Macadamia nut kernels (Macadamia integrifolia, M. tetraphylla) are very high in oil, accounting for about three-quarters of their weight (Saleeb et al., 1973). The oil itself consists of ≈77% to 80% monounsaturated fat, 1% to 7% polyunsaturated fat, and the remaining 14% to 21% saturated fat (Aquino-Bolaños et al., 2017; Beuchat and Worthington, 1978; Carrillo et al., 2017; Cavaletto et al., 1966; Saleeb et al., 1973). Although unsaturated fats are considered “good” for cardiovascular health, there is a general consensus that saturated fats are detrimental (Clifton and Keogh, 2017; Sacks et al., 2017; Wang and Hu, 2017). And although the majority of fats in macadamia are “good,” the level of saturated fat present (>8 g/100 g kernels) does restrict label health claims both in Australia (Front-of-Pack Labelling Secretariat, 2018) and in the United States (Food and Drug Administration, 2003, 2017). Fatty acid profiles vary widely between nut species (Ros and Mataix, 2006) and may range widely within a species (Aquino-Bolaños et al., 2017; Mereles et al., 2017). Variation of fatty acid profiles is largely genetically based (Rodríquez et al., 2015), and is influenced primarily by the presence and activity of enzymes regulating fatty acid synthesis, elongation, and desaturation during biosynthesis (Barker et al., 2007; Brown et al., 2009). The endpoint of synthesis is usually the saturated fatty acids palmitate (C16:0) and stearate (C18:0), with the latter predominating (Harwood, 2018). Once produced, they can be subject to further elongation and desaturation. Examples of desaturation in macadamia include palmitic acid (C16:0) to palmitoleic acid (C16:1), and stearic acid (C18:0) to oleic acid (C18:1), whereas an example of elongation includes palmitic acid (C16:0) to stearic acid (C18:0).
The following investigation explores the variability in fatty acid profiles of a range of commercial cultivars and accessions in the Australian macadamia nut breeding program. The aim of this analysis was to identify the existence of reduced-saturated fat varieties, or accessions that may have potential as prospective parents for breeding a low- or a reduced-saturated fat variety. Because saturated fatty acids are the precursors of mono- and polyunsaturated fatty acids, accessions with greater unsaturated-to-saturated fatty acid ratios may further serve as a useful starting point for producing a variety with both reduced saturated fat and greater unsaturated fat.
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