Reprint From CMS Yearbook 1973

Current demand for Macadamia nuts exceeds the supply by far. Macadamia tree acreage is increasing, but it takes 6-8 years for new groves to start producing, and 15 to 20 years to reach full production (1). Therefore, the probability of having surplus nuts that could be crushed for oil is extremely low in the foreseeable future. Because of their high oil content, Macadamia nuts are both very filling and very high in calories. The extraction of a portion of their oil by the method earlier described by Yermanos (2) would provide an additional return from nuts; at the same time, it might increase their consumption by making them more digestible, less filling and less oily, without changing their volume, appearance, or flavor. Macadamia oil could be used for cooking as well as for other purposes, especially in the cosmetics industry. A study was conducted to test this nondestructive method of extraction on Macadamia nut, and the results are presented in this report.

Oil was extracted from intact kernels of the variety Burdick from the Warren and Vacari grove (Rancho Macadamia). The kernels were immersed in one of 4 lipid solvents tested (petroleum ether, chloroform, hexane, or benzene). Whole or half nuts were placed in a 4-dram vial filled with one of these 4 solvents, capped and left at room temperature for 48 hours. Oil was recovered from the solvent following evaporation. The difference in dry weight of kernels before and after immersion represented the amount of oil extracted.

The amount of oil extracted following immersion of kernels in petroleum ether was equal to 6% of the original weight of the intact over-dried kernels. This amount rose to 14% when half kernels were used. Following drying of the extracted nuts in a vented oven at 55 C for 24 hours, the odor and taste of the solvent had disappeared completely and, if anything, the flavor of the nuts had improved. Higher amounts of oil were extracted from whole and half nuts with benzene (11.4 and 17.7%, respectively) and with chloroform (22.8 and 28.3%), but removal of such solvent odors from the nuts required prolonged drying. Similar results were obtained with other Macadamia varieties including the variety Elimbah.

In all cases the oil was colorless, transparent, and "non-greasy". Applied on the skin, it appears to be readily absorbed and has outstanding conditioning and moisturizing effects, which would make it a valuable raw material in the preparation of skin lotions, cream and bath oils.

The stability of the oil was measured with the active oxygen method for determining fat stability (AOCS Tentative Method c.d. 12-57). The oil was heated at 91.8 C for 150 hours. While one liter of dry air per minute was aspirated through a 20-gram oil sample, at the end of 150 hours, the peroxide value was about 75 M.E., per 1000 grams of oil, indicating au exceptionally high index of resistance to rancidity. By comparison, the peroxide values of cottonseed oil and corn oil exceed 95 M.E., per 1000 grams of oil at the end of 30 hours.

In view of the recent upward trends in food prices, it would seem desirable to investigate the possibility of applying the above-described technique to large-scale commercial extraction of Macadamia oil.