Research progress on fruit astringency

Abstract:With the improvement of living standards, people have more demands on fruit quality and thestudies on the improvement of fruit interior quality are increasing. Fruit flavor is the major factor impact-ing fruit internal quality and has received more attention by scholars. The formation of fruit quality and itsregulatory aspects has always been a hot research field. The changes of fruit flavor substance are impor-tant indexes to evaluate fruit quality. However, previous researches have placed greater attentions on thesour and sweet aroma of fruit and so on, and the study on the astringencies of fruit is relatively small.There is a lack of a systemic report on the formation and regulation of fruit acerbity. The main reason in-ducing fruit astringency is the existence of polyphenols, which include tannin, catechin, epicatechin, gal-lic acid and so on. Polyphenol contents are closely related to the astringency intensity of fruits. In particu-lar, tannin is the most general and most important substance in the fruit. What's more, the researchershave paid high attention to the biosynthesis pathways of astringent substances and their regulatory mecha-nisms, and a large amount of related research results have been acquired. The previous researches de-scribe the astringency substances inducing fruit acerbity and give a detailed description on the conceptand chemical structure of tannin, astringency of tannin and tannin cells. The results show that the astrin-gency intensity of fruit has no linear relationship with tannin content and correlates well with the structureand different kinds of tannin. There are obvious differences between different levels of fruit astringency involume, amount, density, shape and the development process of tannin cells. This article describes the bio-synthesis pathways of astringent substances, which include the phenylpropanoid pathway and the flavo-noids metabolic pathways. The methods of the regulation on fruit astringency are discussed from three as-pects: physical regulation, chemical regulation, and molecular regulation. These regulation methods canaffect the astringency intensity of fruits through regulating the activity and expression quantity of relatedenzymes. The methods of physical regulation can regulate fruit stringency by certain environmental aspects such as light, temperature and water. The methods of chemical regulation can regulate fruit stringen-cy with plant growth regulation and mineral elements. The methods of molecular regulation are mainlythrough three transcription factors including the MYB transcription factor, b HLH transcription factor, andWD40 transcription factor. Summarizing the results of previous researches, the mechanisms of deastrin-gency primarily include four modes, which are the theory of tannins condensed, the theory of competition,change from soluble tannin to insoluble complex and the dilution effect of tannin cells. The technologiesof fruit deastringency are briefly introduced in this paper, which include the technologies of ethanoldeastringency and carbon dioxide deastringency, and so on. The effects of removing astringency are different with the fruit varieties and growth stages. According to the research achievements that predecessorshave obtained, we propose some advice on future research direction.(1) It is important to strengthen the re-search of the biosynthesis pathway of astringent substances by using molecular biological technology. Youshould clear the biosynthesis pathway of the tannin and perfect the formation mechanism of the fruit acer-bity.(2) Referring to transcription factors found in grapes and persimmons, researchers should carry outthe study on gene discovery and gene mapping of fruit astringency in other types of fruits. It is beneficialto develop the studies on functional identification and regulatory mechanisms of the transcription factorsfor fruit astringency.(3) It is necessary to strengthen the study on the genetic laws of astringency by usingmolecular markers.(4) Except for focusing on the study of deastringenting for persimmons and postharvestfruits, it is necessary to develop the technologies of removing puckery from the various fruit species andexplore the deastringent technology for preharvest fruits when perfecting the technical system of removingpuckery for persimmons, which will provide technical support for improving the fruit quality. From theabove, we can make a review based on the domestic and foreign research reports in this paper, which in-cludes the astringent substances of fruits, the biosynthesis pathways of astringent substances, the modes ofastringency regulation and the mechanisms and methods of deastringenting fruits, we can also come upwith some advice about the research of fruit astringency, includin making a reference for reducing the astringency intensity and improving the fruit quality in the future.