The Optimization of Viscozyme-Assisted Hydrolysis to Enhance Protein Extraction from VD20 Broken Rice: A Response Surface Approach for Functional Health Applications

This study investigated and optimized the cellulose hydrolysis conditions of VD20 broken rice flour using Viscozyme to enhance protein content and protein recovery efficiency. Four processing variables, including pH (5.0–6.0), temperature (40–60 °C), enzyme concentration (20–40 U/g), and hydrolysis time (34–38 h), were simultaneously evaluated using response surface methodology. The results indicated that temperature, enzyme concentration, and hydrolysis time influenced protein release and recovery, whereas pH had a limited effect within the studied range. All variables exhibited nonlinear effects, with distinct optimal regions beyond which protein extraction efficiency declined. The maximum protein content of approximately 77% was obtained at a pH of 5.56, temperature of about 55 °C, enzyme concentration of 30 U/g, and hydrolysis time of 36 h. In contrast, the highest protein recovery efficiency of approximately 54–55% was achieved at a pH of 5.53–5.57, temperature of about 53 °C, enzyme concentration of about 30 U/g, and hydrolysis time of about 36 h. Simultaneous optimization of both responses identified balanced conditions at a pH of about 5.53, temperature of about 53 °C, enzyme concentration of about 29 U/g, and hydrolysis time of about 36 h, yielding protein content of approximately 76–77% and protein recovery efficiency of about 55%. These findings demonstrate that optimization provides an effective strategy for maximizing protein utilization from VD20 broken rice and support the application of Viscozyme-assisted hydrolysis in the valorization of rice processing by-products.