Optimization of enzymatic hydrolysis of immature citrus (Citrus unshiu Marcov.) for flavonoid content and antioxidant activity using a response surface methodology.

Immature citrus with peel was enzymatically treated for production of a hydrolysate with enriched bioactive components and higher antioxidant activity. The effects of reaction factors, including enzyme concentration, reaction time, and temperature on hesperetin and naringenin contents, total phenolic content (TPC), and antioxidant activity were investigated using response surface methodology. The models were adequate, and the enzyme concentration, temperature, and time positively affected hesperetin and naringenin contents and TPC, but negatively affected DPPH radical scavenging capacity. The reaction conditions for maximizing hesperetin, naringenin, and total phenol production and ferric reducing antioxidant power were optimized with the combination of enzyme concentration at 4%, 51 °C and 18 h. The hydrolysate at the optimized conditions contained higher hesperetin and naringenin contents and TPC compared with those before hydrolysis, by 251.7-, 45.5-, and 2.6-fold, respectively. This hydrolysate can be utilized in the production of functional beverages with high added values. © The Korean Society of Food Science and Technology 2021.