不同类型桃果实内酯芳香物质构成与重要性评价

【目的】分析不同类型成熟桃果实的内酯芳香物质构成,并评价其对于桃果实芳香的重要性。【方法】以涵盖不同果肉质地、果肉颜色、果实成熟期等的多品种桃果实为试材,采用顶空固相微萃取-气相色谱质谱联用体系检测样品的芳香物质,通过精确的定性和定量分析,明确内酯芳香物质的构成,并结合芳香物质的气味活性值分析评价其重要性。【结果】内酯芳香物质存在于本研究全部桃品种的成熟果实中,样品中共检测到10种内酯芳香物质,包括γ-己内酯、γ-辛内酯、γ-庚内酯、γ-癸内酯、5-羟基-2, 4-癸二烯酸-δ-内酯、δ-癸内酯、γ-十一内酯、δ-辛内酯、茉莉内酯、顺式-4-羟基-6-十二烯酸内酯。各内酯物质具有特定的气味属性,主要散发果香（桃/椰子）、甜香、奶油香、焦糖香、花香和草本味等气味。不同品种的桃果实共有的内酯物质是γ-己内酯,较为普遍存在的内酯物质包括γ-癸内酯和δ-癸内酯,部分品种存在特有的内酯物质,如‘深州蜜桃’果实中的顺式-4-羟基-6-十二烯酸内酯。果实成熟期时,溶质‘白花水蜜’‘深州蜜桃’‘橙香’‘奉化玉露（晚）’‘肥城红里大桃’等品种中检测到较多种类的内酯芳香物质,硬质‘霞脆’‘秦王’‘华玉’等品种果实具有较少种类的内酯芳香物质。气味活性值分析表明,由于极低的气味阈值和较高的物质含量,γ-癸内酯存在于大部分品种中,且对于这些品种桃香气的形成具有重要贡献,使溶质‘深州蜜桃’‘橙香’‘奉化玉露（晚）’‘白花水蜜’等品种果实均具有较为强烈的典型的桃香气味,溶质‘阿初桃’和硬质‘华玉’品种的典型桃果芳香较淡,而未检测到该内酯的硬质‘秦王’‘霞脆’品种果实则没有典型的桃果芳香。此外,γ-辛内酯使部分品种（本研究中为‘橙香’和‘深州蜜桃’）桃果实呈现更为强烈的椰果味和非常甜的气味。【结论】内酯是桃果实挥发性芳香物质的一个重要类别,桃果实内酯物质构成丰富,成熟果实至少包含10种内酯芳香物质。内酯物质类别和含量的差异是不同品种尤其是不同果肉质地的桃果实芳香特征的一个重要体现,而不同果肉颜色或成熟期品种的内酯芳香无显著差异。γ-己内酯是品种之间共有的内酯物质,γ-癸内酯和δ-癸内酯是品种之间较为普遍存在的内酯,顺式-4-羟基-6-十二烯酸内酯等是部分品种特有的内酯物质。γ-癸内酯和γ-辛内酯等内酯对于品种的典型桃香气以及独特芳香气味的形成具有重要贡献。

Characterization of the Lactone Volatile Compounds in Different Types of Peach (Prunus persica L.) Fruit and Evaluations of Their Contributions to Fruit Overall Aroma

【Objective】 The objective of this study was to conduct a systematical analysis of the lactone volatile compounds in different types of ripe peach fruit (Prunus persica L.) and to evaluate the contributions of each lactone compound to peach fruit aroma. 【Method】 Multiple peach cultivars with different flesh textures, flesh colors and fruit growth periods were used in this study. The gas chromatography-mass spectrometry system was employed to identify and quantify the lactone volatile compounds in peach fruit, and the odor activity value was used to evaluate the contributions of each lactone compound to the fruit aroma of respective cultivars. 【Result】 Lactone volatile compounds were detected in ripe fruit of all peach cultivars, and a total of ten lactone volatile compounds were identified in peach fruit, including γ-hexalactone, γ-octalactone, γ-heptalactone, γ-decalactone, δ-deca-2, 4-dienolactone, δ-decalactone, γ-undecalactone, δ-octalactone, jasmine lactone, and cis-4-hydroxydodec-6-enoic acid lactone. Each lactone compound was of specific odor notes, and the lactone compounds predominantly emit fruity (reminiscent of coconut and peach), sweet, dairy, caramel, floral, and herbaceous smells. The common lactone compound shared by all cultivars was γ-hexalactone, the frequently detected lactone compounds were γ-decalactone and δ-decalactone, and some lactone compounds were specific to individual cultivars, such as cis-4-hydroxydodec-6-enoic acid lactone in Shenzhoumitao. Relatively higher numbers of lactone volatile compounds were detected in ripe fruit of melting peach cultivars, including Baihuashuimi, Shenzhoumitao, Chengxiang, Fenghuayulu (wan), and Feichenghonglidatao, while the lower numbers of lactone volatile compounds were present in stony hard peach cultivars including Xiacui, Qinwang and Huayu. The analysis of the odor activity values of the lactone volatile compounds revealed the universal contribution of γ-decalactone to the aroma of the majority of cultivars due to its low odor threshold value and high concentrations in fruit. γ-Decalactone conferred the strong characteristic peach-like odor to melting peach cultivars, including Shenzhoumitao, Chengxiang, Fenghuayulu (wan), and Baihuashuimi, while plain peach-like odor was observed in melting peach Achutao and stony hard peach Huayu due to the lower odor activity values of γ-decalactone, and the characteristic peach-like odor note was absent in stony hard peach Qinwang and Xiacui fruit as no γ-decalactone was detected. Besides, γ-octalactone contributed to the coconut and very sweet odors of specific cultivars, such as Chengxiang and Shenzhoumitao. 【Conclusion】 Lactones constituted an essential chemical group of the volatile compounds of peach fruit, and the mature peach fruit presented at least ten lactone volatile compounds. Various lactone volatile compounds and their different concentrations showed the aroma characteristics of different types of peach cultivars, especially the cultivars of different flesh textures, while not the ones of different flesh colors or fruit growth periods. γ-Hexalactone was the common lactone shared by all cultivars, γ-decalactone and δ-decalactone were frequently detected lactone compounds, and cis-4-hydroxydodec-6-enoic acid lactone and other lactones were specific to individual cultivars. γ-Decalactone, γ-octalactone and other lactones made important contributions to the characteristic peach-like odor and other unique odor notes in different peach cultivars.