Effects of divergent ultrasound pretreatment on the structure of watermelon seed protein and the antioxidant activity of its hydrolysates.

In the present study, the antioxidant hydrolysates obtained from watermelon seed protein (WSP) after divergent ultrasound and ultrafiltration treatment were studied. The results showed that the slit divergent ultrasound (SDU, 20/28 KHz) pretreatment had considerable influence on the structure and enzymatic efficiency of WSP. Besides, compared with hydrolysates without ultrasonic and ultrafiltration treatment, watermelon protein hydrolysates with molecular weight <1 kDa (WSPHs-I) showed the highest antioxidant activities and could protect RAW 264.7 cells from H2O2-induced oxidative stress damage via activating the Nrf2/HO-1 pathway. Interestingly, WSPHs-I had good stability against oxidation at temperature under 100 °C or in the acidic or neutral condition and still exhibited strong antioxidant activity after simulated gastrointestinal digestion. Taken together, SDU pretreatment could significantly increase the antioxidant activities and stability of WSPHs by improving the structure and facilitating enzymolysis of the WSP.