Changes in fruit quality during the ripening period and prediction of the optimal harvest time for three Macadamia cultivars in Dehong, Yunnan

【Objective】As an important woody oil crop, macadamia relies heavily on harvest timing for optimal fruit quality. Currently, Yunnan, being China's largest macadamia growing region (accounting for 80% of the national planting area), lacks a scientifically based harvesting decision system, which severely limits the high-quality development of the industry. This study systematically investigated the dynamic changes in the appearance traits and fruit quality of the main macadamia (Macadamia spp.) varieties in Dehong Autonomous Prefecture, Yunnan province, across different harvesting periods in order to provide solution to the problem of unstable fruit quality due to improper harvesting time, thereby es- tablishing scientific harvesting standards. This, in turn, will enhance the commercial value and processing quality of macadamia fruits, thereby contributing to the sustainable development of Yunnan’s macadamia industry.【Methods】Three main cultivars: HAES344, Disi No.1, and Own Choice were selected as test materials for this study. The study was conducted at the Manhuan plantation in Yingjiang County, Dehong Autonomous Prefecture, characterized by a South Asian tropical monsoon climate. During the fruit maturation period (August 1 to October 6), four equally spaced sampling time points were set. Nine healthy 13- year- old trees per variety, totaling 27 sample trees, were used. Fruit cluster samples were collected from four directions in the outer canopy. Appearance indicators such as endocarp color and glossiness were recorded, combining dissection methods with image recording. Fruit morphology parameters including fresh fruit mass, fresh nut mass, and dry mass were measured using an electronic balance with 0.01 g precision. Processing quality indicators such as shelling rate, kernel recovery, and first- grade kernel rate were calculated. Additionally, protein, starch and fat contents were determined. Differences among periods were compared using one-way ANOVA (LSD); Pearson correlation analysis was applied to reveal inter- indicator relationships, and key quality indicators were extracted through principal component analysis. Finally, a multi-dimensional comprehensive evaluation system was constructed using membership function analysis to establish a quantitative prediction model for the harvesting period.【Results】Delaying harvest resulted in gradual endocarp darkening, increased glossiness, and enhanced lignification in all the three varieties. Disi No.1 performed best, displaying deep brown color with bright glossiness at final stage, indicating superior marketability. HAES344 colored slowly, showing uneven deep brown at maturity, while Own Choice maintained lighter pigmentation, reaching only light brown. For processing quality, kernel recovery and grade- one kernel rate significantly increased with delayed harvesting. The kernel recovery of HAES344 increased from 28.35% to 33.67%; that of Disi No.1 from 32.19% to 41.86%, and that of Own Choice from 33.36% to 36.04%. The kernel recovery rate of Disi No.1 peaked at 41.86% during the late harvest period. Own Choice maintained a stable grade-one kernel rate of over 99% in later harvesting stages. Shell-out rate remained stable (variation ≤3%). Nutritionally, fat content was generally high but varied among varieties. The fat content of the three cultivars ranged from 67.90% to 77.82% , with coefficients of variation all below 6% . HAES344 and Own Choice showed an initial increase followed by stabilization, while Disi No.1 first rose, then slowly declined, and finally stabilized. Soluble sugar and protein peaked early then decreased and stabilized. Disi No.1 had the highest soluble sugar content that reached 150 g · kg- 1 soluble sugar, and HAES344 had the highest protein content of 82 g · kg-1 . Moisture content consistently decreased to 18%-20%. Correlation analysis showed fat content positively correlated with kernel recovery and gradeone kernel rates, but negatively correlated with protein, moisture content, and shell-out rate. Principal component analysis indicated the first component (52.0% contribution) reflected fat content and processing quality (HAES344 highest). The second component (26.5% contribution) linked to soluble sugar and shell-out rate (Disi No.1 most prominent). Own Choice showed balanced performance.【Conclusion】 Based on membership function analysis, optimal harvesting periods differed significantly: HAES344 and Own Choice are best harvested in mid-September, while Disi No.1 should be harvested in early October. This finding fills a research gap for macadamia harvesting in Yunnan and provides a scientific basis for precise harvest scheduling. Future studies should incorporate meteorological factors to develop dynamic prediction models for optimizing harvest timing.