[4-1015-D] Food Quality (1)

[4-1015-D-06] Processing of Green Tea Paste by Micro Wet Milling and Quality Evaluation During Storage

*Md Zohurul Islam¹, Yutaka Kitamura¹, Mito Kokawa¹, Shinya Fujii², Hisayuki Nakayama² (1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Tsukuba-shi, Japan(Japan), 2. Nagasaki Agricultural and Forestry Technical Development Center, Nagasaki, Japan(Japan))

Keywords:Green Tea Paste, MWM, Color, Antioxidants, Storage study, Kinetic model

Green tea is a delicious variety of tea that is made from the Camellia sinensis plant. It is a non-fermented tea, thus contain higher amounts of phytochemicals, alkaloids, polyphenols including EGCG compared with black tea and oolong tea. In this regard there is increasing interest in its health benefits has led to the inclusion of green tea in the processing of value-added products with functional properties. But there are challenges to add green teas into the process product due to the higher particle sizes and insolubility in cold water. Therefore, the aim of the present study was to develop green tea paste by micro wet milling system with minimum particle sizes which lead to increase solubility and enhance bioactive compounds. In the present study, three varieties of green tea samples Yabukita (shaded) Yabukita (non-shaded) and Hoji cha were collected from Nagasaki, Japan. The green tea paste was produced by MWM. The wet milling conditions were set by varying the green tea to water ratio (10:90; 15:85; and 20:80 w/w), feeding rate (15 mL/min to 25 mL/min) and constant rotational speed of 50 rpm for the preparation of green tea paste. The optimum milling conditions were determined based on achieving minimum particle sizes. Feeding rate 20 mL/min, green tea to water ratio of 20:80 w/w, and rotational speed 50 rpm can able to produce paste with smaller average particle sizes of 58.64±2.31 µm with better color (in terms of greenness and chroma value) and nutrition properties (i.e. ascorbic acid, polyphenol, and antioxidants). To evaluate the shelf life and storage stability, three kinds of green tea paste were stored at 20 °C, 4 °C, -18 °C and -60 °C with vacuum packing for 4 weeks. Temperature and storage time negatively influenced the stability of ascorbic acid, color, and antioxidant activity during storage. A kinetic study of the green tea paste was conducted to quantify the losses occurring in ascorbic acid, antioxidant activity and changes in the color of the green tea paste. The study revealed that the logistic model can predict the variation in ascorbic acid and antioxidant activity with higher R² = 0.98 value. However, first-order kinetic models were found suitable to predict the changes occurring in ascorbic acid, antioxidant activity and color properties (L, a, b, chroma). Whereas the total color changes (ΔE) showed a good fit with zero order kinetic models (R² = 0.98). So we concluded that we can preserve the green tea paste at a lower temperature by keeping minimum losses of color and antioxidant properties. Before commercialization, a sensory and microbial study needs to be carried out in the future.