Effects of thermal, microwave, and ultrasound pretreatments on antioxidative capacity of enzymatic milk protein concentrate hydrolysates

The antioxidant capacity of milk protein concentrate (MPC) subjected to hydrolysis with digestive enzymes (pepsin and trypsin) after heat (HT), microwave (MW) and ultrasound (US) pretreatments were investigated using DPPH radical scavenging and ferric reducing antioxidative power (FRAP) assays. Pretreatments were carried out for 10 min, MW and HT pretreatments at 90 °C, US at 800 W and 20 kHz. Samples were jacketed with ice during sonication while a control received no pretreatment. Compared with the control (EC50 = 0.316 mg mL−1), most pretreatments (US, US + MW, US + HT, US + MW + HT) significantly improved (P = 0.05) the radical scavenging activity and US pretreated samples showed the highest activity (EC50 = 0.283 mg mL−1) but the pretreated samples showed similar antioxidant capacity when the FRAP assay was used which could be due to the large number of peptides in the pretreated samples. US pretreatment has the potential to improve antioxidant capacity of aggregated proteins such as MPC during enzymatic hydrolysis with digestive enzymes.