OIL CHARACTERISTICS AND OIL PRODUCTION
IN THE MACADAMIA
 
Winston W. ]ones,1. Department of Horticulture, University of California Citrus Experiment Station, Riverside, Calif.
At maturity the maeadamia nut contains from 70 to 75 per cent oil. This oil is largely the glyeeride of oleic acid with small
amounts of the glycerides of palmitic, stearic, and myristic acids. It has a saponification value of 197.3, an acid value of 0.57,
and an iodine number of 75.2. The oil is colorless and has a very bland taste.
From flowering to maturity of the nut requires approximately 215 days. Table 1 shows the changes in size of the nut during this period.
TABLE 1

Changes in the Macadamia fruit during development.

Time after
Fresh weight
Dry weight
Per cent
Condition
flowering
per embryo
per embryo
dry weight
of shell
days
grams
grams
90
1.14
0.07
6.1
soft and white
111
2.81
0.49
17.4
hard and white
136
3.41
0.99
29.0
hard and light brown
185
2.88
1.38
47.9
hard and brown
215
2.78
1.88
67.6
hard and dark brown
 
At the 90-day period the embryo (kernel) of the fruit is very small and is made up largely of water. Thereafter, there is a rapid increase in dry
weight. At 215 days (maturity) the dry weight has reached a maximum and consists largely of oil. Also, the composition of the kernel is
changing rapidly from the period of 90 to 215 days after flowering.
 
TABLE 2
Carbohydrate, nitrogen, and oil changes in the maeadamia embryo tn relation

to age. Expressed as percentage of dry weight.

 

Days After Flowering

Constituent 90 111 136 185 215
Reducing sugar 1.47 3.21 1.07 0.41 0.30
Sucrose 6.07 24.07 21.91 9./9 5.50
Total sugar 7.54 27.28 22.98 9.60 5.80
Soluble nitrogen 2.92 1.13 0.61 0.33 0.27
Insoluble nitrogen 1.96 1.91 1.58 1.39 1.43
Total nitrogen 4.88 3.04 2.19 1.72 1.70
Oil 3.46 31.19 47.94 67.28 73.44

 

  During the first 90 days after flowering there is very little oil formed in the kernel. Sugar builds up to a high level and then is converted to oil.
At muturity all constituents are at a low level except oil. Oil is at its maximum. There are marked changes in the oil during the development
of the kernel.
TABLE 3

Changes in macadamia oil in relation to age of kernel.

Days After Flowering

Oil Characteristic 90 111 136 185 215
Acid number   163.9 6.6  2.3 0.7 0.6
Saponification number 380.6 204.2 199.7 197.7 I97.3
Soluble acids (per cent) 23.7 1.7 0.5 0.2 0.2
Insoluble acids (per-cent) 48.1 81.5 86.4 94.1 94.2
Iodine number 64.4 75.4 74.4 75.7 75.2

    In the young kernel the oil consists largely of short-chain, saturated, free fatty acids. As the nut matures these are changed to the glycerides
of long-chain, unsaturated, fatty acids.

The devolopment of the Macadamia fruit is characterized by two distinct periods; the first is from flowering to the end of 90 days, during which
very little oil is formed and there is little growth of the embryo; the second period is from 90 days to maturity, a period of about 125 days
in Hawaii, during which oil is formed and the ma}or expansion of the embryo occurs. These time intervals may be somewhat different in California.

I This report is based on work done while the author was a member of the staff of the Hawaii Agricultural Experiment Station, and has been
published in Plant Physiology, Volumes 14, 1939, and 18, 1943.