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To research the antioxidant activity and amino acid composition of antioxidant peptides from Macadamia integrifolia, the Macadamia integrifolia polypeptides were prepared by complex protease enzymatic hydrolysis, the constituents with optimal antioxidant activity (molecular weight less than 1000 Da) were obtained by macroporous resin and dialysis technology. The polypeptides were separated by Sephadex G-15 gel, and the scavenging and reducing ability of 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonate) radicals (ABTS+) of each component were evaluated. The optimal antioxidant components were separated and identified and analyzed by liquid chromatography and tandem mass spectrometry (LC-MS/MS). The results showed that, the G1, G2 and G3 were isolated by dextran gel column chromatography, G3 had the strongest antioxidant activity, its scavenging and reducing capacity of hydroxyl radicals was superior to glutathione with half maximal inhibitory concentration (IC50) of 6.18 mg/mL and 2.19 mg/mL, respectively. The half maximal inhibitory concentration (IC50) of scavenging capacity of DPPH and ABTS+ was 0.50 and 0.02 mg/mL, respectively. G3 was identified by liquid chromatography tandem mass spectrometry to contain 46 peptides, the length of each peptide was less than 10 amino acids. The molecular weights of the 9 peptides with matching scores more than 200 were 631~920 Da, and with no toxicity. The screened peptides with high antioxidant activity were HLLPK, KEFFP and KEFFPA, the molecular weights of them were 606.84, 666.83 and 737.92 Da, respectively. This research preliminarily revealed the antioxidant peptides composition of macadamia nut, deepened the research of antioxidant peptide of Macadamia integrifolia, and would provide a theoretical reference for the development and utilization of antioxidant peptide of Macadamia integrifolia.

Vacuum-fried products were prepared with macadamia kernels as raw material. Single factor experiment and response surface Box-Behnken test were used to optimize the vacuum frying process of macadamia kernels. Oil content, acid value, peroxidation value, color difference and sensory quality of vacuum-fried kernel were determined by comparing with raw kernel. The results showed that the effects of freezing temperature, vacuum frying temperature, vacuum frying time and vacuum degree on taste and flavor quality of macadamia kernels were significantly different (P

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