Fatty acids profile of oil from nine varieties of Macadamia nut

ABSTRACT

The fatty acids profile and lipids content of the Macadamia integrifolia and Macadamia tetraphylla varieties and interspecies hybrids, M. integrifolia and M. tetraphylla were analyzed. Total lipids content ranged from 70.9 to 79.7 g of oil per 100 g⁻¹ dry-solids. Gas chromatography/mass spectrophotometry identified 20 fatty acids, the most abundant of which were oleic acid (40 to 51%), palmitoleic acid (24 to 36%), and palmitic acid (8.4 to 13.1%). Fatty acids concentration differed between varieties and hybrids (Multivariate analysis of variance, F = 13.89, p < 0.0001). A ratio of monounsaturated fatty acids:saturated fatty acid values ranged from 2.8 to 4.6. The Huatusco variety (M. integrifolia and M. tetraphylla) exhibited the highest percentage of lipids (79.7 g of oil per 100 g⁻¹ DS) and the highest monounsaturated fatty acids:saturated fatty acid (4.6), thus highlighted its potential applications within the food industry. The Cate variety (M. integrifolia and M. tetraphylla) had the lowest monounsaturated fatty acids:saturated fatty acid, suggesting potential uses in the cosmetics industry.

KEYWORDS:

• Fatty acids composition
• Lipids content
• Macadamia integrifolia
• Macadamia tetraphylla.

Introduction

Cardiovascular diseases (CVDs) are the leading cause of death around the world. In 2008, an estimated 17.3 million people died from CVDs.^[1] Risk factors for CVDs include high levels of total cholesterol (TC), triglycerides (TG), and low-density lipoproteins (LDL), in addition to low levels of high-density lipoproteins (HDL).^[2] Changes in dietary habits can help mitigate these risk factors. This is why the American Heart Association (AHA) recommends low-fat diets (Step I and Step II) to help lower plasma cholesterol levels, and substitute energy content from saturated fatty acids (SFAs) with that from carbohydrates.^[3]

Carbohydrates can efficiently reduce TC and LDL levels; however, blood TG levels can still rise and HDL levels can still drop.^[3] As an alternative to carbohydrate intake, a diet rich in monounsaturated fatty acids (MUFA) neither increases TG levels, nor does it affect HDL concentrations.^[3,4] Nuts and some dried fruits have high MUFA contents. Furthermore, in 2003, the U.S. Food and Drug Administration (FDA) established that, in addition to a diet low in saturated fats and cholesterol, the consumption of some nuts, including macadamia nuts, in portions of 42.5 g day⁻¹, could reduce the risk of developing CVDs.^[5]

The macadamia nut tree comes from the Macadamia genus, originate from eastern Australia. While there are at least five species of macadamia trees, there are only two that produce edible nuts: the Macadamia integrifolia Maiden and Betche and M. tetraphylla L.A.S. Johnson. In addition, hybrid varieties between the two species exist and are commercially important.^[6] The macadamia nut has a high lipids content (70.1 g of oil per 100 g⁻¹ in M. integrifolia^[7] and 69 to 78 g of oil per 100 g⁻¹ in M. tetraphylla),^[6] but a low percentage of SFA. Almost 80% of its fatty acids (FAs) are monounsaturated, mostly oleic (C18:1; ~60%) and palmitoleic acids (C16:1; ~20%).^[8] Other FAs identified in macadamia nuts include: lauric (C12:0), myristic (C14:0), palmitic (C16:0), stearic (C18:0), arachidic (C20:0), behenic (C22:0), lignoceric (C24:0), eicosenoic (C20:1), erucic (C22:1), linoleic (C18:2), and linolenic (C18:3) acids.^[6,8,9,10]

Its FA profile helps to improves blood lipid profiles and decreases inflammation and oxidative stress, thus contributing to lowering body mass and generally reducing CVD risk factors.^[11,12] Biological-clinical studies involving animals and humans have shown that the intake of macadamia nuts helps to lower TC and LDL levels.^[11,13–16] Most studies of the FAs profiles of macadamia nut have been carried out on nuts from M. integrifolia varieties and the functional importance of their MUFA. The aim of this study was to evaluate the FA profiles of macadamia nuts taken from a collection of M. integrifolia and M. tetraphylla varieties and interspecific hybrid varieties which are grown in Veracruz, Mexico.

Materials and methods

Orchard sample collection

The varieties of Macadamia evaluated are currently being cultivated in a commercial orchard located in Coatepec, Veracruz, Mexico (19° 28’ 47”N, 96° 59’ 28”W). In 2013, during the harvest, the orchard and its plants were divided into three sections for sample purposes. Then, a compound sample of nut kernels was taken from 3 to 10 trees per variety. Agro-ecologically, the farm sampled is located in a semi-warm/humid climate with temperatures ranging from 13.3 to 27.8°C. It is located 1530 m above sea level and has an average rainfall of between 1500 and 2200 mm.^[17] The orchard sampled contains 614 trees of nine different varieties, which were planted 10 years ago. Robledo-Martinez and Escamilla-Prado,^[18] and Robledo et al.^[19] have documented a full description of the varieties evaluated.

Once the individual plants from each variety were labeled, a sample of dehiscent nuts (20 kg) were collected from the following Macadamia varieties: (1) M. integrifolia (cv Ika Ika 333); (2) M. tetraphylla (cv Alberca-527 (A-527) and L1); and, (3) M. integrifolia x M. tetraphylla (cv Cate, Lewis, UCLA, Beaumont 695, Huatusco and Victoria). The nuts were collected during the period of September to November of 2013.

Sample preparation

The pericarp was removed mechanically and the nut or nucule dried for 24 h at 35°C, followed by 12 h at 45°C and 12 h at 60°C. A forced air dryer was used to reduce nut moisture content and facilitate the removal of shells or testa.

Oil extraction

A subsample of 500 g was ground in a blender, and the resulting paste was then placed in a hydraulic press (PowerTeam, Model A, USA) at a compressive force of 10 tons for 60 s. The oil was centrifuged at 8000 × g for 20 min (Biofuge primo R, Heraeus, USA) in order to eliminate any solid residues. The supernatant was then placed in amber flasks, after which nitrogen gas was used in order to eliminate any air, and then they were stored at –20°C until analyzed.

Total lipids content

The total lipids content was measured by means of the Soxhlet method (930.39),^[20] using petroleum ether as the extraction medium.

FA composition

FA identification and quantification was carried out using the methylation method,^[21] Fifty milligrams of oil was dissolved in 900 µL high-performance liquid chromatography (HPLC)-grade chloroform. Esterification was achieved by adding 100 µL 5 N of sodium methoxide (Sigma Aldrich) and stirring for 5 min. The FA analysis was carried out using a gas chromatograph (model 7890 A, Agilent Technologies, Inc., CA, USA) attached to a mass detector (model 5975 C, Agilent Technologies) and equipped with a split/splitless injector and a selective mass detector operating at 70 eV (electronic impact mode). The FAs were separated using a capillary column (HP-88, Agilent, 100 m × 0.250 mm × 0.20 µm) and the following temperature series: initial temperature, 50°C; increase to 85°C at 2.5°C min⁻¹; increase to 170°C at 10°C min⁻¹; constant 170°C for 20 min; final increase to 250°C at 10°C min⁻¹; and a constant 250°C for 25 min. Using a 2:1 split, 1 µL methylated sample was injected, with the injector temperature at 250°C. The carrier gas was helium at a flow rate of 4 mL min⁻¹. Identification of the individual FA was accomplished using MSD ChemStation E.02.00.493 software (Agilent Technologies, USA) and the National Institute of Standards and Technology (NIST) database. The area under each FA peak, relative to the total area of all FA peaks, was used to quantify the FAs identified. The results obtained are reported as percentage of FA according to Ayyildiz et al.^[22] All samples were analyzed in quadruplicate.

Statistical analysis

Total lipids content data was analyzed using a generalized linear model (GLM) and a one-way analysis of variance (ANOVA) in which the factor variety was included in nine levels, each one corresponding to the studied varieties. The FAs profile response variables were analyzed with a GLM and a Multivariate analysis of variance (MANOVA). After each analysis, a Tukey test (α = 0.05) was applied to compare averages for each response variable. The measurement of each response variable was carried out using independent experimental units (i.e., samples): four replicates for the FA profile and two for the total lipid content. The authors checked in order to satisfy the assumptions of normality and homogeneity of each variance. All statistical analyses was processed using STATISTICA 7.0 software (StatSoft Inc. 1984–2004).

Results and discussion

Lipids content

The average nut oil content differed between varieties of Macadamia (F = 15.64, p < 0.01). The Macadamia integrifolia variety (Ika Ika 333) had an average oil content of 76.7 g of oil per 100 g⁻¹ DS, while the M. tetraphylla varieties had contents of 75.2 g (A-527) and 79.7 g of oil per 100 g⁻¹ DS (L1). The oil content in the interspecies hybrid varieties ranged from 70.9 to 79.7 g of oil per 100 g⁻¹ DS (Table 1). The overall oil content was highest (76.7 to 79.7 g of oil per 100 g⁻¹ DS) in the Huatusco, L1, Beaumont 695 and Ika Ika 333 varieties. The lipid concentrations found were generally higher than previously reported values: 59,^[9] 76.2,^[23] 66.16,^[8] 68 to 71,^[24] and 40 to 60 g of oil per 100 g⁻¹.^[25] Lipid content values for the M. tetraphylla varieties were close to the upper limit for this species (69–78 g of oil per 100 g⁻¹).^[6] The differences observed in lipid content, compared to other studies, could be attributed to cultivation, environmental, and horticultural factors, such as rainfall, temperature, water stress, and nitrogen fertility.^[26–28] Furthermore, the lipid extraction method could also have an impact on these results. The lipid contents of Macadamia nut varieties studied are also notably higher than in other commercially important nuts: hazelnuts (61.46 g per 100 g⁻¹);^[8] pecans (64.5 g per 100 g⁻¹);^[8] pistachios (50 g per 100 g⁻¹);^[29] and almonds (53 g per 100 g⁻¹).^[29]

Table 1 Lipids content (g of oil per 100 g⁻¹ dry-solids) and fatty acids composition of oil (%) from nine varieties of Macadamia nut.

	Variety
	Ika Ika 333	A-527	L1	Cate	Lewis	UCLA	Beaumont 695	Huatusco	Victoria
Lipids content	76.7 ± 0.7^cd	75.2 ± 0.7^bc	79.7 ± 0.7^d	74.7 ± 0.7^abc	74.8 ± 0.7^abc	72.6 ± 0.7 ^ab	77.7 ± 0.7^cd	79.7 ± 0.7^d	70.9 ± 0.7^a
C10	0.005 ± 0.00^a	ND	ND	ND	ND	ND	ND	ND	0.003 ± 0.00^a
C12	0.08 ± 0.01^bc	0.177 ± 0.0^ab	0.12 ± 0.01^abc	0.11 ± 0.01^abc	0.11 ± 0.01^bc	0.09 ± 0.01^bc	0.09 ± 0.01^bc	0.06 ± 0.01^cd	0.14 ± 0.01^ab
C14	0.7 ± 0.2^b	1.6 ± 0.2^a	0.9 ± 0.2^ab	0.9 ± 0.2^ab	1.0 ± 0.2^ab	0.7 ± 0.2^b	1.0 ± 0.2^ab	0.7 ± 0.2^b	1.4 ± 0.2^ab
C16	13.1 ± 0.5^a	10.0 ± 0.5^bc	9.3 ± 0.5^c	12.2 ± 0.5^a	9.6 ± 0.5^c	11.0 ± 0.5^a	11.0 ± 0.5^a	8.4 ± 0.5^c	10.4 ± 0.5^bc
C16:1	24 ± 1^c	25 ± 1^bc	36 ± 1^a	26 ± 1^bc	26 ± 1^bc	28 ± 1^b	24 ± 1^c	26 ± 1^bc	29 ± 1^b
C16:2	ND	0.001 ± 0.00^a	ND	ND	ND	ND	ND	ND	0.001 ± 0.00^a
C17	ND	ND	ND	0.9 ± 0.3^a	ND	ND	ND	ND	ND
C18	6.1 ± 0.4^a	6.1 ± 0.4^a	4.7 ± 0.4^bc	5.5 ± 0.4^a	4.6 ± 0.4^b	5.3 ± 0.4^ab	4.4 ± 0.4^bc	4.6 ± 0.4^b	5.3 ± 0.4^ab
C18:1 Δ9 + C18:1 Δ11	45 ± 2^bc	43 ± 2^cd	40 ± 2^d	44 ± 2^cd	46 ± 2^b	45 ± 2^bc	48 ± 2^ab	51 ± 2^a	41 ± 2^cd
C18:2	1.6 ± 0.8^c	3.4 ± 0.8^a	2.1 ± 0.8^bc	2.7 ± 0.8^abc	3.7 ± 0.8^a	2.1 ± 0.8^bc	3.2 ± 0.8^ab	2.2 ± 0.8^bc	2.9 ± 0.8^a
C20	3.9 ± 0.2^ab	4.6 ± 0.2^a	3.6 ± 0.2^bc	3.8 ± 0.2^ab	3.7 ± 0.2^ab	3.9 ± 0.2^ab	3.3 ± 0.2^bc	2.9 ± 0.2^c	4.0 ± 0.2^ab
C18:3	0.22 ± 0.01^bc	0.27 ± 0.01^ab	0.18 ± 0.01^c	0.21 ± 0.01^c	0.20 ± 0.01^c	0.28 ± 0.01^ab	0.20 ± 0.01^c	0.23 ± 0.01^bc	0.30 ± 0.01^a
C20:1	3.5 ± 0.2^ab	3.7 ± 0.2^a	2.80 ± 0.15^bcd	2.3 ± 0.2^d	3.4 ± 0.2^abc	2.6 ± 0.2^cd	3.3 ± 0.2^abc	2.6 ± 0.2^cd	3.5 ± 0.2^ab
C21	0.007 ± 0.00^cd	0.030 ± 0.00^a	0.006 ± 0.00^cd	0.011 ± 0.00^bcd	0.005 ± 0.00^d	0.014 ± 0.00^bcd	0.018 ± 0.00^abc	0.006 ± 0.00^cd	0.023 ± 0.00^ab
C22	1.3 ± 0.1^ab	1.7 ± 0.1^a	0.7 ± 0.1^cd	0.9 ± 0.1^bcd	1.2 ± 0.1^abc	0.9 ± 0.1^bcd	1.2 ± 0.1^abc	0.6 ± 0.1^d	1.5 ± 0.1^a
C22:1	0.27 ± 0.03^bc	0.46 ± 0.03^a	0.14 ± 0.03^c	0.16 ± 0.03^c	0.26 ± 0.03^c	0.14 ± 0.03^c	0.31 ± 0.03^abc	0.15 ± 0.03^c	0.44 ± 0.03^ab
C23	0.011 ± 0.00^ab	0.027 ± 0.00^a	0.003 ± 0.00^b	0.010 ± 0.00^ab	0.017 ± 0.00^ab	0.014 ± 0.00^ab	0.017 ± 0.00^ab	0.007 ± 0.00^ab	0.022 ± 0.00^ab
C24	0.49 ± 0.02^a	0.54 ± 0.02^a	0.30 ± 0.02^a	0.23 ± 0.02^c	0.34 ± 0.02^b	0.27 ± 0.02^bc	0.32 ± 0.02^bc	0.27 ± 0.02^bc	0.47 ± 0.02^a
C25	ND	0.01 ± 0.00^a	ND	ND	ND	ND	ND	ND	ND
C26	0.05 ± 0.01^ab	0.06 ± 0.01^b	0.01 ± 0.01^b	0.02 ± 0.01^ab	0.03 ± 0.01^ab	0.02 ± 0.01^ab	0.04 ± 0.01^ab	0.13 ± 0.01^a	0.05 ± 0.01^ab
SFA	25.7 ± 0.9^ab	24.7 ± 0.9^bc	19.5 ± 0.9^ef	24.7 ± 0.9^bc	20.7 ± 0.9^de	22.1 ± 0.9^cde	21.5 ± 0.9^de	17.5 ± 0.9^f	23.3 ± 0.9^bcd
MUFA	72 ± 2^de	72 ± 2^e	78 ± 2^ab	72 ± 2^de	75 ± 2^bcd	76 ± 2^bc	75 ± 2^cd	80 ± 2^a	74 ± 2^cde
PUFA	1.9 ± 0.8^d	3.6 ± 0.8^a	2.3 ± 0.8^cd	2.9 ± 0.8^abcd	3.9 ± 0.8^a	2.4 ± 0.8^bcd	3.4 ± 0.8^ab	2.4 ± 0.8^bcd	3.2 ± 0.8^abc
MUFA/SFA	2.8 ± 0.2^f	2.9 ± 0.2^def	4.0 ± 0.2^ab	2.9 ± 0.2^ef	3.7 ± 0.2^bc	3.4 ± 0.2^bcdef	3.5 ± 0.2^bcde	4.6 ± 0.2^a	3.2 ± 0.2^cdef

Results are given as means (± EE).

Means in the same line followed by different letters are significantly different (p<0.05).

Individual fatty acids were calculated as the percentage of total fatty acids.

SFA: saturated fatty acids, MUFA: monounsaturated fatty acids, PUFA: polyunsaturated fatty acids, ND: not detected.

FA Profile

FA concentrations differed between varieties (MANOVA, F = 13.89, p < 0.0001). Total SFA levels in the varieties studied varied between 17.5 and 25.7%, with differences (F = 23.49, p < 0.0001) between them. In M. integrifolia (var. Ika Ika 333), total SFA was 25.7% higher than the 12.06 to 16.77% reported previously.^[12,25] M. tetraphylla (variety A-527) had a total SFA of 24.7%, and variety L1 had an SFA level of 19.5%. Both of these are higher than the 13.2 to 17.8% reported for other varieties of the same species.^[6]

Individual FA levels also differed between the varieties studied: lauric (F = 4.98, p < 0.0001); myristic (F = 4.73, p < 0.0001); palmitic (F = 16.03, p < 0.0001); stearic (F = 9.42, p < 0.0001); arachidic (F = 6.31, p < 0.0001); heneicosanoic (F = 8.73, p < 0.0001); behenic (F = 27.50, p < 0.0001); tricosanoic (F = 4.00, p < 0.0001); lignoceric (F = 13.20, p < 0.0001); pentacosanoic (F = 960.0, p < 0.0001); and cerotic (F = 5.79, p < 0.0001). The SFA with the highest abundance was palmitic acid, particularly in the Ika Ika 333 variety (Table 1). By using the mass detector, we were able to identify FAs that were rarely reported, including the occurrence of straight-chain, odd-numbered FAs, such as heptadecenoic (C17), heneicosanoic (C21), and pentacosanoic acid (C25), although in low concentrations (Table 1).

Most of the FAs in the studied macadamia nut varieties studied were MUFAs, with values ranging from 72 to 80% and differences between varieties (F = 17.65, p < 0.0001). The Huatusco variety had the overall highest MUFA concentration (Table 1). Concentrations of individual MUFA’s also differed among varieties: palmitoleic (F = 9.57, p < 0.0001); oleic (F = 12.06, p < 0.0001); eicosenoic (F = 9.15, p < 0.0001); and erucic (F = 10.29, p < 0.0001). Oleic acid (ω-9) was the most abundant MUFA. Its inclusion in the human diet helps to reduce the risk of CVD, arrhythmia, and strokes, in addition to lowering LDL cholesterol levels and increasing the concentration of HDL.^[30,31] Furthermore, it helps to lower blood pressure, decreases the risk of thrombosis and increases arterial vasodilation.^[32] The Huatusco and Beaumont varieties have the highest concentrations of this acid: 51 and 48%, respectively. Macadamia integrifolia (var. Ika Ika 333) has lower oleic acid levels than the 58.35% reported by Venkatachalam and Sathe^[8] and the 65.5% reported by Maguire et al.,^[9] but higher than the 43.7% reported for the same species by Wood and Garg.^[12] In the two M. tetraphylla varieties (A-527 and L1), oleic acid levels were within the 40.5 to 54.4% reported by Kaijser et al.^[6] Palmitoloeic acid had the second highest concentrations of all MUFAs; M. tetraphylla (var. L1) recorded the highest levels of this MUFA (Table 1).

The range for PUFA values was between 1.9 and 3.9%, with contrasts between the varieties (F = 19.03 p < 0.0001; Table 1). The varieties with the highest content were A-527 and Lewis. Ika Ika 333 contained Polyunsaturated fatty acids (PUFA) levels similar to those reported by Wood and Garg (1.5%),^[12] but lower than those reported by Venkatachalam and Sathe^[8] for M. integrifolia (4.39%). Both A-527 and L1 recorded levels close to the lower limit for M. tetraphylla.^[6] The hybrids (M. integrifolia × M. tetraphylla) had concentrations between 2.3 and 3.9%, which are close to the values reported for both species. Varieties also differed in terms of individual PUFA levels: Victoria, UCLA, and A-527 had the highest levels of linolenic acid (ω-3) content (0.27–0.30%). ω-3 FAs are vitally important components in ensuring the normal growth of brain tissue and the retina. The consumption of these acids is associated with improved memory and learning capacity.^[33,34] A-527, Lewis, Beaumont 695, Victoria, and Cate varieties had the highest levels of linoleic acid (ω-6), which is an essential FA in metabolizing polyunsaturated fatty acids. It is necessary in subcutaneous fats, and its consumption is associated with a decreased risk of coronary heart disease.^[31,35] Traces of 9,12-hexadecadienoic acid were detected in A-527 and Victoria. The difference between the concentration of individual FAs in this study compared to others could be a result of genetic, environmental, and horticultural factors, the extraction and derivatization methods used, and the analysis conditions (column and detector), as outlined by Venkatachalam and Sathe.^[8]

Food containing low levels of SFAs is generally accepted as having a positive impact on the health of human beings, given that the consumption of SFAs is known to increase blood TC and LDL-cholesterol concentrations.^[36] On the other hand, the consumption of MUFAs has a positive impact on health by lowering LDL levels and raising HDL levels, reducing arterial pressure, increasing arterial vasodilation, and improving glucose metabolism in people with diabetes.^[12,14] The PUFAs are even more efficient at lowering LDL, but they also reduce HDL levels.^[36]

Diets rich in MUFAs and low in SFAs can, therefore, effectively lower blood cholesterol and LDL concentrations.^[37] In the Macadamia varieties studied, the MUFA/SFA ratio was heterogeneous (F = 25.43, p < 0.0001, Table 1), with the Huatusco variety having the highest value (4.6) and the Ika Ika 333 variety the lowest (2.8). The MUFA/SFA ratios of the nine studied varieties are slightly lower than the 4.93 reported for M. integrifolia;^[12] however, they are higher than the ratios reported for other tree nuts such as the Brazil nut (Bertholetia excelssa, 1.14); cashews (Anacardium occidentale, 2.92); pine nuts (Pinus pinea, 1.14); pistachios (Pistachia vera, 3.61); and pecans (Juglans regia, 1.29).^[8]

The relationship between the total lipids content and the MUFA/SFA ratio shows that the Huatusco variety has the highest overall lipids content as well as the highest ratio values (Fig. 1). This identifies it as a promising candidate for greater production and consumption. The Ika Ika 333 variety, on the other hand, has the lowest ratio value but the highest concentration of of SFA’s, such as palmitic and stearic acids, which play a leading role in cell membrane renewal and the mechanical functions of permeability.^[38,39] In conjunction with its high percentage of lipids, this suggests it should be used in the manufacturing of skin and hair care products.

Figure 1. Lipids content (grams of oil per 100 g⁻¹ of dry-solids) versus MUFA/SFA ratio of oil from nine varieties of Macadamia nut.

Conclusion

Due to their relatively high oil content, nuts from the hybrid Huatusco and Beaumont 695, M. tetraphylla var. L1, and M. integrifolia var. Ika Ika 333 varieties are promising options for oil extraction. Oil from the Huatusco variety had the highest MUFA/SFA ratio, suggesting that it could effectively lower blood TC and LDL levels, as well as having possible uses as a functional food or food ingredient. The FAs profile of oil from the Ika Ika 333 variety contained a higher percentage of SFAs, suggesting possible applications in hair and skin care products.

Funding

This work was supported by Fundación Educación Superior-Empresa, A.C. LMV received a scholarship from the CONACyT (No. 279502) to study a Master’s in Food Sciences. Biological material was provided by the Unión de Productores Agropecuarios y Forestales de la Zona Alta de Coatepec, Veracruz, A.C.

Additional information

Funding

This work was supported by Fundación Educación Superior-Empresa, A.C. LMV received a scholarship from the CONACyT (No. 279502) to study a Master’s in Food Sciences. Biological material was provided by the Unión de Productores Agropecuarios y Forestales de la Zona Alta de Coatepec, Veracruz, A.C.