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Ethephon is a plant growth regulator that triggers diverse responses in plants, such as fruit ripening, leaf senescence, hull senescence, stem elongation, and nut abscission. This study examined how the preharvest application of ethephon 480 SL® affects selected biochemical components and polyphenol oxidase (PPO) activity in two macadamia nut cultivars: '788' and 'Beaumont'. Ethephon was applied to the trees via a Cima mist blower at rates of 13.33 mL/L per hectare for the '788' cultivar and 16.67 mL/L per hectare for the 'Beaumont'. Following harvest, the nuts were stored at 25 °C for 72 days, and samples were taken at 18-day intervals. Standard procedures were used to assess the following: total phenolics, total flavonoids, 2,2,-diphenyl-1-picrylhydrazyl (DPPH) assay, Ferric reducing ability power (FRAP) assay, sucrose, total protein, and PPO activities. This evaluation was carried out across a total of four treatments: ethephon-treated nuts from the orchard floor (ED), ethephon-treated nuts from the tree (ET), untreated nuts from the orchard floor (CD), and untreated nuts from the tree (CT). The evaluation's outcomes were analyzed using a principal component analysis (PCA), a correlation matrix heat map (CMHM), and a graphical assessment. The results unveiled significant correlations and associations among the assessed parameters. The correlation matrix heat map analysis highlighted a strong positive correlation (0.97) between the sucrose and the PPO activity in the 'Beaumont' cultivar, supported by the PCA analysis identifying the ED treatment as the most influential. At the storage period's conclusion, the ED treatment had the highest sucrose content (18.63 mg/g) and polyphenol oxidase activity (1.06 U g−1). In the '788' cultivar, a close relationship emerged between the phenolic content, the PPO activity, and the Ferric reducing antioxidant power (FRAP)'s antioxidant activity. Consistently, the CT treatment (untreated nuts) demonstrated positive correlations with several key parameters in both cultivars, displaying heightened phenolic content and antioxidant activities. Consequently, our findings indicate that the CT treatment, involving tree-harvested nuts without ethephon application, could be the preferred option for sustaining macadamia nuts' quality and shelf life compared to other methods. Moreover, our study underscores the significance of proper storage conditions for maintaining the desired biochemical parameters of macadamia nuts. By comprehending the effects of distinct treatments and harvesting techniques, producers and processors can devise strategies to optimize storage conditions and uphold macadamia nut quality. [ABSTRACT FROM AUTHOR]

The use of ethephon, designed to stimulate nut detachment, initiates the release of ethylene, a well-established regulator of postharvest shelf-life in various agricultural products. This study aimed to assess the impact of ethephon application on individual fatty acids and dietary indicators in two macadamia nut cultivars, namely '788' and 'Beaumont,' during postharvest storage. Nuts that naturally abscised and those detached through ethephon treatment were divided into two groups: the ethylene-treated group (ED) and the control group (CD). Nuts were stored at 25 °C and sampled at 0, 36, and 72 days for fatty profile analysis. Our findings indicated a significant increase in stearic acid content in ED nuts (24,622 µg/g) compared to CD nuts (16,764 µg/g) at the end of the storage period for the 'Beaumont' cultivar. Additionally, unsaturated fatty acids (USFAs), such as eicosatrienoic acid + erucic acid (C20:3n3 + C22:1) and eicosatrienoic acid + alpha-linolenic acid (C20:1 + C18:3n3), were notably reduced. Hierarchical clustering analysis revealed positive correlations between ethylene treatment and saturated fatty acids (SFAs) in both 'Beaumont' (0.78) and '788' (0.80) cultivars. This also coincided with an increase in atherogenic indices, thrombogenic index, and saturation index and a decrease in the hypocholesterolemic/hypercholesterolemic ratio and arachidonic acid (C20:4n6) within the ED group of the 'Beaumont' cultivar, collectively potentially impacting nutritional quality negatively. Furthermore, our findings indicated that the PUFA:SFA ratio was higher in CD (0.51) compared to ED (0.45) on day 72 for the 'Beaumont' cultivar, revealing differences in fatty acid compositions between the two treatment groups. Conversely, for '788', both ED and CD had a PUFA:SFA ratio below 0.45, indicating an increased risk of cardiovascular diseases. These results suggest that ethephon treatment increases SFA levels and reduces USFA levels in the 'Beaumont' cultivar, while the response to ethylene varies between the two cultivars. Thus, the study provides insight into the significant role of modifying ethephon treatment methods and careful cultivar selection in the attainment of optimal nutritional value and shelf-life of macadamia nuts. [ABSTRACT FROM AUTHOR]

Depending on the temperature regime used during roasting, the biochemical and sensory characteristics of macadamia nuts can change. 'A4′ and 'Beaumont' were used as model cultivars to examine how roasting temperatures affected the chemical and sensory quality of macadamia nuts. Using a hot air oven dryer, macadamia kernels were roasted at 50, 75, 100, 125, and 150 °C for 15 min. The quantity of phenols, flavonoids, and antioxidants in kernels roasted at 50, 75, and 100 °C was significant (p < 0.001); however, these kernels also had high levels of moisture content, oxidation-sensitive unsaturated fatty acids (UFAs), and peroxide value (PV), and poor sensory quality. Low moisture content, flavonoids, phenols, antioxidants, fatty acid (FA) compositions, high PV, and poor sensory quality—i.e., excessive browning, an exceptionally crunchy texture, and a bitter flavor—were all characteristics of kernels roasted at 150 °C. With a perfect crispy texture, a rich brown color, and a strong nutty flavor, kernels roasted at 125 °C had lower PV; higher oxidation-resistant UFA compositions; considerable concentrations of flavonoids, phenols, and antioxidants; and good sensory quality. Therefore, 'A4′ and 'Beaumont' kernels could be roasted at 125 °C for use in the industry to improve kernel quality and palatability. [ABSTRACT FROM AUTHOR]

• Roasted macadamia kernels had high concentration antioxidants, and unsaturated fatty acids. • Roasted nuts displayed low levels of polyphenol oxidase (PPO), peroxide value (PV). • Strong correlations were observesd between ratio of PUFA:MUFA and sensory quality. • Roasting can alter fatty acid profile of the nuts depending on the roasing temperature. Raw and roasted kernels of 'A4' and 'Beaumont' macadamia cultivars were assessed for biochemical and sensory quality during the accelerated storage of 70 days. Kernels were roasted at 125 °C for 15 min using a hot air oven dryer. Roasted kernels had significantly (p < 0.001) high concentration of phenols, antioxidants and good sensory properties: aroma, taste and overall appearance, validated by low levels of polyphenol oxidase (PPO), peroxide value (PV) and fatty acids (FAs) at the end of storage. Whereas, raw kernels had high and unacceptable levels of PPO, PV and FA compositions which accelerated the rancidification process, supported by low concentration of phenols, antioxidants and poor aroma. A strong correlations were observesd between ratio of polyunsaturated FA: monounsaturated FA (PUFA:MUFA) and sensory quality attributes (aroma and appearance) for roasted cultivars before storage. And also positive correlation was observed among PV, rancidity and cultivars which indicate that raw 'Beaumont' and roasted 'A4' macadamia nuts after 70 days of storage had higher PV values, resulting to rancidity taste. Roasting can alter fatty acid profile of the nuts depending on the roasing temperature. These findings demonstrate that roasting can improve macadamia nuts' quality as compared to raw nuts, but the roasting temperature regime needs to be determined for different cultivars. [ABSTRACT FROM AUTHOR]