A comprehensive study of raw and roasted macadamia nuts: Lipid profile, physicochemical, nutritional, and sensory properties (2024)

This research provided a deep insight into the quality control of macadamia nuts during roasting and would help set guidelines for selecting the suitable roasting conditions for macadamia nuts.

2.1. Chemicals and reagents

HPLC‐grade hexane, acetonitrile (ACN), 2‐propanol, chloroform (CHCl₃), methanol (MeOH), ammonium hydroxide (>25%), formic acid (>99%), acetic acid (>99%), heptadecanoic acid, and ammonium acetate were from CNW (Düsseldorf, Germany). Triethylamine (TEA) and N,N‐diethyl‐1,2‐ethanediamine (DEEA) were from Shanghai Aladdin Reagent Co., Ltd. 2‐Chloro‐1‐methylpyridinium iodide (CMPI) was from Sinopharm Chemical Reagent Co., Ltd. 1,2,3‐Tri‐(heptadecenoyl)‐glycerol (TAG‐17:1/17:1:/17:1) was from Avanti Polar Lipids, Inc. (Alabama, USA). Other standards were from Sigma‐Aldrich (St. Louis, MO, USA), unless otherwise stated. Other reagents were analytical grade from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ultra‐pure water (Milli‐Q, Millipore, Bedford, MA, USA) was used for all experiments.

2.2. Preparation of dried raw and roasted materials

Two major varieties of macadamia nuts in China, Guire 1 and Own Choice (O.C), were obtained from the National Field Genebank for Tropical Fruits, South Subtropical Crops Research Institute, Chinese Academy of Tropical Agricultural Sciences. The nuts were dehusked within 24hr of harvest. Nuts, in the shell, were then stored in polyethylene bags. Fresh nuts (15% dry basis moisture content, db) were stored at −18°C until needed. The nuts were taken out and equilibrated to room temperature for 3–4hr and then dried in an mechanical convection oven (SHT, Sanxiong Machinery Manufacture Co. Ltd., Shangyu, China) using a regime (hot air‐drying at 35℃ for 2days, 45℃ for 2days, 55℃ for 2days), as described previously (Walton etal.,²⁰¹³). The moisture content of the nuts was monitored, and the nuts were removed from the oven, when the moisture content had reached 1.5% (db) and designated as raw.

Dried raw nuts were roasted at 125°C for 15min using an electric rotary oven (X2R, Guangdong Galanz Group Co., Ltd., China), which reduced the moisture content to 1.0% (db), and these nuts were designated as roasted. These roasting conditions were selected based on the nut industry best practice, to avoid quality deterioration (Buthelezi etal.,²⁰¹⁹).

2.3. Microstructure analysis

For analysis of microstructure, the nut samples were examined by transmission electron microscopy (TEM, H‐7650, Hitachi, Tokyo, Japan), as described previously (Niu etal.,²⁰¹⁵). Briefly, the nut samples were fixed, washed and dehydrated, embedded in acetone and Spurr resin. Sections 70–90nm thick were cut from the embedded tissue using a microtome, double‐stained with uranyl acetate and lead citrate, and then examined.

2.4. Physicochemical property analysis

Acid value (AV) was determined by AOCS official method Cd 3a‐63 (AOCS, 2004). Peroxide value (PV) was determined by the AOAC 965.33 method (AOAC, 2005). Water activity (a_w) was measured with an Aqualab^® series 3 TE water activity meter (Decagon Devices Inc., Pullman, WA., U.S.A.).

The oxidative stability index (OSI) was determined in terms of the induction period (IP) with an 892 Professional Rancimat (Metrohm, Switzerland). The nut sample (0.5g) was heated to 120°C in a reaction tube and subjected to air inflow of 20 L/h. IP was automatically calculated by the instrument's software. Three readings per sample were taken and averaged. Moisture content (AOAC method 925.40), total fat (AOAC method 948.22), ash (AOAC method 950.49), total dietary fiber (AOAC method 985.29), and crude protein (AOAC method 950.48) (AOAC, 2005) were also determined. The total carbohydrate content was calculated by subtracting the sum of the crude protein, total fat, water, and ash from the total weight of the nut flour (Birch etal.,²⁰¹⁰).

2.5. Lipid concomitants analysis

Ground macadamia nut kernels (3g) were extracted with hexane/isopropanol (9ml, 3:2 v/v) under vigorous stirring for 15min and then filtered under vacuum. The filter residue was re‐extracted twice with hexane/isopropanol (3:2) and then dried with anhydrous sodium sulfate. The filtrate was centrifuged at 8,983g for 10min. The extracts were dried under N₂ to yield an oil. The sterol, tocopherol, tocotrienols, thiamine, and squalene contents were analyzed as described previously (Wall,²⁰¹⁰) by HPLC.

The total phenolic content was determined spectrophotometrically using Folin–Ciocalteu reagent at 750nm, with gallic acid monohydrate as a standard and expressed as mg gallic acid equivalents (GAE) kg^‐1 of dry weight, as described previously (Buthelezi etal.,²⁰¹⁹).

2.6. Analysis of fatty acid composition

Macadamia nuts were cold‐pressed (CA59G press, IBG Monforts, Nuremberg, Germany) at room temperature. After centrifugation at 8,983g for 20min, the oil was transferred to a brown glass container, kept at 4℃, and analyzed within 1week. A standard procedure with KOH/methanol solution (0.4mol/L) was used to prepare fatty acid methyl esters (FAMEs) from the oil (Xie etal.,²⁰¹⁹; Xu etal.,²⁰¹⁸). The FAMEs were analyzed by gas chromatography (Agilent Technologies 7890A, Santa Clara, CA) coupled with a capillary column (HP‐FFAP, 30m×0.25mm×0.25μm, Agilent) and a flame ionization detector (FID). Sample (1.0μl) was injected in splitless mode. The carrier gas was nitrogen with an inlet pressure of 1.7×10⁵Pa. The oven temperature was maintained at 210°C for 1.0min, then ramped to 230°C at 10°C/min, and then held for 7min. The temperatures of the injection port and detector were maintained at 250 and 280°C, respectively. The relative content (% w/w) of each FA was calculated (peak area of each fatty acid/peak area of total fatty acids). Heptadecanoic acid (17:0, 70μl, 5.15mg/ml) was used as the internal standard to quantify individual fatty acids.

2.7. Shotgun‐NL‐ESI‐MS/MS for the analysis of TAGs

Triacylglycerols (TAGs) were determined as described previously (Xie etal.,²⁰¹⁹). Briefly, an aliquot (25mg) of each nut oil sample was dissolved in n‐hexane and diluted to 10mg/ml. An aliquot (20μl) of hexane solution was transferred to a glass culture tube, to which the internal TAG standard (17:1/17:1/17:1, 0.1mg/ml in methanol, 10μl) was added. Methanol (450μl), chloroform (450μl), and NH₄OH (10%, 100Μl) were added sequentially and then vortexed for 1min. The TAG analysis was performed on a shotgun‐ESI‐MS/MS system consisting of a 4,000 Q‐Trap mass spectrometer (AB Sciex, Toronto, Canada) with an ESI source in positive mode.

The TAGs were detected as ammonium ions, [M+NH₄]⁺, by a series of neutral loss (NL) scans. The scans targeted losses of fatty acyl chains as neutral fragments with NH₃, including NL285.3 (17:1), NL245.3 (14:0), NL273.3 (16:0), NL271.3 (16:1), NL297.3 (18:2), NL299.3 (18:1), NL301.3 (18:0), NL327.3 (20:1), NL329.3 (20:0), and NL357.3 (22:0), NL385.3 (24:0). The collision gas was nitrogen and the collision energy +25eV. The collision gas pressure was set on “low.” The declustering potential was +100V, the entrance potential +14V, and the exit potential +14V. The source temperature (heated nebulizer) was 100°C. The curtain gas was set at 20 psi; and the two ion source gases were set at 45 psi. The electrospray capillary voltage was +5.5kV. The mass spectrum was scanned in the range m/z 500–1200.

2.8. Chemical derivatization coupled with NLS‐ESI‐MS/MS for the analysis of FFAs

Determination of FFAs in oil samples was achieved using DEEA derivatization and analysis by shotgun‐ESI‐MS/MS (as above). Derivatives of FFAs were detected using the NL method (NLS 73Da) in positive‐ion mode, as described previously (Liu etal.,²⁰¹⁸). Briefly, an aliquot (10mg) of each oil sample was dissolved in n‐hexane and diluted to 0.1mg/ml. An aliquot (20μl) of diluted oil sample, internal standard (heptadecenoic acid, C17:1, 1μmol/L in CAN, 10μL), ACN (850μl), TEA (20μmol/ml, 30μl), and CMPI (20μmol/ml, 20μl) was added sequentially and vortexed for 1min. Finally, DEEA (20μmol/ml, 50μl) was added to label the FFAs. The derivatizing reaction was performed in an ultrasonic bath (Ultrasonic Cleaner, Jeken Ultrasonic Cleaner Limited, China), for 5min at 40°C. The ultrasound frequency and power were 40kHz and 500W, respectively. The resultant mixture was dried under nitrogen gas, and then, CHCl₃ (1ml) and formic acid–water (2ml, 10:90 v/v) were added. After vortexing the sample for 2min, the upper phase was removed and the extraction step repeated three times. Finally, the chloroform phase was dried under a stream of nitrogen and redissolved by ACN (1ml). The collision energy (CE) and declustering potential (DP) were set at +32V and +75V. Collision energy spread and collision cell exit potential were all set at 10V. The curtain gas pressure was 20 psi, and the two ion source gases were set at 40 psi. The mass spectrum scanning was operated in the range of m/z 200–500.

2.9. Sensory evaluation

Sensory evaluation was carried out as described previously (Buthelezi etal.,²⁰¹⁹). The panelists (10 males and 10 females) ranging from the age of 30 to 50 were requested to evaluate the sensory attributes of “Guire 1” and “O.C” kernels, including their texture, aroma, rancid taste, and overall appearance. The quality of kernels was rated using the hedonic scale; the specific evaluation criteria are shown in Table1. After scoring, the average value of each index is used for analysis of variance by SPSS 21.0 software (SPSS Inc., Chicago, IL).

2.10. Data and statistical analysis

The mass data acquisitions were performed using Analyst 1.5 software (AB Sciex, USA) and Lipidview software ((AB Sciex, USA) for peak extraction and analysis of the acquired data. All experiments were performed in triplicate. The statistical analysis was performed by using SPSS 21.0 (SPSS Inc., USA). One‐way analysis of variance (ANOVA) with Duncan's multiple range test was used for multiple comparisons, and differences between two groups were evaluated using the Student's t tests. Differences among groups were considered statistically significant at p<0.05. All the figures with means and standard deviations for all values were computed in GraphPad prism 6.

3.1. Changes in microstructure after roasting

Transmission electron microscopy imaging of raw nuts (Figure1a) showed a regular structure with spherical protein bodies (PB), surrounded by much smaller, well‐defined, spherical oil bodies (OB). After roasting, the membrane structure of the oil bodies was disrupted, resulting in an apparently continuous oil phase, the cell wall (CW) boundary became fuzzy and irregular and the oil bodies, and protein bodies coalesced. The images clearly demonstrate that roasted treatment disrupts the membranes of oil bodies as well as other intracellular organelles, which makes the oil spill more easily (Niu etal.,²⁰¹⁵). Roasting resulted in an improvement in lipid extractability; the crude fat content of both varieties apparently increased by 2% (Table1). Incorporation of roasting in standard oil extraction methods markedly increased lipid extraction efficiency (Yoshida etal.,²⁰⁰⁶).

3.2. Physicochemical properties of raw and roasted nuts

The effects of roasting on the composition of macadamia nuts were determined (Table2). The moisture content of both varieties decreased from ~1.5 to 1%, the water activity of Guire 1 decreased from 0.62 to 0.38, and that of O.C decreased from 0.60 to 0.36. Water activity has a great influence on product storage stability and may cause changes in texture, color, flavor, aroma, stability, and acceptability, of both processed and raw nuts. The optimum water activity for storage of macadamia nuts is less than 0.53 at 25°C (Pankaew etal.,²⁰¹⁶). Roasting of macadamia nuts, therefore, reduces their water activity to within the optimum range for storage stability.

The acid value (AV) and peroxide value (POV) have been adopted as primary indicators of hydrolytic rancidity and hydroperoxide formation in tree nuts, during the initial phases of lipid oxidation (Sinanoglou etal.,²⁰¹⁴; Wang, Zhang, Johnson, etal.,²⁰¹⁴). In addition, they are important indicators of shelf life. There was a significant increase in the peroxide and acid values of both varieties after roasting (Table2). However, the after‐roasting values were still well below the upper limits (PV≤3meq/kg, AV≤3mg KOH/g) of the Chinese National Standard (GB 19300‐2014) and the UNECE Standard DDP‐23, Macadamia Kernels[S] (2011). In addition, the oxidative stability index (OSI) of the roasted nuts was greatly improved. This results from the Maillard browning reaction between sugars and amino acids (Chang etal.,²⁰¹⁶), which can improve antioxidant capacity (Ng etal.,²⁰¹⁴).

3.3. Nutritional components in raw and roasted nuts

Roasting moderately decreased the measured crude protein, crude fiber, and carbohydrate contents of Guire 1 and O.C (Table2). In particular, roasting does not change the content of anything, apart from moisture, but it does change the measurable, or available content, by changing extractability. From the results in Table2, there was significant change in the other nutritional components after roasting. The increase in available oil content indicated that the fat component of the nut kernel flour was largely removed during protein bodies coalesced. However, the roasted nuts were lower in moisture, crude fiber, ash, and crude protein, but higher in carbohydrate when compared to the respective dried raw sample (Table2).

The available sterol content increased by 13.1% in Guire 1 and 20.6% in O.C after roasting (p<.05) (Table3), and the total available phenolic contents increased significantly (p<.05), by 25.6% in Guire 1 and 19.4% in O.C. Roasting significantly increased the available levels of sterols and polyphenols, in agreement with previous reports, and appears to result from increased extractability of the isoforms because of heat treatment. These changes are accompanied by migration of some lipid species within the cell and improved bioavailability of some minor components (Moghaddam etal.,²⁰¹⁶; Sinanoglou etal.,²⁰¹⁴). The thiamine content in macadamia nuts was the highest reported for tree nuts, although roasting resulted in a moderate decrease in thiamine content in Guire 1, by 16.2% and in O.C by 17.8%, consistent with an earlier report (Stuetz etal.,²⁰¹⁷).

Roasting of nuts promotes cellular swelling and rupture; for example, considerable swelling of the cell wall and middle lamella of roasted almonds resulted in improved release of lipids from intact cell walls during digestion, indicating that diffusion of enzymes, bile salts, and lipid products into nut material in the GI tract may be facilitated by roasting (Bolling etal.,²⁰¹⁰). The yield of soluble phenolic extracts from macadamia nut kernels significantly increased after roasting; the same result was found in cashew nuts (Chandrasekara & Shahidi,²⁰¹¹).

3.4. Analysis of lipid composition in raw and roasted nuts

Gas chromatography (GC) analysis identified 11 FAs in macadamia nuts (Table4) and the FA compositions of raw and roasted nuts were consistent with a previous report (Sinanoglou etal.,²⁰¹⁴). The fatty acid profile mainly consisted of monounsaturated fatty acids (MUFA), predominantly oleic acid (C18:1 n‐9) and palmitoleic acid (C16:1 n‐7) acids, along with substantial proportions of the saturated palmitic acid (C16:0) and stearic acid (C18:0). In general, fatty acid percentages decreased in the order of monounsaturated>saturated>polyunsaturated (MUFA>SFA>PUFA), consistent with a previous report (Xu etal.,²⁰¹⁸). There was no difference in FA composition between raw and roasted nuts, but that did not necessarily mean there were no differences in the TAG or FFA profiles. Thus, further analysis was performed.

The shotgun lipidomics approach identified 38 lipid molecular species in macadamia nuts, which were characterized and quantified, including 28 TAGs and 10 FFAs (Figure2a). The two varieties of macadamia nuts contained the same amounts of triglycerides, and the fatty acid composition in the TAGs was consistent with the GC analysis results except for C24:0. This may result from greater sensitivity of MS, compared with GC, so the former can detect some trace fatty acids. The most abundant TAG species of raw dried and roasted macadamia nuts were OOO (1,2,3‐trioleic acid‐triglyceride), OOP_O (1,2‐oleic acid, 3‐palmitoleic acid‐triglyceride), OOP (1,2‐oleic acid, 3‐palmitate‐triglyceride), and P_OOP_O (1,3‐ palmitoleic acid, 2‐oleic acid‐ triglyceride), the contents >50mg/g, which is consistent with previous reports (Sinanoglou etal.,²⁰¹⁴). The total TAG content of the two varieties decreased slightly after roasting, but there was no significant difference. TAG is the main component of macadamia nut oil, accounting for 97.5% and has a great impact on the function and nutritional characteristics of the nut oil. In summary, roasting had a negligible effect on TAG content or composition.

Ten FFAs were quantified, the most abundant being oleic acid (C18:1), followed by linoleic acid (C18:2), then palmitoleic acid (C16:1) (Figure2b). Very small amounts of myristic acid (C14:0) and tetracosanoic acid (C24:0) were also detected. The contents of most FFAs increased after roasting and the contents of palmitoleic acid (C16:1), oleic acid (C18:1), and linoleic acid (C18:2) increased significantly, for example, the C16:1 in Guire 1 from 280.95 to 577.95μg/g, the C18:1 in O.C from 819.14 to 1,308.87μg/g, the C18:1 in O.C from 819.14 to 1,308.87μg/g, the C18:1 in Guire 1 from 838.36 to 1,220.25μg/g, the C18:2 in O.C from 210.79 to 601.67μg/g, resulting from hydrolysis of TAGs into FFAs by lipase, or nonenzymic hydrolysis. FFAs liberated from TAGs were related to the fatty acid composition and positional distribution (Liu etal.,²⁰¹⁸). Fatty acids in the 2‐position of TAG molecules are more easily hydrolyzed to form FFAs (Lu etal.,²⁰¹⁹; Xie etal.,²⁰¹⁹). Generally, saturated FAs, especially C18:0, mostly occupied the 1 and 3 positions, whereas unsaturated FAs, particularly C18:1 and C18:2, were primarily concentrated in 2‐position of TAGs (Xie etal.,²⁰¹⁹). This explains the larger increases in the FFAs C18:1, C18:2, and C16:1. Since the total TAG content is more than 95.5% and the total FFA content is less than 0.15%. Therefore, even a small amount of TAG hydrolysis can cause a significant increase in FFA content during roasting (Sinanoglou etal.,²⁰¹⁴).

Lipid oxidation was used to evaluate postharvest quality of nuts during processing and storage, FFAs are more susceptible to oxidation than triglycerides (TAGs), and an FFA concentration exceeding 1% decreased the shelf life of hazelnuts with previous reports (Moscetti etal.,²⁰¹²). Therefore, the FFA levels are a more reliable quality indicator of macadamia kernels (Toth,²⁰¹⁷). From Figure2, Our results suggest that the production of the total FFAs from Guire 1 and O.C kernels was not accelerated significantly by high temperature, although the content of several unsaturated free fatty acids has increased. The low production of free fatty acids, despite the exposure of kernels to high temperature, was possibly because there was insufficient moisture in the kernels for lipid hydrolysis (Walton & Wallace,²⁰¹¹). The Australian Macadamia Society (AMS) considers 0.5% FFA acceptable of kernel quality standard for processors. Combined with the results of Table1, the quality and shelf life of macadamia nuts did not decrease after roasting.

3.5. Sensory evaluation

The sensory evaluation of raw and roasted macadamia nuts showed that the texture, aroma, and overall appearance of both macadamia cultivars had been significantly (p<.05) improved by the roasting process (Figure3). All members of sensory evaluation team expressed that both varieties of roasted kernels were crisp, delicate, and uniform in good color and aroma, whereas the dried raw kernels had a smooth texture and almost no aroma.

In particular, the taste and aroma scores more than doubled, whereas the increase in rancid taste (bitterness) was not noticeable, because the increased scores were still below 1, indicating that roasting did not produce detectable off‐flavors, in agreement with previous reports (Walton etal.,²⁰¹³). Moisture loss is considered to be the main factor in texture development of roasted kernels, leading to increased crispiness (Schlormann etal.,²⁰¹⁵). Kernels become crisper after roasting and are preferred by consumers (Liaotrakoon etal.,²⁰¹⁶). The roasting process is responsible for the development of the typical taste and the crunchy texture of macadamia nuts, resulting from structural and chemical changes, such as lipid oxidation and Maillard reactions (Fischer etal.,²⁰¹⁷; Liu etal.,²⁰¹⁸). The enhancement of aroma in roasted nuts can be attributed to the generation of aromatic compounds such as benzaldehyde, methylphenol, alcohol, and alkylbenzenes during roasting process (Fischer etal.,²⁰¹⁷). Maillard browning reaction and caramelization also promote the generation of flavor compounds (Poogungploy etal.,²⁰¹⁸). According to the sensory evaluation results, under the recommended roasting conditions, macadamia nuts undergo very little browning, have improved sensory quality, and are acceptable to consumers.

Table S1‐S2

• Arroyo‐Caro, J. M., Manas‐Fernandez, A., Alonso, D. L., & Garcia‐Maroto, F. (2016). Type I diacylglycerol acyltransferase (MtDGAT1) from Macadamia tetraphylla: Cloning, characterization, and impact of its heterologous expression on triacylglycerol composition in yeast. Journal of Agricultural and Food Chemistry, 64(1), 277–285. 10.1021/acs.jafc.5b04805. [PubMed] [CrossRef] [Google Scholar]
• Bailey, H. M., & Stein, H. H. (2020). Raw and roasted pistachio nuts (Pistacia vera L.) are 'good' sources of protein based on their digestible indispensable amino acid score as determined in pigs. Journal of the Science of Food and Agriculture, 100(10), 3878–3885. 10.1002/jsfa.10429 [PubMed] [CrossRef] [Google Scholar]
• Birch, J., Yap, K., & Silco*ck, P. (2010). Compositional analysis and roasting behaviour of gevuina and macadamia nuts. International Journal of Food Science and Technology, 45(1), 81–86. 10.1111/j.1365-2621.2009.02106.x [CrossRef] [Google Scholar]
• Bolling, B. W., Blumberg, J. B., & Chen, C. Y. O. (2010). The influence of roasting, pasteurisation, and storage on the polyphenol content and antioxidant capacity of California almond skins. Food Chemistry, 123(4), 1040–1047. 10.1016/j.foodchem.2010.05.058 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
• Bolling, B. W., Chen, C. Y. O., McKay, D. L., & Blumberg, J. B. (2011). Tree nut phytochemicals: Composition, antioxidant capacity, bioactivity, impact factors. A systematic review of almonds, Brazils, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts. Nutrition Research Reviews, 24(2), 244–275. 10.1017/S095442241100014X [PubMed] [CrossRef] [Google Scholar]
• Buthelezi, N. M. D., Magwaza, L. S., & Tesfay, S. Z. (2019). Postharvest pre‐storage processing improves antioxidants, nutritional and sensory quality of macadamia nuts. Scientia Horticulturae, 251, 197–208. 10.1016/j.scienta.2019.03.026 [CrossRef] [Google Scholar]
• Chandrasekara, N., & Shahidi, F. (2011). Oxidative stability of cashew oils from raw and roasted nuts. Journal of the American Oil Chemists Society, 88(8), 1197–1202. 10.1007/s11746-011-1782-3 [CrossRef] [Google Scholar]
• Chang, S. K., Alasalvar, C., Bolling, B. W., & Shahidi, F. (2016). Nuts and their co‐products: The impact of processing (roasting) on phenolics, bioavailability, and health benefits ‐ A comprehensive review. Journal of Functional Foods, 26, 88–122. 10.1016/j.jff.2016.06.029 [CrossRef] [Google Scholar]
• Chen, H., Wei, F., Dong, X. Y., Xiang, J. Q., Quek, S. Y., & Wang, X. M. (2017). Lipidomics in food science. Current Opinion in Food Science, 16, 80–87. 10.1016/j.cofs.2017.08.003 [CrossRef] [Google Scholar]
• Colzato, M., Scramin, J. A., Forato, L. A., Colnago, L. A., & Assis, O. B. G. (2011). 1h Nmr investigation of oil oxidation in macadamia nuts coated with zein‐based films. Journal of Food Processing and Preservation, 35(6), 790–796. 10.1111/j.1745-4549.2011.00530.x [CrossRef] [Google Scholar]
• Fischer, M., Wohlfahrt, S., Varga, J., Matuschek, G., Saraji‐Bozorgzad, M. R., Walte, A., & Zimmermann, R. (2017). Evolution of volatile flavor compounds during roasting of nut seeds by thermogravimetry coupled to fast‐cycling optical heating gas chromatography‐mass spectrometry with electron and photoionization. Food Analytical Methods, 10(1), 49–62. 10.1007/s12161-016-0549-8 [CrossRef] [Google Scholar]
• Hong, M. Y., Groven, S., Marx, A., Rasmussen, C., & Beidler, J. (2018). Anti‐inflammatory, antioxidant, and hypolipidemic effects of mixed nuts in atherogenic diet‐fed rats. Molecules, 23(12), doi:ARTN 3126. 10.3390/molecules23123126 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
• Hu, W., Fitzgerald, M., Topp, B., Alam, M., & O'Hare, T. J. (2019). A review of biological functions, health benefits, and possible de novo biosynthetic pathway of palmitoleic acid in macadamia nuts. Journal of Functional Foods, 62, 1–12. 10.1016/j.jff.2019.103520 [CrossRef] [Google Scholar]
• Le Lagadec, M. D. (2009). Kernel brown centres in macadamia: A review. Crop & Pasture Science, 60(12), 117–1123. 10.1071/CP08403 [CrossRef] [Google Scholar]
• Liaotrakoon, W., Namhong, T., Yu, C. H., & Chen, H. H. (2016). Impact of roasting on the changes in composition and quality of cashew nut (Anacardium occidentale) oil. International Food Research Journal, 23(3), 986–991. [Google Scholar]
• Lin, J. T., Liu, S. C., Hu, C. C., Shyu, Y. S., Hsu, C. Y., & Yang, D. J. (2016). Effects of roasting temperature and duration on fatty acid composition, phenolic composition, Maillard reaction degree and antioxidant attribute of almond (Prunus dulcis) kernel. Food Chemistry, 190, 520–528. 10.1016/j.foodchem.2015.06.004 [PubMed] [CrossRef] [Google Scholar]
• Liu, M., Wei, F., Lv, X., Dong, X. Y., & Chen, H. (2018). Rapid and sensitive detection of free fatty acids in edible oils based on chemical derivatization coupled with electrospray ionization tandem mass spectrometry. Food Chemistry, 242, 338–344. 10.1016/j.foodchem.2017.09.069 [PubMed] [CrossRef] [Google Scholar]
• Lu, X. W., Xiang, K. X., Zhou, W., Zhu, Y. R., He, Y., & Chen, H. (2019). Graphene‐like carbon derived from macadamia nut shells for high‐performance supercapacitor. Russian Journal of Electrochemistry, 55(3), 242–246. 10.1134/S1023193519020034 [CrossRef] [Google Scholar]
• Moghaddam, T. M., Razavi, S. M. A., Taghizadeh, M., & Sazgarnia, A. (2016). Sensory and instrumental texture assessment of roasted pistachio nut/kernel by partial least square(PLS) regression analysis: Effect of roasting conditions. Journal of Food Science and Technology‐Mysore, 53(1), 370–380. 10.1007/s13197-015-2054-2 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
• Moreno‐Perez, A. J., Sanchez‐Garcia, A., Salas, J. J., Garces, R., & Martinez‐Force, E. (2011). Acyl‐ACP thioesterases from macadamia (Macadamia tetraphylla) nuts: Cloning, characterization and their impact on oil composition. Plant Physiology and Biochemistry, 49(1), 82–87. 10.1016/j.plaphy.2010.10.002 [PubMed] [CrossRef] [Google Scholar]
• Moscetti, R., Frangipane, M. T., Monarca, D., Cecchini, M., & Massantini, R. (2012). Maintaining the quality of unripe, fresh hazelnuts through storage under modified atmospheres. Postharvest Biology and Technology, 65, 33–38. 10.1016/j.postharvbio.2011.10.009 [CrossRef] [Google Scholar]
• Ng, S., Lasekan, O., Muhammad, K., Sulaiman, R., & Hussain, N. (2014). Effect of roasting conditions on color development and Fourier transform infrared spectroscopy (FTIR‐ATR) analysis of Malaysian‐grown tropical almond nuts (Terminalia catappa L.). Chemistry Central Journal, 8, 1–11. 10.1186/s13065-014-0055-2 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
• Niu, Y. X., Rogiewicz, A., Wan, C. Y., Guo, M., Huang, F. H., & Slominski, B. A. (2015). Effect of microwave treatment on the efficacy of expeller pressing of Brassica napus rapeseed and Brassica juncea mustard seeds. Journal of Agricultural and Food Chemistry, 63(12), 3078–3084. 10.1021/jf504872x [PubMed] [CrossRef] [Google Scholar]
• Pankaew, P., Janjai, S., Nilnont, W., Phusampao, C., & Bala, B. K. (2016). Moisture desorption isotherm, diffusivity and finite element simulation of drying of macadamia nut (Macadamia integrifolia). Food and Bioproducts Processing, 100, 16–24. 10.1016/j.fbp.2016.06.007 [CrossRef] [Google Scholar]
• Poogungploy, P., Poomsa‐ad, N., & Wiset, L. (2018). Control of microwave assisted macadamia drying. Journal of Microwave Power and Electromagnetic Energy, 52(1), 60–72. 10.1080/08327823.2017.1421872 [CrossRef] [Google Scholar]
• Schlormann, W., Birringer, M., Bohm, V., Lober, K., Jahreis, G., Lorkowski, S., & Glei, M. (2015). Influence of roasting conditions on health‐related compounds in different nuts. Food Chemistry, 180, 77–85. 10.1016/j.foodchem.2015.02.017 [PubMed] [CrossRef] [Google Scholar]
• Sinanoglou, V. J., Kokkotou, K., Fotakis, C., Strati, I., Proestos, C., & Zoumpoulakis, P. (2014). Monitoring the quality of gamma‐irradiated macadamia nuts based on lipid profile analysis and Chemometrics. Traceability models of irradiated samples. Food Research International, 60, 38–47. 10.1016/j.foodres.2014.01.015 [CrossRef] [Google Scholar]
• Srichamnong, W., & Srzednicki, G. (2015). Internal discoloration of various varieties of Macadamia nuts as influenced by enzymatic browning and Maillard reaction. Scientia Horticulturae, 192, 180–186. 10.1016/j.scienta.2015.06.012 [CrossRef] [Google Scholar]
• Stuetz, W., Schlormann, W., & Glei, M. (2017). B‐vitamins, carotenoids and alpha‐/gamma‐tocopherol in raw and roasted nuts. Food Chemistry, 221, 222–227. 10.1016/j.foodchem.2016.10.065 [PubMed] [CrossRef] [Google Scholar]
• Toth, S. (2017). Comparison of analytical GC‐MS techniques for the determination of volatile and semi‐volatile compounds in raw and roasted Macadamia nuts (Macadamia integrifolia). Abstracts of Papers of the American Chemical Society, 253, 172. [Google Scholar]
• Wall, M. M. (2010). Functional lipid characteristics, oxidative stability, and antioxidant activity of macadamia nut (Macadamia integrifolia) cultivars. Food Chemistry, 121(4), 1103–1108. 10.1016/j.foodchem.2010.01.057 [CrossRef] [Google Scholar]
• Walton, D. A., Randall, B. W., Le Lagadec, M. D., & Wallace, H. M. (2013). Maintaining high moisture content of macadamia nuts‐in‐shell during storage induces brown centres in raw kernels. Journal of the Science of Food and Agriculture, 93(12), 2953–2958. 10.1002/jsfa.6123 [PubMed] [CrossRef] [Google Scholar]
• Walton, D. A., & Wallace, H. M. (2011). Quality changes in macadamia kernel between harvest and farm‐gate. Journal of the Science of Food and Agriculture, 91(3), 480–484. 10.1002/jsfa.4209 [PubMed] [CrossRef] [Google Scholar]
• Wang, Y. Y., Zhang, L., Gao, M. X., Tang, J., & Wang, S. J. (2014). Pilot‐scale radio frequency drying of macadamia nuts: Heating and drying uniformity. Drying Technology, 32(9), 1052–1059. 10.1080/07373937.2014.881848 [CrossRef] [Google Scholar]
• Wang, Y. Y., Zhang, L., Johnson, J., Gao, M. X., Tang, J., Powers, J. R., & Wang, S. J. (2014). Developing hot air‐assisted radio frequency drying for in‐shell macadamia nuts. Food and Bioprocess Technology, 7(1), 278–288. 10.1007/s11947-013-1055-2 [CrossRef] [Google Scholar]
• Xie, Y., Wei, F., Xu, S. L., Wu, B. F., Zheng, C., Lv, X., & Huang, F. H. (2019). Profiling and quantification of lipids in cold‐pressed rapeseed oils based on direct infusion electrospray ionization tandem mass spectrometry. Food Chemistry, 285, 194–203. 10.1016/j.foodchem.2019.01.146 [PubMed] [CrossRef] [Google Scholar]
• Xu, S. L., Wei, F., Xie, Y., Lv, X., Dong, X. Y., & Chen, H. (2018). Research advances based on mass spectrometry for profiling of triacylglycerols in oils and fats and their applications. Electrophoresis, 39(13), 1558–1568. 10.1002/elps.201870102 [PubMed] [CrossRef] [Google Scholar]
• Yoshida, H., Tomiyama, Y., Hirakawa, Y., & Mizushina, Y. (2006). Microwave roasting effects on the oxidative stability of oils and molecular species of triacylglycerols in the kernels of pumpkin (Cucurbita spp.) seeds. Journal of Food Composition and Analysis, 19(4), 330–339. 10.1016/j.jfca.2004.10.004 [CrossRef] [Google Scholar]
• Zhong, Y. J., Xiang, X. Y., Wang, X. H., Zhang, Y., Hu, M. M., Chen, T. T., & Liu, C. M. (2020). Fabrication and characterization of oil‐in‐water emulsions stabilized by macadamia protein isolate/chitosan hydrochloride composite polymers. Food Hydrocolloids, 103, 105655. 10.1016/j.foodhyd.2020.105655 [CrossRef] [Google Scholar]