Abstract: Macadamia (Macadamia ternifolia F. Muell.) oils were obtained by spiral hot pressing, spiral cold pressing and hydraulic pressing methods. The fatty acid compositions of the oils were analyzed by gas chromatography-mass spectrometry. The color, quality indexes and total phenolic contents were determined by comparing with walnut oil as a control. The scavenging capacity against hydroxyl, superoxide anion and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonate free radicals (ABTS+·), and reducing power were investigated by comparing with walnut oil and rutin as controls. The results indicated the quality of the oil obtained by hydraulic pressing was improved compared with those obtained by other pressing methods; color parameters L, a and b values of the oil were 99.78, ?1.44 and 2.99, respectively, acid value was 0.648 6 mg/g, and peroxide value was 0.466 8 mmol/kg. The oil obtained by hydraulic pressing contained five unsaturated fatty acids, together accounting for 83.89% of the total fatty acids, including linoleic acid (62.66%), palmitoleic acid (16.75%) and octadecenoic acid (1.47%), as well as 679.11 μg/mL of total phenolics. All of the oils showed concentration dependent antioxidant activity, which could strongly scavenge hydroxyl and superoxide anion free radicals and also exhibited scavenging activity against ABTS+· as well as reducing power. The hydroxyl free radical (half maximal inhibitory concentration (IC50) = 1.31 mg/mL) scavenging activity and reducing power (IC50 = 14.78 mg/mL) of the oil obtained by hydraulic pressing were stronger than those of other oils but weaker than rutin. In addition, the superoxide anion radical scavenging activity (IC50 = 0.029 mg/mL) was higher than that of cold-pressed oil and rutin but lower than that of hotpressed oil and walnut oil at the same concentration, whereas the opposite was observed for ABTS+· scavenging activity (IC50 = 12.88 mg/mL). Correlation analysis showed that total phenolic contents in macadamia oils obtained by different pressing methods and walnut oil had good correlations with their hydroxyl and ABTS+· scavenging capacity and reducing power with R values of 0.951 9, 0.910 7 and 0.939 4 (P < 0.01), respectively.

Key words: different pressing methods, macadamia oils, quality analysis, antioxidant activity, correlation analysis