Abstract: The contents of total phenols, total flavonoids and polysaccharides and the in vitro antioxidant activities of petroleum ether (PE), chloroform (CE), ethyl acetate (EAE), n-butanol (NBE) and water soluble extracts obtained from successive fractionation of the 80% ethanol extract (EE) of macadamia green husk were evaluated and the correlation between the bioactive components and the antioxidant activities was analyzed. The results showed that the contents of total phenols and flavonoids in EAE were the highest among all samples, (40.36 ± 0.48)% and (41.68 ± 0.93)%, respectively, and the content of polysaccharides in NBE was the highest, (22.08 ± 2.09)%. EE and fractions thereof all had strong scavenging capacity against 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radicals and reducing power, and also had certain scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion radicals. EAE had?the strongest scavenging capacity against DPPH and ABTS cation radicals and the highest reducing power with half maximal inhibitory concentration (IC50) of 0.67, 0.05 and 0.09 mg/mL, respectively. NBE had the strongest scavenging capacity against superoxide anion radicals with IC50 of 0.08 mg/mL, which was better than rutin at the same concentration. Pearson correlation analysis showed that for all samples, the scavenging effect on DPPH and ABTS cation radicals and reducing power were significantly positively correlated with the contents of total phenols, flavonoids and polysaccharides (P < 0.01), and the scavenging effect on superoxide anion radicals was significantly positively correlated with the content of polysaccharides (P < 0.01). The linear regression equations?between antioxidant properties and the contents of total phenols (X1), flavonoids (X2), polysaccharides (X3) and Saponins and other components (X4) were established as follows: Y1 = 7.634 4 ? 0.071 0X1 + 0.170 2X2 + 0.227 6X3 ? 0.013 3X4 for DPPH scavenging capacity, Y2 = 29.024 5 ? 0.405 0X1 + 0.320 0X2 + 0.597 2X3 for superoxide anion radical scavenging capacity, Y3 = 40.305 6 + 0.188 8X1 + 0.030 4X4 for ABTS cation radical scavenging capacity, and Y4 = 0.298 2 + 0.004 5X2 + 0.006 0X3 for reducing power, respectively. Conclusion: This study provides a certain technical basis for the development and utilization of macadamia green husk.

Key words: macadamia green husk; different polar solvents; successive fractionation; functional components; antioxidant activity; correlation