Optimization of papain hydrolysis conditions to enhance antioxidant activity in de-oiled garden cress (L. sativum) seed protein: response surface methodology approach and hydrolysate characterization

The aim of the present study was to isolate the protein concentrates from garden cress (L. sativum) seeds and to optimize the hydrolysis condition for preparing garden cress protein hydrolysate (GCPH) using response surface methodology (RSM). The effects of hydrolysis parameters, including enzyme-to-substrate (E/S) ratio, pH, and temperature on the degree of hydrolysis (DH%) and antioxidant activity, were also determined and validated. The optimized values of hydrolysis parameters, i.e., E/S ratio, pH, and temperature, were observed to be 1:15, 6.0, and 52.3 °C, respectively. Under the optimum condition, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, ferric reducing antioxidant power (FRAP), and DH (%) were 7.36 ± 0.51, 54.72 ± 1.12 µM TE/mg protein, and 9.59 ± 0.79%, respectively. The functional properties, including oil holding capacity, color values, emulsifying, and foaming properties, were significantly higher (p < 0.05) for GCPH as compared to garden cress protein concentrate (GCPC). In addition, the hydrolysis parameters significantly altered the secondary structure of the protein, resulting in a decreased crystalline structure of the protein hydrolysate. Furthermore, a significant reduction in the particle size of GCPC from 69.8 to 6.17 µm was also observed. Therefore, the findings of this study suggest that garden cress seed protein is a potential source of protein hydrolysate, which can be utilized as a bioactive functional ingredient in food systems for the development of functional foods.