Preparation Technology and Antioxidant Activities of Different Molecular Weight Macadamia Nut Polypeptides

Macadamia nut polypeptides were prepared by enzymatic hydrolysis of macadamia nut meal, and suitable proteases for the preparation of macadamia antioxidant polypeptides were screened with ABTS⁺ radical scavenging effects as evaluation indicators. Four constituents (MNAP-1, MNAP-2, MNAP-3, MNAP-4) were obtained by DA201-C macroporous resin and dialysis technology. The scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·), hydroxyl radical and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonate radicals) radical (ABTS⁺·), and reducing power were investigated by comparing with glutathione as controls. The results showed that the suitable protease was complex protease for the preparation of macadamia antioxidant polypeptides, which was better than neutral protease, acid protease, alkaline protease, papain and bromelain at the same concentration. Antioxidant activities of different molecular weight macadamia nut polypeptides were different, which all had strong scavenging capacity against DPPH and ABTS⁺ radicals, and also had certain scavenging capacity against hydroxyl radical and reducing power. MNAP-4 (molecular weight less than 1000 Da) had the strongest scavenging capacity against DPPH, ABTS⁺ and hydroxyl radicals and the highest reducing power with half maximal inhibitory concentration (IC₅₀) of 0.36, 6.75, 0.08 and 3.19 mg/mL, respectively, which was lower than other molecular weight polypeptides. Correlation analysis showed different molecular weight macadamia nut polypeptides had good correlations with their DPPH, hydroxyl and ABTS⁺ radicals scavenging capacity and reducing power with r values of 0.947, 0.964, 0.948 and 0.856 (P<0.01), respectively. The complex protease hydrolysates from macadamia nut meal contained good antioxidant activity polypeptides, which could provide a theoretical basis for the preparation and application of antioxidant peptides.