Effects of processing conditions on change of amino acids, reducing sugar and total polyphenols of caramelized malt produced from IR50404 rice variety

Rice beer is a value-added product from rice since it consists of enough conditions for making beer. To produce the best caramelized malt from IR50404 rice variety, understanding the effects of processing conditions on change of amino acids, reducing sugar and total polyphenols is very important for developing such rice beer processing. Changes in chemical compositions and enzyme activities in caramelized malt processed from IR50404 rice variety were understood. Suitable germination conditions were indicated, including a soaking temperature of 30oC for 24 hrs, degree of steeping of 35- 36% and germination time of 4 days at 30oC. Green rice malt was incubated at 40-70oC for 30-120 mins. Then, rice malt was roasted at different temperatures of 125-200oC for 30-90 mins. The results showed that both tempering and roasting processes changed the concentration of polyphenols, reducing sugars and amino acids. When green malt was incubated at 50°C for 60 mins, reducing sugars, amino acids and polyphenol content (TPC) increased by 2 times (102.72 mg/g), 1.8 times (9.08 mg/g) and 1.5 times (4.26 mg GAE/g) respectively corresponding to the improvement of the amylase and protease activity. Moreover, there were maximum increases in phenolic compounds in roasted malt at 125 and 150°C for 45 and 75 mins for tempered malt and green malt, respectively. In contrast, higher heat treatment (roasted at 175-200°C) resulted in reducing the levels of all evaluated variables. Thus, malting with a moderate thermal treatment (125-150°C) could be considered an effective process to enrich (or enhance) antioxidants in rice grains for their further use as a functional ingredient in malt and beer production.