61 to 28.54 mg/mL, respectively, compared with the non-irradiated control. FIR irradiation increased Nitrite Scavenging Ability of green tea at pH 3.0 and pH 4.2, while there was no significant difference at pH 6.0. Sweetness, umami and aroma of green tea were enhanced by FIR irradiation, while bitterness and astringency were decreased compared with those of the control. These results show that FIR heating during the green tea process affected the chemical properties of green tea, and the FIR heater can be applied to increase the physicochemical qualities of green tea. PRACTICAL APPLICATIONS Green tea, a widely consumed drink, has received much attention because of the beneficial biological effects attributable to its excellent antioxidant activity. In this article, a far-infrared (FIR)-heater for industrial application was used during the processing of green tea leaves, and the chemical characteristics and quality of FIR-treated green tea were determined. FIR irradiation, combined with fryer heating during the roasting step and additionally applied after the drying step, significantly increased phenolic, flavanol, ascorbic acid, epicatechin gallate, epigallocatechin gallate contents and nitrite-scavenging activity compared with non-irradiated control. Sensory evaluation also showed a positive effect of FIR irradiation. The results indicated that FIR heater could be easily applied to increase the quality of green tea in the processing line.