Slit divergent ultrasound pretreatment assisted watermelon seed protein enzymolysis and the antioxidant activity of its hydrolysates in vitro and in vivo.

Watermelon seed, a watermelon processing industry by-product, is a good protein source for the preparation of antioxidant peptides due to its high protein content, low cost, special amino acid composition. Antioxidant hydrolysates obtained from watermelon seed protein (WSP) after slit divergent ultrasound (SDU) treatment were studied. The stepwise multiple linear regression model verified that the reducing power of watermelon seed protein hydrolysates (WSPHs) is positively related with -SH and β-turn content of WSP (R = 0.931, p < 0.01). Using the degree of hydrolysis (DH) and reducing power as indicators, the WSPHs was prepared under the optimal conditions (ultrasound frequency: 20/28 kHz, time: 60 min, power density: 100 W/L) and divided into three components by ultrafiltration membrane (1 and 5 kDa). Compared with WSPHs and other fractions, WSPHs-I (Mw < 1 kDa) not only significantly protected HepG2 cells from HO-induced damage, but also greatly alleviated the liver injury caused by d-galactose in male SD rats.