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Article

Dynamic Changes in Fatty Acids in Macadamia Fruit During Growth and Development

by
Mingqun Cao
1,2,†,
Birong Zhang
1,†,
Minxian Duan
1,
Hanyao Zhang
2,
Suyun Yan
1,
Fan Yang
1,
Wenbin Shi
1,
Xiaomeng Fu
1,
Hongxia Yang
1,
Jinxue Li
3,* and
Xianyan Zhou
1,*
1
National Key Laboratory of Tropical Crop Biological Breeding, Institute of Tropical and Subtropical Cash Crops, Yunnan Academy of Agricultural Sciences, Baoshan 678000, China
2
Yunnan Provincial Key Laboratory for Conservation and Utilization of In-Forest Resource, Southwest Forestry University, Kunming 650224, China
3
School of Biotechnology and Engineering, West Yunnan University, Lincang 675800, China
*
Authors to whom correspondence should be addressed.
†
These authors have contributed equally to this work.
Agronomy 2025, 15(7), 1682; https://doi.org/10.3390/agronomy15071682
Submission received: 6 June 2025 / Revised: 27 June 2025 / Accepted: 10 July 2025 / Published: 11 July 2025
(This article belongs to the Section Plant-Crop Biology and Biochemistry)
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Abstract

Fatty acids tend to undergo dynamic changes during the growth and development of fruits. In this study, we analyzed the variations in fruit morphology and kernel fatty acid fractions and contents at seven post-flowering stages in the fruit of ‘A4’ and ‘OC’, two main macadamia cultivars in Yunnan, China. The single fruit weight and longitudinal and transverse diameters showed a ‘fast–slow–stable’ growth trend, and the fruit shape index gradually decreased with fruit development. A total of 13 saturated fatty acids, 18 monounsaturated fatty acids, and 10 polyunsaturated fatty acids were detected in macadamia kernels at seven developmental stages. The total fatty acid content in ‘OC’ and ‘A4’ tended to first increase and then decrease. The fatty acid content accounted for 8.81% and 6.33% of the total fatty acids at 50 days after flowering (DAF), and peaked at 95 DAF and 125 DAF (the fatty acid content accounted for 25.61% and 20.69% of the total fatty acids), indicating that these two periods are critical for fatty acid accumulation in the two cultivars. In addition, oleic acid, palmitoleic acid, cis-Vaccenic acid, and hexadecenoic acid were determined as the main fatty acids. This study reveals the dynamic changes in fatty acid composition and content in ‘OC’ and ‘A4’ during fruit development, providing a scientific basis for determining the appropriate harvesting time for macadamia nuts.

1. Introduction

The Macadamia genus belongs to the Proteaceae family and originates from Australia. It is an evergreen fruit tree with a tree height of 5–15 m [1]. The planting area of macadamia has reached 581,100 ha across the world, and is about 359,400 ha in China, which accounts for approximately 62% of the global planting area [2]. In China, macadamia is mainly planted in Yunnan, Guangxi, Guangdong, Guizhou, and some other hot zones [3]. Particularly in Yunnan, China, the planting area reaches 276,000 ha, accounting for approximately 50% of the global and 82% of China’s planting area. China’s total production of macadamia nuts (shell nuts) is about 109,000 tons, and about 90,000 tons of macadamia nuts are imported every year, while only about 4100 tons of macadamia nuts are exported. Hence, about 50% of macadamia nut consumption in China is still dependent on imports. Macadamia nuts are crispy, smooth, and delicious with a unique creamy flavor, making them stand out among many other nuts. Macadamia nuts have high contents of amino acids (76.29 g kg−1), phenolic acids (471.7 mg kg−1), and vitamins (39.8 mg kg−1) [4]. In addition, their unique fatty acid composition contributes to their high nutritional value, and their unsaturated fatty acid content is particularly high, accounting for 82.73–82.75% of the kernel mass [5]. Fatty acids are the main components of neutral fats, phospholipids, and glycolipids. According to their chemical structure, fatty acids can be divided into saturated fatty acids (SAFs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs). MUFAs, such as oleic acid, have been shown to help lower low-density lipoprotein (LDL) levels in the blood, thereby reducing the risk of heart disease and stroke [6]. PUFAs, such as linoleic acid and α-linolenic acid, are essential to human health because the human body cannot synthesize them independently and they must be ingested through the diet [7]. PUFAs are known to prevent cardiac arrhythmias, regulate vascular endothelial cell function, improve vasorelaxation, and reduce platelet aggregation and arterial inflammatory responses [8,9,10,11,12]. These fatty acids are crucial in maintaining cardiovascular health, promoting brain development, regulating inflammatory responses, and preventing chronic diseases.
There are numerous reports that the content of various fatty acids changes during fruit development. Bouali et al. [13] reported that the total lipid content gradually increases during walnut development; however, the SFA and PUFA contents gradually decline after maturity, while the content of MUFAs gradually increases. Rezanejad & Shekari [14] studied the fatty acids in two pistachio varieties at different stages of growth and development, and reported that the total fatty acid content decreased along with fruit ripening; however, the content of MUFAs increased, and the content of oleic acid, a dominant MUFA, first increased and then gradually decreased after reaching the peak. Koaze et al. [15] investigated the physiological characteristics of macadamia nuts at four developmental stages. They found that the total fatty acid content increased significantly along with fruit development, whereas the water content significantly decreased five months after flowering, and the contents of stearic acid and oleic acid gradually increased with further fruit growth.
Several studies have investigated the fatty acid profile of commercial macadamia cultivars to provide a basis for the identification of primary fatty acids [16]. Oleic acid and palmitoleic acid were identified as the dominant MUFAs in macadamia nuts [5]. The primary fatty acids are the MUFAs oleic acid and palmitoleic acid, whose contents are generally 57–67% and 14–24%, respectively, followed by the SFA palmitic acid (0.7–10%), while the remaining PUFAs (linolenic acid and α-linolenic acid) together account for less than 2% of the total [17]. Anna Kaijser et al. [18] found that the major fatty acids in macadamia nuts grown in New Zealand were oleic, palmitoleic, and palmitic acids, with oleic acid accounting for 40–59% of the total fatty acids, and the unsaturated fatty acid content being as low as 3–5%. In terms of research content, most current studies focus on conventional areas such as macadamia nut varietal breeding, cultivation techniques, pest and disease management, and nutritional components. In contrast, this study delves into the dynamic changes in fatty acid composition and content during the development period of macadamia nuts, involving more detailed aspects. Regarding research methods, this study employs metabolomics analysis technology to comprehensively assess the influence of different developmental stages on fatty acid accumulation, providing more forward-looking and precise theoretical support for the global nut industry development.
Regarding cultivar selection, ‘OC’ (early-maturing) and ‘A4’ (mid-maturing) [19] are the main macadamia varieties cultivated in Yunnan. In agricultural practice, fatty acid content is closely related to the maturity period of the varieties. Understanding these contents is essential for rationally scheduling harvest time. Therefore, elucidating the variations in fatty acid content during different developmental stages of macadamia has significant implications for cultivar selection and agricultural practices. This study aims to reveal the patterns of fatty acid composition and accumulation in ‘OC’ and ‘A4’ at various growth stages, providing a scientific basis for determining the optimal harvest time.

2. Materials and Methods

2.1. Materials and Reagents

2.1.1. Test Materials

This study investigates the developmental changes in kernel fatty acids in two major macadamia (Macadamia integrifolia) cultivars, ‘A4’ and ‘OC’, cultivated in Yunnan, to determine the optimal harvesting window.
‘A4’ and ‘OC’ trees were obtained from the macadamia planting base of the Institute of Tropical and Subtropical Economic Crops, Yunnan Academy of Agricultural Sciences, located in Baoshan City, Yunnan Province, China (25°4′ N, 99°11′ E, 799 m above sea level), with a soil pH of 4.90, indicating acidic conditions. The sampling period spanned from 23 May to 21 August 2024, with specific samplings conducted at 50 (23 May), 65 (7 June), 80 (22 June), 95 (7 July), 110 (22 July), 125 (8 August), and 140 (21 August) DAF (DAF: days after flowering). Within the experimental area, a total of 9 trees were selected for tagging and divided into 3 biological replicates (each replicate containing 3 trees). Ten nuts were collected from the lower, middle, and upper layers of the canopy of each replicate, for a total of 30 nuts collected for photography and sampling.

2.1.2. Reagents and Instruments

Ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) was used (ExionLC™ AD UHPLC-QTRAP® 6500+, AB SCIEX Corp., Boston, MA, USA) to detect the metabolites in the fruit.
All 50 fatty acid standards and five stable isotope-labeled standards were obtained from ZZ Standards Co., Ltd. (Shanghai, China). Isopropanol (Optima LC-MS), acetonitrile (Optima LC-MS), and formic acid (Optima LC-MS) were purchased from Thermo-Fisher Scientific (Fairlawn, NJ, USA). Ultrapure water was purchased from Merck Millipore (Billerica, MA, USA).

2.2. Experimental Methods

2.2.1. Determination of Single Fruit Weight and Longitudinal and Transverse Diameter of Fruits

The green-skinned and shelled fruits were weighed individually using an electronic balance (accuracy 0.001 g). The longitudinal and transverse diameters of the green-skinned fruit and shelled fruit were measured with Vernier calipers to calculate the fruit shape index of the green-skinned fruit and shelled fruit, and the fruit shape index = longitudinal diameter/transverse diameter.

2.2.2. Standard Solution Preparation

The stock solutions of individual fatty acids were mixed and prepared in a fatty-acid-free matrix to obtain a series of fatty acid calibrators at concentrations of 40,000, 20,000, 10,000, 4000, 2000, 1000, 400, 200, 100, 40, 20, and 10 ng/mL. Expected concentrations of 2, 4, 8, 20, 40, 80, 200, 400, 800, 2000, 4000, and 8000 ng/mL of decanoic acid-d19, myristic acid-d2, octadecanoic acid-d35, eicosanoic acid-d39, and lignoceric acid-d4 were compounded and mixed as internal standards (ISs). The stock solutions and working solutions were stored in a refrigerator at −20 °C.

2.2.3. Metabolite Extraction

A diluted sample of 100 μL was taken by adding 100 mg of kernel to 1 mL of water. Then, 100 μL of each mixture was homogenized with 300 μL of isopropanol/acetonitrile (1:1), which contained mixed internal standards, and centrifuged at 12,000 rpm for 10 min. Finally, the supernatant was injected into the LC-MS/MS system for analysis, with three repeats.

2.2.4. LC-MS Analysis

An ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) system (ExionLC™ AD UHPLC-QTRAP 6500+, AB SCIEX Corp., Boston, MA, USA) was used to quantitate fatty acids by Novogene Co., Ltd. (Beijing, China). Separation was performed on a Waters ACQUITY UPLC BEH C18 column (2.1 × 100 mm, 1.7 μm) which was maintained at 50 °C. The mobile phase, consisting of 0.05% formic acid in water (solvent A) and isopropanol/acetonitrile (1:1) (solvent B), was delivered at a flow rate of 0.30 mL/min. The solvent gradient was set as follows: initial 30% B, 1 min; 30–65% B, 2 min; 65–100% B, 11 min; 100% B, 13.5 min; 100–30% B, 14 min; 30% B, 15 min.
The mass spectrometer was operated in negative multiple-reaction mode (MRM). The parameters were set as follows: IonSpray Voltage (−4500 V), Curtain Gas (35 psi), Ion Source Temp (550 °C), Ion Source Gas of 1 and 2 (60 psi).

2.3. Data Analysis

Microsoft Excel 2021 was used for statistics analysis, with Origin 2022 used to plot bar and dot line graphs. TBtools-II (V 2.0) software developed for multidimensional omics data visualization was used to conduct heatmap analysis. The sphericity assumption was assessed using Mauchly’s test (W = 0.000), which indicated a severe violation of the sphericity assumption. Therefore, the Greenhouse–Geisser correction was applied to adjust the degrees of freedom. Subsequent analysis using Bonferroni post hoc tests revealed a highly significant interaction between time and cultivar (p < 0.0001). This significant interaction precluded the direct interpretation of the main effects, necessitating simple effects analysis. Principal component analysis (PCA) was performed on the macadamia nut developmental stage dataset (with three replicates per group) using SIMCA 14.1 software. The robustness of the model was evaluated based on the cumulative explained variance (R2X) and predictive ability (Q2), with acceptance thresholds set at R2X > 0.6 and Q2 > 0.5.

3. Results and Discussion

3.1. Macadamia Fruit Development

The whole process from the withering of the female flower stigma to the yellowing and dehiscence of the involucre and maturation of the fruit was defined as the fruit development. As shown in Figure 1, the macadamia fruit development could be divided into four stages according to the morphological changes.
At stage 1 (50 DAF), the fruit diameter was approximately 1.5–2 cm. For ‘A4’ fruit, the inner part was yellowish-green, the fruit was wrapped by distinct strips of fibers, and the endosperm looked like a transparent paste that essentially filled the entire cavity. For ‘OC’, the inner shell was pale yellow, the outer shell was white, and the creamy-white kernel was distinctly visible. The shells were formed but remained soft for both ‘A4’ and ‘OC’.
At stage 2 (65 DAF), the fruit diameter was approximately 2.5–3 cm, with light brown inner shells, thickened shells, and plump and creamy-white kernels. The transverse and longitudinal sections of ‘A4’ showed that the kernel shape was formed. The ‘OC’ fruit was slightly convex at the top and concave at the bottom, with obvious glossiness.
At stage 3 (80 DAF), the fruit diameter was approximately 3.5–4 cm. The outer pericarp became thin, the inner layer was yellowish brown in color, and the shell was hardened. The kernel was milky white with a hard and crunchy feel. The ‘A4’ shell had a lighter color than the ‘OC’ shell.
At stage 4 (140 DAF), the fruit diameter was approximately 3.5–4 cm. The outer pericarp turned dark green, the shell was dark brown and solid, and the kernel was filled. The shell and outer pericarp were slightly separated. At this time, the development of fruit morphology and appearance was similar to that at maturity, which is the same as that reported by Xu & Li [20].

3.2. Dynamic Changes in Green Fruit Weight and Shell Fruit Weight During Growth of Macadamia

There was a general trend (Figure 2) of change from rapid growth to slow, steady growth in the weight of the ‘A4’ and ‘OC’ macadamia green-skinned fruit and shelled fruit [21]. The fresh fruit weight of ‘A4’ and ‘OC’ differed significantly only in relation to developmental time, which indicates that their patterns of change over time are similar. In contrast, shell weight showed a highly significant time (developmental stage) × cultivar interaction (p < 0.001), suggesting that the change in shell weight across developmental stages is distinct for different cultivars (Tables S1 and S3). Specifically, ‘A4’ and ‘OC’ showed rapid increases in the weight of their green-skinned and shelled fruit from 50 DAF to 65 DAF, with ‘A4’ increasing by 6.7 g and 6.65 g, and ‘OC’ increasing by 5.96 g and 2.76 g. ‘A4’ fruit weight showed slow growth from 65 DAF to 125 DAF and stable growth thereafter. The fruit growth of ‘OC’ was slow from 65 DAF to 95 DAF and stable after 95 DAF, when the weight increased by 1.1–3.18 g and 0.47–2.3 g for green and shell fruit, respectively. The weight change observed during the stable period was approximately 0.1 g, indicating that ‘OC’ matures prior to ‘A4’. In Figure 2B, the slight decrease in the shell fruit weight of ‘OC’ between 95 DAF and 110 DAF may be due to the heavier weight of the pericarp.

3.3. Dynamics of Longitudinal and Transverse Diameters and Fruit Shape Index of Macadamia During Growth

The interaction between time (developmental stage) and cultivar had a highly significant effect (p < 0.001) on the longitudinal and transverse diameter of fruits with green exocarps, the longitudinal and transverse diameter of shell fruits, and the shape index of fruits with green exocarps and shell fruits. This indicates significant differences in the developmental stage of these fruit quality metrics between ‘A4’ and ‘OC’. Significant cultivar differences between ‘A4’ and ‘OC’ were consistently found across all developmental stages in the longitudinal diameter of fruits with green exocarps and the transverse diameter of shelled fruit. There was no significant difference in shell longitudinal diameter at 65 DAF between ‘A4’ and ‘OC’, and significant cultivar differences existed at the other six developmental stages. The shelled fruit transverse diameter showed no significant difference between ‘A4’ and ‘OC’ at 65 DAF and 80 DAF (Tables S2 and S3). Specifically, the longitudinal and transverse diameters of the green and shelled macadamia nuts showed consistent trends with single fruit weight. Single ‘A4’ green-skinned and shelled fruits showed rapid growth in both longitudinal and transverse diameter from 50 DAF to 65 DAF, slow growth from 65 DAF to 125 DAF, and stable growth after 125 DAF. The ‘OC’ green-skinned and shelled fruit exhibited rapid growth in both longitudinal and transverse diameter from 50 DAF to 65 DAF, slow growth from 65 DAF to 95 DAF, and stable growth thereafter, with generally no change in longitudinal and transversal meridian in the final period, which is in agreement with the results of Stephenson et al. [22] and Sakai et al. [23].
The shape index of the fruits with green peel displayed no significant difference from 80 to 110 DAF, signifying that the index’s change was not pronounced during this interval. Correspondingly, the shape index of the shelled fruit showed no significant difference from 95 to 140 DAF, suggesting that the fruit shapes of ‘A4’ and ‘OC’ had largely stabilized by this point. (Tables S2 and S3). Fruit shape index gradually decreased with fruit growth and development. In ‘A4’, the shape index of the green-skinned and shelled fruit ranged from 1.64 to 1.29 and 1.29 to 1.07, respectively, from 50 DAF to 140 DAF after anthesis, with the shape of the green-skinned fruit ranging from oblong-ellipsoid to near-round, and that of shelled fruit ranging from ellipsoid to nearly round. The fruit shape index of the ‘OC’ green-skinned and shelled fruit ranged from 1.40 to 1.31 and 1.23 to 1.07, respectively, from 50 d to 140 d after anthesis, where the green-skinned fruit was ellipsoid with little variation in shape and the shelled fruit ranged from ellipsoid to nearly round [21,24] (Figure 3).

3.4. Changes in SFA, MUFA, and PUFA Contents During Growth and Development of Macadamia Kernels

It is crucial to study fatty acid accumulation during macadamia development in order to determine the optimal period of fatty acid accumulation in macadamia kernels. As shown in Supplementary Materials Table S4, there is a highly significant interaction (p < 0.001) between developmental stage and cultivar for fatty acid content, indicating that the patterns of fatty acid change between cultivars at different developmental stages. Figure 4A–C show the changing patterns of SFA, MUFA, and PUFA contents in the two cultivars throughout fruit development. The SFA content of ‘OC’ was significantly higher than that of ‘A4’ at 95 DAF. However, the SFA content of ‘A4’ showed a significantly higher value than ‘OC’ at 125 DAF. The MUFA content of ‘OC’ was significantly higher than ‘A4’ at 50 DAF. There were no significant differences in MUFA content at 65 DAF or 110 DAF. The PUFA content of ‘OC’ was significantly higher than ‘A4’ at 65 DAF and 95 DAF, while the PUFA content of ‘A4’ was significantly higher than ‘OC’ at 125 DAF. Overall, SFAs showed a decreasing trend with fruit growth and development, with MUFAs and PUFAs reaching their maximum values at 125 DAF and 140 DAF in ‘A4’ and at 95 DAF in ‘OC’, which is in agreement with the description of fatty acid changes in walnut development by Chunying Huang et al. [25]. The above results also indicated that the accumulation of fatty acids in ‘OC’ occurs slightly earlier than in ‘A4’, similar to the findings of Parcerisa et al. [26] and Han Shuquan et al. [27].
Based on the relevant literature, the physiological mechanisms of macadamia fatty acid biosynthesis are as follows (Figure 5): acetyl-CoA is converted to malonyl-CoA by acetyl-CoA carboxylase. Malonyl-CoA then serves as a substrate for fatty acid synthase, undergoing successive polymerization reactions within the chloroplast stroma to gradually synthesize 16- to 18-carbon saturated fatty acids [28]. Under the action of Δ9-desaturase (e.g., Stearoyl-Acyl Carrier Protein Desaturase), saturated fatty acids are converted into monounsaturated fatty acids. This explains the peak in MUFAs at 90 DAF and 125 DAF, followed by a gradual decline as the fruit matures. PUFAs exhibit the most rapid increase during the 65–125 DAF and 65–95 DAF stages, respectively. This suggests that Δ9-desaturase and FAD2 (ω-6 desaturase) possess high catalytic activity during fruit development and maturation [29].
Figure 4D shows the changes in total fatty acid content in ‘A4’ and ‘OC’ at different developmental stages. As shown in Supplementary Materials Table S4, a highly significant interaction (p < 0.001) was observed between developmental stage and cultivar for fatty acid content. The accumulation patterns of total fatty acids and MUFAs were similar. The fatty acid content of ‘A4’ linearly and rapidly increased from 50 to 65 DAF, followed by slow increases from 65 to 125 DAF, and then decreased until 140 DAF. ‘OC’ is an early-ripening variety. From late June to early July, which is a period of rapid fruit development, the total fatty acid content dramatically increased from 80 (232.16 μg/g) to 95 DAF (379.71 μg/g), which can be defined as a vital period for fatty acid accumulation for ‘OC’. ‘A4’ showed rapid accumulation of fatty acids from 80 (172.85 μg/g) to 125 (287.28 μg/g) DAF, and this period is therefore a critical period for fatty acid accumulation in ‘A4’. In addition, ‘A4’ showed a significantly greater accumulation of MUFAs than ‘OC’ from 110 to 140 DAF, which may be due to the favorable temperature and light conditions for the biosynthesis of fatty acids during this period [30].

3.5. Principal Component Analysis of Fatty Acid Fractions and Contents in Macadamia Kernels at Different Developmental Stages

PCA was performed to understand the fatty acid fractions and contents in the fruit of the two macadamia cultivars. PC1 accounted for 61.3% of the variance, while PC2 explained an additional 20.4% (cumulative 81.7%). As shown in Figure 5, for different developmental stages and cultivars, A4-A, A4-B, OC-A, and OC-B converged and were separated from the remaining combinations. In terms of PC1, there were significant positive correlations among A4-F, A4-G, OC-D, and OC-E, while there were significant negative correlations among A4-A, A4-B, OC-A, and OC-B. In terms of PC2, there were significant positive correlations among A4-A, A4-B, OC-A, and OC-B, while A4-C and OC-F were significantly negatively correlated with each other. A4-F and OC-D were dissociated from other periods, i.e., they were remarkably different from other periods, which is similar to the above results (Figure 6).

3.6. Heatmap Analysis of Fatty Acids in Macadamia Kernel at Different Developmental Stages

A heatmap analysis was performed for the fatty acid contents in ‘A4’ and ‘OC’ at seven developmental stages. The heatmap reveals that ‘A4’ showed high expressions of fatty acid content at 125 DAF, and fatty acids were highly expressed in ‘OC’ at 95 DAF during macadamia fruit development (Figure 7).
The four fatty acids with the highest abundance in macadamia fruit are oleic acid, palmitic acid, oleic acid, and palmitic acid, which is the same as in the findings of Aquino-Bolanos [31]. The ‘A4’ kernel oil samples had the highest content of oleic acid, followed by isoleic acid, palmitic acid, and finally palmitoleic acid. The ‘OC’ kernel oil samples had the highest content of palmitoleic acid, followed by oleic acid(C18:1(n-9)), cis-Vaccenic acid(C18:1(n-7)), and finally palmitoleic acid (C16:1). These results support the previous finding that fatty acid content varies between different macadamia varieties [15].
The interaction between time and variety had a statistically significant effect on the four fatty acids (p < 0.001). Palmitic acid (C16:0) showed no significant difference between ‘A4’ and ‘OC’ at 65 DAF and 80 DAF, indicating a similar accumulation pattern for both during this period. The palmoleic acid (C16:1) content in ‘OC’ was significantly higher than in ‘A4’ at 50, 65, 80, and 95 DAF (p < 0.05). Conversely, ‘A4’ showed significantly higher palmoleic acid levels than ‘OC’ at 140 DAF (p < 0.01), suggesting a crossover interaction. Oleic acid (C18:1n9) expression in ‘OC’ was significantly higher than in ‘A4’ at 95 DAF (p < 0.05), but no significant differences were observed at other time points, indicating a synchronized accumulation pattern. Significant differences were observed between ‘OC’ and ‘A4’ for cis-oleic acid (C18:1n7) levels at 95 DAF and 125 DAF (p < 0.05) (Tables S5 and S6). Figure 8 shows the accumulation of oleic acid (C18:1(n-9)), palmitic acid (C16:1), cis-Vaccenic acid (C18:1(n-7)), and hexadecanoic acid (C16:0) at different developmental stages, among which oleic acid and palmitoleic acid showed the most significant increases. ‘A4’ exhibited a slow accumulation of oleic acid from 50 to 65 DAF and rapid accumulation from 65 to 125 DAF, followed by decreases until 140 DAF, while in ‘OC’, the oleic acid content decreased from 50 to 65 DAF, but rapidly increased from 65 to 95 DAF, which was the same as the total fatty acid accumulation, as shown in Figure 4D. Molecular-level analysis revealed that the activities of vital enzymes in the fatty acid biosynthesis pathway of macadamia kernels were altered with fruit development, as reported by Liu et al. [32]. They reported that acetyl-CoA carboxylase was upregulated at 154 and 172 DAF compared with 65 and 94 DAF, whereas it was downregulated at 139 DAF compared with 124 DAF.
The palmitoleic acid content in ‘A4’ and ‘OC’ had decreased at 80 DAF compared with that at 65 DAF, but was followed by a sharp increase at 95 DAF, which may be related to changes in the enzymes controlling the fatty acid synthesis pathway. According to Gao Wenya [33], the expression of stearoyl ACP desaturase 6 (SAD6), an enzyme that regulates the biosynthesis of unsaturated fatty acids, increased gradually from 30 to 50 DAF, remained at a high level during 50–63 DAF, and then decreased from 63 to 73 DAF. This changing trend is generally consistent with the observed changes in palmitoleic acid content in ‘A4’ and ‘OC’.
‘A4’ and ‘OC’ had relatively higher contents of palmitic acid in the early stage of fruit development, and the content of SFAs gradually decreased with fruit development. It has been found that in the fatty acid biosynthesis process of oil crops at maturity, SDA (Stearoyl-ACP Desaturase), AD6 (Acyl-ACP Desaturase 6), FAD7 (Fatty Acid Desaturase 7), FAD8 (Fatty Acid Desaturase 7), FAD2 (Fatty Acid Desaturase 2), and FAD3 (Fatty Acid Desaturase 3) in the endoplasmic reticulum can introduce double bonds to transform saturated fatty acids to unsaturated fatty acids to form oleic acid, linoleic acid, and linolenic acid. Therefore, the regulation of these genes may contribute to the decrease in palmitic acid and increase in unsaturated fatty acids in ‘A4’ and ‘OC’ [34,35].

3.7. Changes in Fatty Acid Composition in Macadamia Kernels at Different Developmental Stages

We further examined the fatty acid composition in ‘A4’ and ‘OC’ at different development stages. A total of 41 fatty acids were detected, as shown in Supplementary Materials Tables S7 and S8. There were 13 SFAs, 18 MUFAs, and 10 PUFAs, which accounted for 31.7%, 43.9%, and 24.4% of the total fatty acids, respectively. The MUFAs had the highest content, among which oleic acid C18:1(n-9) in ‘A4’ and ‘OC’ accounted for 20.99% and 19.77% of the total fatty acids, respectively; palmitoleic acid C16:1 accounted for 17.20% and 22.90%; and cis-Vaccenic acid C18:1(n-7) accounted for 20.06% and 19.00%. The highest content of palmitic acid among the SFAs accounted for 19.34% and 16.48% of the total fatty acids, followed by octadecanoic acid at 10.35% and 7.69%.
In the early fruit development stage, the SFA content in macadamia fruit is higher than the MUFA content; however, with the development of fruit, the MUFA content gradually increases, while the SFA content gradually decreases. This phenomenon may be due to the gradual increase in the activity of enzymes related to the fatty acid biosynthesis pathway with fruit development, which promotes the synthesis of MUFAs [36].

4. Conclusions

The present study revealed that the fruit morphology and fatty acid contents of different macadamia cultivars differ significantly at various developmental stages. In the process of growth and development, the single fruit weight and longitudinal and transverse diameter always showed a ‘fast–slow–stable’ growth trend, accompanied by gradual decreases in fruit shape index. The total fatty acid content of ‘OC’ was significantly greater than that of ‘A4’ from 80 to 110 DAF, but an opposite trend was observed from 110 to 140 DAF. Compared with ‘A4’, ‘OC’ had significantly higher contents of SFAs and MUFAs but a lower content of PUFAs. A total of 41 fatty acids were detected in the two macadamia cultivars at seven developmental stages, and their contents followed the order of MUFAs > SFAs > PUFAs. The fatty acid content increases with fruit ripening to reach the peak and then gradually decreases thereafter, particularly that of MUFAs. However, it is worth noting that different macadamia cultivars may differ in developmental timing and fatty acid accumulation due to varietal differences.
As a preliminary study, these results indicate a significant difference in the developmental timing of kernel fatty acid content in two major macadamia varieties cultivated in Yunnan, ‘OC’ and ‘A4,’ during their development. Future research can further establish a correlation model between fatty acid content and fruit flavor. This will allow us to scientifically determine the optimal harvest time based on market demands, ultimately optimizing the processing quality and flavor characteristics of macadamia.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy15071682/s1, Table S1: Fresh fruit and shell fruit weight analysis of variance; Table S2: Morphological indicator analysis of variance; Table S3: ‘A4’ vs. ‘OC’ analysis of developmental significance; Table S4: Fatty acid content analysis of variance; Table S5: Hexadecanoic acid, cis-Vaccenic acid, palmitoleic acid, and oleic acid content analysis of variance; Table S6: ‘A4’ vs. ‘OC’ analysis of developmental significance; Table S7: Changes in fatty acids during development of ‘A4’ macadamia (mean ± standard deviation). Table S8: Changes in fatty acids during development of ‘OC’ macadamia (mean ± standard deviation). Figure S1: Fatty acid XIC chart.

Author Contributions

M.C.: Writing—Original Draft, Methodology, Formal Analysis, Data Curation, Conceptualization; B.Z.: Writing and Editing, Methodology, Formal Analysis, Data Curation, Conceptualization; M.D.: Data Curation, Resources, Software, Validation; H.Z.: Writing—Review, Supervision, Project Administration, Software; S.Y.: Software, Validation, Formal Analysis, Visualization. F.Y.: Resources, Software, Supervision, Visualization; W.S.: Software, Visualization, Supervision, Validation; X.F.: Data Curation, Resources, Software, Supervision; H.Y.: Resources, Supervision, Validation, Software; J.L.: Writing—Review, Resources, Supervision, Validation; X.Z.: Resources, Project Administration, Investigation, Funding Acquisition, Conceptualization. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Technical Innovation Talents Project of Yunnan Province (No. 202105AD160049); The Lincang Science and Technology Bureau’s 2024 Science and Technology Innovation Empowering High-Quality Economic Development Special Project—Research on the Standard System of the Lincang Macadamia Nut Whole-Industry Chain (No.2024LCTEC002); and the Lincang Sustainable Development Agenda Innovation Demonstration Zone Science and Technology Project (No. 202304AC10001-A01).

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author.

Acknowledgments

We thank Zuoxiong Liu (Huazhong Agricultural University) for his advice on this manuscript.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Development of macadamia. Note: ‘A4’ and ‘OC’ represent two different varieties of macadamia nuts, and Figure 1, from left to right, shows macadamia development at 50, 65, 80, 95, 110, 125, and 140 DAF.
Figure 1. Development of macadamia. Note: ‘A4’ and ‘OC’ represent two different varieties of macadamia nuts, and Figure 1, from left to right, shows macadamia development at 50, 65, 80, 95, 110, 125, and 140 DAF.
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Figure 2. Changes in fruit weights during growth and development of ‘A4’ and ‘OC’ macadamia. (A) Green fruit weight; (B) Shelled fruit weight; Note: Error bars in figure calculated by SD (same below).
Figure 2. Changes in fruit weights during growth and development of ‘A4’ and ‘OC’ macadamia. (A) Green fruit weight; (B) Shelled fruit weight; Note: Error bars in figure calculated by SD (same below).
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Figure 3. Developmental changes in fruit morphology of ‘A4’ and ‘OC’ macadamia cultivars. (A) Transverse diameter of fruits with green exocarp; (B) Transverse diameter of fruits with green exocarp; (C) Longitudinal diameter of shell fruit; (D) Transverse diameter of shell fruit; (E) Fruit Shape Index of Fruits with Green exocarp; (F) Fruit shape index of shell fruit; For designations, see Figure 2.
Figure 3. Developmental changes in fruit morphology of ‘A4’ and ‘OC’ macadamia cultivars. (A) Transverse diameter of fruits with green exocarp; (B) Transverse diameter of fruits with green exocarp; (C) Longitudinal diameter of shell fruit; (D) Transverse diameter of shell fruit; (E) Fruit Shape Index of Fruits with Green exocarp; (F) Fruit shape index of shell fruit; For designations, see Figure 2.
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Figure 4. Changes in fatty acid content of ‘A4’ and ‘OC’ macadamia kernels, respectively, during growth and development. (A) SFA content; (B) MUFA content; (C) PUFA content; (D) Fatty acid content; Data shown as mean ± SD. Significant differences denoted as * p < 0.05; ** p < 0.01; and **** p < 0.0001, and ‘ns’ denotes ‘not significant’.
Figure 4. Changes in fatty acid content of ‘A4’ and ‘OC’ macadamia kernels, respectively, during growth and development. (A) SFA content; (B) MUFA content; (C) PUFA content; (D) Fatty acid content; Data shown as mean ± SD. Significant differences denoted as * p < 0.05; ** p < 0.01; and **** p < 0.0001, and ‘ns’ denotes ‘not significant’.
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Figure 5. The accumulation of fatty acids in the ‘A4’ and ‘OC’ macadamia kernels was divided into three stages: early, mature, and late-mature stages. C16:0: palmitic acid, C18:0: stearic acid, C18:1: oleic acid, C18:2: linoleic acid, C20:2: arachidonic acid; Elo: Elongase; Δ9Des: Δ9 desaturase; FAD2: ω-6 desaturase; FAS: fatty acid synthesis; SFA: saturated fatty acid; MUFA: monounsaturated fatty acid; PUFA: polyunsaturated fatty acids.
Figure 5. The accumulation of fatty acids in the ‘A4’ and ‘OC’ macadamia kernels was divided into three stages: early, mature, and late-mature stages. C16:0: palmitic acid, C18:0: stearic acid, C18:1: oleic acid, C18:2: linoleic acid, C20:2: arachidonic acid; Elo: Elongase; Δ9Des: Δ9 desaturase; FAD2: ω-6 desaturase; FAS: fatty acid synthesis; SFA: saturated fatty acid; MUFA: monounsaturated fatty acid; PUFA: polyunsaturated fatty acids.
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Figure 6. PCA of fatty acid profiles in two macadamia kernels ‘A4’ (triangles) and ‘OC’ (circles) during development. Developmental stages represented by letters and colors: A = 50 DAF (red), B = 65 DAF (orange), C = 80 DAF (yellow), D = 95 DAF (green), E = 110 DAF (black), F = 125 DAF (blue), G = 140 DAF (purple).
Figure 6. PCA of fatty acid profiles in two macadamia kernels ‘A4’ (triangles) and ‘OC’ (circles) during development. Developmental stages represented by letters and colors: A = 50 DAF (red), B = 65 DAF (orange), C = 80 DAF (yellow), D = 95 DAF (green), E = 110 DAF (black), F = 125 DAF (blue), G = 140 DAF (purple).
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Figure 7. Heat maps of fatty acids in‘A4’ and ‘OC’ macadamia kernels at different developmental stages (A4 left, OC right) Note: A, B, C, D, E, F, and G represent 50 DAF, 65 DAF, 80 DAF, 95 DAF, 110 DAF, 125 DAF, and 140 DAF, respectively. Fatty acid expression levels color-coded as follows: −2 (blue) indicates lowest expression, 0 (yellow) indicates moderate expression (no significant upregulation or downregulation), 2.5 (red) indicates highest expression.
Figure 7. Heat maps of fatty acids in‘A4’ and ‘OC’ macadamia kernels at different developmental stages (A4 left, OC right) Note: A, B, C, D, E, F, and G represent 50 DAF, 65 DAF, 80 DAF, 95 DAF, 110 DAF, 125 DAF, and 140 DAF, respectively. Fatty acid expression levels color-coded as follows: −2 (blue) indicates lowest expression, 0 (yellow) indicates moderate expression (no significant upregulation or downregulation), 2.5 (red) indicates highest expression.
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Figure 8. Accumulation of key fatty acids at different developmental stages of ‘A4’ and ‘OC’ macadamia.
Figure 8. Accumulation of key fatty acids at different developmental stages of ‘A4’ and ‘OC’ macadamia.
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MDPI and ACS Style

Cao, M.; Zhang, B.; Duan, M.; Zhang, H.; Yan, S.; Yang, F.; Shi, W.; Fu, X.; Yang, H.; Li, J.; et al. Dynamic Changes in Fatty Acids in Macadamia Fruit During Growth and Development. Agronomy 2025, 15, 1682. https://doi.org/10.3390/agronomy15071682

AMA Style

Cao M, Zhang B, Duan M, Zhang H, Yan S, Yang F, Shi W, Fu X, Yang H, Li J, et al. Dynamic Changes in Fatty Acids in Macadamia Fruit During Growth and Development. Agronomy. 2025; 15(7):1682. https://doi.org/10.3390/agronomy15071682

Chicago/Turabian Style

Cao, Mingqun, Birong Zhang, Minxian Duan, Hanyao Zhang, Suyun Yan, Fan Yang, Wenbin Shi, Xiaomeng Fu, Hongxia Yang, Jinxue Li, and et al. 2025. "Dynamic Changes in Fatty Acids in Macadamia Fruit During Growth and Development" Agronomy 15, no. 7: 1682. https://doi.org/10.3390/agronomy15071682

APA Style

Cao, M., Zhang, B., Duan, M., Zhang, H., Yan, S., Yang, F., Shi, W., Fu, X., Yang, H., Li, J., & Zhou, X. (2025). Dynamic Changes in Fatty Acids in Macadamia Fruit During Growth and Development. Agronomy, 15(7), 1682. https://doi.org/10.3390/agronomy15071682

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