Abstract：【Objective】Fatty acids are one of the main trait indicators to evaluate the fruit quality of macadamia germplasm resources, and also essential nutrients for human health. With the consumers becoming more concerned with healthy foods, large amounts of nutrition-related data are needed to screen excellent nut germplasms. Yunnan is the main producing area of macadamia nuts. This study aims to investigate the differences in fatty acid composition among seven main varieties in Yunnan and screen macadamia nut varieties rich in specific fatty acids.【Methods】Seven macadamia varieties (A16, 816, Guang 11, HAES344, HAES660, Guire 1 and Changning 1) from the macadamia planting base of the Institute of Tropical and Subtropical Cash Crops, Yunnan Academy of Agricultural Sciences (located in Baoshan city, Yunnan province) were selected as the test materials. Sample collection was carried out by using diagonal method, and 10 plants with the same vigorous and no pests and diseases were randomly selected at the maturity stage. A total of 60 macadamia nuts were collected at the low, medium, high, inside, and outside positions of canopy, and randomly divided into three groups with 20 fruit in each group. The fresh green peel was shelled, the kernel was immediately frozen and ground with liquid nitrogen, and then stored at -80 ℃ for later use. The composition and content of fatty acids in the unit fresh weight kernel were detected by liquid chromatography-mass spectrometry (LC-MS) with 50 fatty acid standards and five stable isotope labeled standards, and one-way analysis of variance (ANOVA), principal component analysis (PCA), and partial least squares discriminant analysis (PLS-DA) were used for comprehensive analysis and evaluation. 【Results】 A total of 41 fatty acids were detected in the kernels of seven macadamia varieties in Yunnan, including 13 saturated fatty acids (SFA), 18 monounsaturated fatty acids (MUFAs), and 10 polyunsaturated fatty acids (PUFAs). In terms of fatty acid content, the SFA content of the seven varieties ranged from 43726.20 to 102759.74 ng·g-1, the MUFA content from 53590.74 to 343559.73 ng·g-1, and the PUFA content from 8733.66 to 53692.72 ng·g-1. Among them, Guang 11 had the highest content of SFA, MUFA, and PUFA, followed by HAES660, and Guire 1 had the lowest values. A further analysis of the contents of various fatty acids in different varieties of macadamia nuts showed that hexadecanoic acid, palmitoleic acid, octadecanoic acid, oleic acid, cis-vaccenic acid, and linoleic acid were the main components of 41 fatty acids, among which hexadecanoic acid content ranged from 20218.83 to 56261.30 ng·g-1, palmitoleic acid content from 10360.40 to 125929.28 ng·g-1, octadecanoic acid content from 13438.66 to 42448.98 ng·g-1, oleic acid content from 18969.29 to 96976.32 ng·g-1, cis-vaccenic acid content from 18741.46 to 95181.99 ng·g-1, and linoleic acid content from 7435.72 to 51326.26 ng·g-1. The contents of hexadecanoic acid, palmitoleic acid, oleic acid, cis-vaccenic acid and linoleic acid were the highest in Guang 11; the content of octadecanoic acid was the highest in HAES660, and the contents of hexadecanoic acid, palmitoleic acid, oleic acid, cis-vaccenic acid and linoleic acid in HAES660 were second following Guang 11, which were 42381.88, 46840.31, 52791.16, 52310.95, and 19096.30 ng·g-1, respectively. The α-linolenic acid of Guang 11 and HAES660 was significantly higher than that of other varieties, which was 1619.06 and 1777.21 ng·g-1, respectively. Eicosapentaenoic acid (EPA) was highly correlated with human health, and the highest content was found in Guire 1, followed by HAES344, which was 6.26 and 4.77 ng·g-1, respectively. PCA analysis showed that the first principal component PC1 and the second principal component PC2 contained 55.5% and 18.5% of the original information, respectively, and Guang 11 and HAES660 were clearly separated from other varieties. A total of 16 characteristic fatty acids were screened by PLS-DA analysis using VIP＞1 as the screening criterion. including decanoic acid, octadecanoic acid, tridecanoic acid, dodecanoic acid, pentadecanoic acid, myristelaidic acid, petroselaidic acid, trans-10-heptadecenoic acid, trans-10-pentadecenoic acid, cis-4,7,10,13,16,19-docosahexaenoic acid (DHA), cis-5,8,11,14,17-eicosapentaenoic acid (EPA), linoelaidic acid, cis-13,16-docosadienoic acid, cis-11,14,17-eicosatrienoic acid, arachidonic acid, and γ-linolenic acid. Three characteristic fatty acids were screened by VIP ＞ 1.5, which were decanoic acid, arachidonic acid, and DHA, and the contents of decanoic acid and DHA in cultivar 816 were the highest, which were 54.63 and 120.79 ng·g-1, respectively. Guire 1 had the highest content of arachidonic acid (148.76 ng·g-1). 【Conclusion】 A total of 41 fatty acids were detected in all seven macadamia varieties in Yunnan, with Guang 11 having the highest content of fatty acids, followed by HAES660. Guang 11 had the highest contents of hexadecanoic acid, palmitoleic acid, oleic acid, cis-vaccenic acid, and linoleic acid; HAES660 exhibited the highest content of octadecanoic acid and α-linolenic acid; 816 had the highest content of decanoic acid and DHA; and Guire 1 displayed the highest content of arachidonic acid and EPA.
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