Aroma is an important sensory factor in evaluating the quality of pear fruits. This study used headspace solid-phase microextraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC-MS) to analyze the volatile organic compounds (VOCs) of three crispy pears and five soft pears during shelf life, and the changes in soluble solids content (SSC) were analyzed. The results showed that the SSC of the soft pears such as Nanguoli, Jingbaili and Louis was always higher than that of the crispy pears throughout shelf life. A total of 160 VOCs were detected in the eight pear varieties. Orthogonal partial least squares discriminant analysis (OPLS-DA) and hierarchical cluster analysis (HCA) combined with predictor variable importance projection (VIP) showed that the eight pear varieties could be obviously classified into six groups according to the differences in their VOCs, and 31 differential VOCs were screened out, which could be used to differentiate between pears with different flesh textures. The results of clustering heat map analysis showed that, with the extension of shelf life, the content of each different VOC did not change much in crispy pears, whereas the difference in soft pears was larger. This study confirmed the potential of determining the optimal shelf life of different pear varieties about aroma evaluation and studying the mechanism of differences in VOCs in the future.

[目的]探究7个梨品种在不同采收期、不同货架期果肉质地的变化规律及质构性状的差异.[方法]以脆肉梨品种怀来大鸭梨、库尔勒香梨和鸭梨,以及软肉梨品种京白梨、南果梨、五九香和珍妮阿这7个梨品种为试验材料,对不同成熟度梨果的平均单果质量、可溶性固形物含量进行测量,应用质构仪质地多面分析法(TPA)测定果肉的破裂力、硬度、内聚性、弹性、胶黏性和咀嚼性等6个质地参数指标,并对质地参数进行相关性分析.[结果]7个梨品种的平均单果质量均随着成熟度的增加而逐渐升高,可溶性固形物含量的变化趋势因品种和果肉质地类型的不同而存在差异.不同采收期的脆肉梨怀来大鸭梨、库尔勒香梨和鸭梨,随着货架期的延长,果肉破裂力、硬度、内聚性、弹性、胶黏性和咀嚼性均在较小的范围内变化,且随着采收期的延长呈逐渐降低的趋势,其中鸭梨的果肉质地参数值始终处于较高水平.而软肉梨京白梨、南果梨、五九香和珍妮阿果肉质地参数的变化与脆肉梨相比较大,果肉破裂力、硬度、弹性、胶黏性和咀嚼性等参数值均在货架期7～14 d时呈下降趋势,在货架期14～21 d时无明显变化,内聚性的变化趋势因品种不同而存在差异.相关性分析表明,果肉破裂力、硬度、弹性、胶黏性和咀嚼性之间均呈极显著正相关,而内聚性与硬度和咀嚼性呈显著正相关,与胶黏性呈极显著正相关.[结论]采用质构仪TPA法获得的相关质地参数指标能准确地反映出不同成熟度的梨果在货架期质地的变化规律及不同梨品种之间质构特性的差异,为梨果实采收期判断和采后果肉质地鉴定评价提供一定的参考依据.

Pears are popular by consumers because of their unique taste and flavor. Flesh texture and aroma are important economic characteristics of pear fruits. There are many reports on the research of flesh texture and aroma of pears, and more research progress had been made. First of all, the results of research on flesh texture and aroma of pears are summarized in this paper. According to the flesh texture, pear germplasm resources can be divided into melting-flesh type, crisp-flesh type and interspecific hybrid type. Among them, Pyrus bretschneideri, P. pyrifolia and P. sinkangensis are planted and cultivated as crisp-flesh pear fruits, which are crisp and juicy, with good eating quality, while P. communis and P. ussuriensis were melting-flesh pear fruits, which could be eaten only after ripening and softening. The flesh texture of fruit is often directly used to reflect the taste of the fruit, and aroma is an important factor affecting the sensory quality of the fruit. The volatile substances in pear fruit mainly include esters, alcohols, alkenes, ketones and acids. The type and content of these volatile compounds determine the flavor of the fruit and consumer preferences. Secondly, the mechanism of flesh texture and aroma formation of melting-flesh pear and crisp-flesh pear are elaborated. The degradation pathway of pectin in the softening process of melting-flesh pear and crisp-flesh pear is significantly different, which leads to the different ripening and softening characteristics between two types of pear varieties. When the contents of water-soluble polyuronides（WSP） and ionic-soluble polyuronides（ISP） in melting-flesh pear fruits increase and the contents of CDTA-soluble polyuronides（CSP） decrease, the flesh hardness decreases; However, the content of WSP in crisp-flesh pear fruit increases slowly, the content of CSP is higher and decreases slightly with the extension of storage time, and the flesh hardness decreases slowly. In addition, sucrose metabolism is also involved in the ripening and softening of melting-flesh pears,which could be regulated by regulating the composition and content of soluble sugar. LAC gene family plays an important role in the lignin synthesis and stone cell development of Dangshansuli, which affects the fruit hardness. The aroma reflects the flavor characteristics of different pear varieties. It could affect the synthesis of aroma substances in melting-flesh pear fruits by regulating the expression of genes related to ester synthesis and the differential expression of plant hormone signal transduction genes and genes encoding transcription factors. In crisp-flesh pears, LOX gene family is involved in the synthesis of aldehydes and alcohols in the fruit. BAHD acyltransferase superfamily catalyzes the synthesis of esters, terpenes and other substances, The ADH gene family is closely related to the formation of alcohols during fruit ripening. Furthermore, the factors affecting the flesh texture and aroma formation are reviewed. The flesh texture and aroma substances in the fruit of pear are different due to different varieties, maturity and post-harvest treatment methods. There are significant differences in flesh hardness,brittleness, stickiness, chewiness and other texture parameters among different pear varieties’ fruits.The hardness and breaking force of most soft flesh pears decrease rapidly with the extension of storage time, while the hardness and breaking force of most crisp flesh pears cannot change much with the extension of storage time. There are also great differences in the types and contents of aroma substances and the types of characteristic aroma substances among different pear varieties’ fruits. Therefore, different pear varieties’ fruits show different flavor type. The maturity of harvest also affects the flesh texture of pear fruit and the type and content of aroma substances in the fruit. Properly harvested pear fruits could show good fruit texture and quality, while delayed harvest fruits with higher maturity could lead to texture softening and short shelf life. But compared with the fruits harvested early, the fruits harvested late show more fragrant flavor, and the fruits harvested early have a green flavor. Postharvest 1-MCP treatment for pear fruits could significantly inhibit the deterioration and softening of the fruit, maintain the quality of the fruit during storage, but lead to the reduction of the type and concentration of volatile substances in the fruit. The loss of fruit flavor could be reduced and the quality of the fruit could be maintained by increasing the temperature during storage or applying ethylene, salicylic acid, glycine betaine and other exogenous regulators before storage. In addition, the flesh quality of pear fruits is affected by the different storage methods and storage time. And the types and relative content of aroma substances are affected by bagging, fertilization and other treatments during development of pear fruits. Finally, the study directions in flesh texture and aroma is suggested, in order to provide reference for the study of evaluation on flesh texture, fruit aroma and the cultivation of new pear germplasm with different aroma types.