Oxidative stability and lipid composition of macadamia nuts grown in New Zealand

This study was undertaken to identify the parameters which might influence the stability and storage characteristics of some selected cultivars of macadamia nuts grown in New Zealand. Four cultivars of macadamia nuts (Macadamia tetraphylla) were harvested from the North Island of New Zealand during 1997. Total lipids, composition of fatty acids, tocopherols, sterols and stability of oils, were determined on the oil extracted from the fresh nuts. The total lipid content of the nuts ranged from 69 to 78%, while the stability of the oil measured by Rancimat test ranged from 3.6 to 19.8 h. Peroxide values of the fresh oil ranged from 0.56 to 3.61 meq O2/kg oil. The major fatty acids were oleic acid, palmitoleic acid and palmitic acid; oleic acid accounted for 40.6 to 59% of the total fatty acids. The polyunsaturated fatty acid (18:2+18:3) content was low, ranging from 3.0 to 4.7%. α-Tocopherol (0.8–1.1 μg/g lipids) and δ-tocopherol (3.5–4.8 μg/g lipids) were the only two tocopherols identified in the extracted oil. The major sterols identified were sitosterol (901–1354 μg/g lipids), Δ5-avenasterol (82–207 μg/g lipids), campesterol (61–112 μg/g lipids) and stigmasterol (8–19 μg/g lipids).