Study on preparation technology, antioxidant activity and nitrosation inhibition of brown rice tea

Based on the processing technology of brown rice tea, this study explored the brown rice tea beverage with improved antioxidant capacity under this technology, and the effects of baking temperature, baking time and liquid-material ratio on the polyphenol content of brown rice tea extract were investigated by single factor experiment. Then, the processing technology of brown rice tea was optimized by three-factor and three-level Box-Behnken response surface method, and the best technological conditions were obtained. The optimized brown rice tea extract was compared with V_C solution for its DPPH free radical scavenging ability, hydroxyl free radical scavenging ability, ABTS free radical scavenging ability, reducing power ability and ability to inhibit nitrite and nitrosamine synthesis blocking. The results showed that the polyphenol content was the highest when the baking temperature was 180℃, the baking time was 20 min and the ratio of liquid to material was 20:1. In the response surface regression equation, the determination coefficient R² was 0.986 8, and the correction coefficient R²_Adj was 0.969 8. The difference between them was less than 0.2, which indicated that the model had a high fitting degree and a small error. The degree of influence of three factors on polyphenol content was baking temperature (A) > liquid-material ratio (C) > baking time (B). Under the conditions of baking temperature 186.22℃, baking time 30.40 min and liquid-material ratio 21.89:1(mL/g), the software predicted that the polyphenol content of brown rice tea extract was 38.25 μg/g, and the modified optimum extraction conditions were baking temperature 186℃, baking time 30 min, and the ratio of liquid to material 22:1 mL/g. Under these conditions,the results showed that the polyphenol content reached 39.38 μg/g. The scavenging rates of DPPH radical, hydroxyl radical, ABTS radical and reducing power of brown rice tea extract were 86.5%, 60.8%, 90.2% and 0.39 respectively. The nitrite clearance rate of brown rice tea extract was 65.0%, and the blocking rate of nitrosamine synthesis was 48.51%. High temperature baking improved the polyphenol content and antioxidant capacity of brown rice tea extract to a certain extent, and the optimized brown rice tea extract had good antioxidant capacity and a certain ability to inhibit nitrosation.