Macadamia nuts are very rich in oil. As noted previously (2) the oil has properties that have aroused interest among persons in both the vegetables cooking oil industry and the cosmetic industry. Presently, the financial returns from marketing intact kernels exceed those that might be expected from the expressed oil and residual meal. However, oil could be made available for special purposes and the kernels left intact if the nondestructive extraction method described by Yermanos and Saleeb (4) were to be used.

Macadamia oil consists of both saturated and unsaturated fractions. This paper reports on an exploratory experiment to develop a method for changing the characteristics of the oil by increasing or decreasing the unsaturated fraction to suit the purposes of the cooking oil industry and the cosmetic industry.

Materials and Methods

Nuts of the Macadamia tetraphylla variety Elimbah collected in the Nelson E. Westree planting at Carlsbad were used. When the kernels are dried to 2.5-3.0% moisture, they consist of 71% oil.

The oil was expressed in a laboratory press at 703-kg/cm² pressure. Its iodine value was determined with a Bausch and Lomb Precision Refractometer, as well as from its fatty acid composition by the following formula:

Iodine Value = 1/100 (94.6x + 85.6y + 172.4z + 81.8w)

in which x, y, z and w are the respective percentages of palmitoleic, oleic, linoleic, and eicosenoic acids.

The fatty acid composition of the oil was determined by gas liquid chromatography of methyesters prepared as described by Metcalf et al. (1). Two 6 ft. x 1/8 in. aluminum columns packed with 10% HI-EFF on 100/120 mesh Chromosorb-W, acid-washed, were used for the ester analysis, on a GC-4 Beckman chromatograph equipped with flame ionization. Column temperature was isothermal at 170 C, detector 250 C and injector 225 C; hydrogen flow was 35 ml/mm (each flame); helium 25 ml/mm (each column), and air 250 ml/min.

After the oil was extracted, it was poured into large slim test tubes and stored in a refrigerator for 4 weeks at 34 F (1.1 C). Toward the end of the third week, part of the oil changed into a solid white mass (Fig. 1). The clear portion was separated from the solidified portion, and the process was repeated until there was no further solidification.

Results and Discussion

The fatty acid compositions and the iodine values of the extracted oil, the clear remainder following prolonged refrigeration and the solidified protein are given in Table 1. In the original sample, myristic acid content was 0.6%. This is reduced to 0.35% in the solidified fraction. Palmitoleic acid was reduced from 23.6% to 17.17% oleic acid from 56.30% to 49.94%. However, arachidic acid increased from 2.70% to I 2.38%. The iodine value is reduced from 72 to 63. In the clear fraction, myristic acid was only slightly reduced from 0.60% in the extracted to 0.56% in the solid fraction, palmitoleic acid from 23.6% to 23.1 5%, and arachidic acid from 2.70% to 1.38%. Oleic acid increased from 56.30% to 59.38%. The iodine value increased from 72 to 80. The chromatographs of the liquid fraction and the solid fraction are shown in Figure 2.

This experiment shows that two kinds of oils can be separated from Macadamia oil as it comes originally from the nut by means of refrigerative fractionation, one kind high in unsaturated fatty acids, the other kind low in unsaturated fatty acids. These differences in their characteristics make them adaptable for different uses in the culinary and cosmetic trades.