Response Surface Optimization of Enzymatic Hydrolysis of Purple Rice (Cultivated in Soc Trang, Vietnam) Using Amylases and Formulation of Healthy Rice Milk

Abstract

The purple rice (ST variety) which was cultivated in Soc Trang province, Vietnam was used for this research. The rice starch was hydrolysed by two-step enzymatic using α-amylase and gluco-amylase for making rice milk. The effects of enzyme concentration and time on hydrolysis efficiency (total soluble solid content - TSS) were investigated. The Central Composite Design and Response Surface Methodology were used for the experimental design and results analysis. To improve the quality of rice milk, the effect of five formulations mixture with various milks on sensory attributes and nutritional content were measured. The method of Principle Component Analysis and Check-all-that-apply analysis were applied. The results showed that the optimum enzyme concentration and time ofα-amylase (0.149% and 57 minutes) and gluco-amylase (0.143% and 40.94 minutes) hydrolysis were found as R2 were 0.88 and 0.97, respectively. The maximum TSS production at optimum condition was 16%. For purple rice milk production, formula 4 (70% rice milk, 10% soybean milk, 12% water caltrop milk and 8% sesame milk) was presented better sensory quality than other formulations. The content of protein, carbohydrate, lipid and anthocyanin content of final product were 1.85%, 7.3%, 1.32% and 2.89 mg/L, respectively.