Research progress in flesh texture and aroma of pears

Abstract: 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.