Response surface optimization of active peptides of Rana spinosa ( Quasipaa spinosa ) meat process and evaluation of immunomodulatory activity

Rana spinosa is a high-quality source of animal protein, which is a traditional Chinese ingredient with edible and medicinal properties. However, with the expanding scale of Rana spinosa farming in China, little research has been done on its deep processing and bioactivities. In this study, we optimized the enzymatic hydrolysis process of Rana spinosa meat and investigated the amino acid composition, degree of hydrolysis, and immunomodulatory, and antioxidant activity of active peptides of Rana spinosa meat. The results showed that the optimal enzymatic hydrolysis conditions of active peptides of Rana spinosa meat were neutral protease hydrolysis for 2.5 h, temperature 40 °C, pH 7.2, and enzyme-to-substrate ratio 0.4%. The active peptides of Rana spinosa meat obtained under these conditions were rich in essential amino acids (34.091%) and hydrophobic amino acids (32.932%), and the degree of hydrolysis of protein and the proliferation rate of RAW 264.7 cells were 28.1% and 147.06%. At 2000 μg/mL, the peptides had significant proliferative activity (233.5%), and phagocytic activity (216.9%), and promoted NO released (23.2 pg/mL), IL-6 (635.4 pg/mL, and TNF- α (1001.3 pg/mL), which were 2.33, 2.16, 7, 24.57, and 6.91 times higher than the blank control group, respectively. In addition, the optimal peptides showed good ABTS radical scavenging activity (IC 50 : 263 μg/mL) and Fe 2+ chelating activity (EC 50 : 1047 μg/mL). Therefore, the active peptides of Rana spinosa meat might become potential raw materials for natural immunomodulators and antioxidants, and provide process parameters and a theoretical basis for the further processing and high-value utilization of Rana spinosa .