A metabolomics-based approach for the evaluation of off-tree ripening conditions and different postharvest treatments in mangosteen (Garcinia mangostana) (Flesh parts assay)

INTRODUCTION: Metabolomics is an important tool to support postharvest fruit development and ripening studies. Mangosteen (Garcinia mangostana L.) is a tropical fruit with high market value but has short shelf-life during postharvest handling. Several postharvest technologies have been applied to maintain mangosteen fruit quality during storage. However, there is no study to evaluate the metabolite changes that occur in different harvesting and ripening condition. Additionally, the effect of postharvest treatment using a metabolomics approach has never been studied in mangosteen.OBJECTIVES: The aims of this study were to evaluate the metabolic changes between different harvesting and ripening condition and to evaluate the effect of postharvest treatment in mangosteen.METHODS: Mangosteen ripening stage were collected with several different conditions ('natural on-tree', 'random on-tree' and 'off-tree'). The metabolite changes were investigated for each ripening condition. Additionally, mangosteen fruit was harvested in stage 2 and was treated with several different treatments (storage at low temperature (LT; 12.3 ± 1.4 °C) and stress inducer treatment (methyl jasmonate and salicylic acid) in comparison with control treatment (normal temperature storage) and the metabolite changes were monitored over the course of 10 days after treatment. The metabolome data obtained from gas chromatography coupled with mass spectrometry were analyzed by multivariate analysis, including hierarchical clustering analysis, principal component analysis, and partial to latent squares analysis.RESULTS: 'On-tree' ripening condition showed the progression of ripening process in accordance with the accumulation of some aroma precursor metabolites in the flesh part and pectin breakdown in the peel part. Interestingly, similar trend was found in the 'off-tree' ripening condition although the progression of ripening process observed through color changes occurred much faster compared to 'on-tree' ripening. Additionally, low-temperature treatment is shown as the most effective treatment to prolong mangosteen shelf-life among all postharvest treatments tested in this study compared to control treatment. After postharvest treatment, a total of 71 and 65 metabolites were annotated in peel and flesh part of mangosteen, respectively. Several contributed metabolites (xylose, galactose, galacturonic acid, glucuronate, glycine, and rhamnose) were decreased after treatment in the peel part. However, low-temperature treatment did not show any significant differences compared to a room temperature treatment in the flesh part.CONCLUSIONS: Our findings clearly indicate that there is a similar trend of metabolic changes between on-tree and off-tree ripening conditions. Additionally, postharvest treatment directly or indirectly influences many metabolic processes (cell-wall degrading process, sweet-acidic taste quality) during postharvest treatment.

Flesh parts assay is reported in the current study MTBLS872
Peel parts assay is reported in MTBLS871

引言：代谢组学是支持采后果实发育与成熟研究的重要工具。山竹（Garcinia mangostana L.）是一种经济价值颇高的热带水果，但采后贮藏期极短。目前已有多项采后技术被应用于贮藏过程中维持山竹果实品质，但尚无研究评估不同采收与成熟条件下的代谢物变化。此外，采用代谢组学方法探究采后处理对山竹的影响的相关研究也尚未见报道。
研究目的：本研究旨在评估不同采收与成熟条件下的代谢物变化，并探究采后处理对山竹的影响。
实验方法：本研究收集了三种不同成熟条件下的山竹果实：「树上自然成熟」「树上随机采收」以及「采后离体成熟」，并分析了每种成熟条件下的代谢物变化。此外，选取处于第2成熟阶段的山竹果实，设置不同处理组：低温贮藏组（LT；12.3 ± 1.4 ℃）、胁迫诱导剂处理组（茉莉酸甲酯与水杨酸），并以常温贮藏组作为对照，在处理后10天内监测其代谢物变化。采用气相色谱-质谱联用技术获取代谢组数据，并通过多元统计分析方法进行处理，包括层级聚类分析、主成分分析以及偏最小二乘分析。
实验结果：「树上自然成熟」组的果实成熟进程与果肉中部分香气前体代谢物的积累、果皮果胶降解的趋势相一致。有趣的是，「采后离体成熟」组也呈现出相似的成熟趋势，但通过色泽变化观察到的成熟进程远快于「树上自然成熟」组。此外，相较于本研究中测试的其他采后处理及对照处理，低温贮藏是延长山竹货架期最有效的手段。采后处理后，分别在山竹果皮与果肉中注释得到71种和65种代谢物。果皮中多种关键代谢物（木糖、半乳糖、半乳糖醛酸、葡糖醛酸、甘氨酸及鼠李糖）在处理后含量下降。但在果肉中，低温贮藏与常温处理并未呈现出显著的代谢差异。
研究结论：本研究结果明确表明，树上成熟与采后离体成熟两种条件下的代谢物变化趋势相似。此外，采后处理可直接或间接影响采后贮藏过程中的多项代谢过程，包括细胞壁降解过程、酸甜风味品质调控等。
本研究的果肉代谢组学分析数据收录于MTBLS872，果皮代谢组学分析数据收录于MTBLS871。