Prasanna V, Prabha T N, Tharanathan R N
Department of Biochemistry and Nutrition, Central Food Technological Research Institute. Mysore, Karnataka, 570020. India.
Crit Rev Food Sci Nutr. 2007;47(1):1-19. doi: 10.1080/10408390600976841.
Fruits constitute a commercially important and nutritionally indispensable food commodity. Being a part of a balanced diet, fruits play a vital role in human nutrition by supplying the necessary growth regulating factors essential for maintaining normal health. Fruits are widely distributed in nature. One of the limiting factors that influence their economic value is the relatively short ripening period and reduced post-harvest life. Fruit ripening is a highly coordinated, genetically programmed, and an irreversible phenomenon involving a series of physiological, biochemical, and organoleptic changes, that finally leads to the development of a soft edible ripe fruit with desirable quality attributes. Excessive textural softening during ripening leads to adverse effects/spoilage upon storage. Carbohydrates play a major role in the ripening process, by way of depolymerization leading to decreased molecular size with concomitant increase in the levels of ripening inducing specific enzymes, whose target differ from fruit to fruit. The major classes of cell wall polysaccharides that undergo modifications during ripening are starch, pectins, cellulose, and hemicelluloses. Pectins are the common and major components of primary cell wall and middle lamella, contributing to the texture and quality of fruits. Their degradation during ripening seems to be responsible for tissue softening of a number of fruits. Structurally pectins are a diverse group of heteropolysaccharides containing partially methylated D-galacturonic acid residues with side chain appendages of several neutral polysaccharides. The degree of polymerization/esterification and the proportion of neutral sugar residues/side chains are the principal factors contributing to their (micro-) heterogeneity. Pectin degrading enzymes such as polygalacturonase, pectin methyl esterase, lyase, and rhamnogalacturonase are the most implicated in fruit-tissue softening. Recent advances in molecular biology have provided a better understanding of the biochemistry of fruit ripening as well as providing a hand for genetic manipulation of the entire ripening process. It is desirable that significant breakthroughs in such related areas will come forth in the near future, leading to considerable societal benefits.
水果是具有重要商业价值且在营养方面不可或缺的食品。作为均衡饮食的一部分，水果通过提供维持正常健康所需的必要生长调节因子，在人类营养中发挥着至关重要的作用。水果在自然界中分布广泛。影响其经济价值的限制因素之一是相对较短的成熟期和较短的采后寿命。果实成熟是一个高度协调、由基因编程且不可逆转的现象，涉及一系列生理、生化和感官变化，最终导致具有理想品质属性的柔软可食用成熟果实的发育。成熟过程中过度的质地软化会导致储存时产生不良影响/变质。碳水化合物在成熟过程中起着主要作用，通过解聚导致分子大小减小，同时成熟诱导特异性酶的水平增加，其作用靶点因水果而异。在成熟过程中发生修饰的主要细胞壁多糖类包括淀粉、果胶、纤维素和半纤维素。果胶是初生细胞壁和中胶层的常见且主要成分，对水果的质地和品质有贡献。它们在成熟过程中的降解似乎是许多水果组织软化的原因。从结构上讲，果胶是一组多样的杂多糖，含有部分甲基化的D-半乳糖醛酸残基以及几种中性多糖的侧链附属物。聚合度/酯化度以及中性糖残基/侧链的比例是导致其（微观）异质性的主要因素。果胶降解酶如多聚半乳糖醛酸酶、果胶甲酯酶、裂解酶和鼠李糖半乳糖醛酸酶与果实组织软化关系最为密切。分子生物学的最新进展使人们对果实成熟的生物化学有了更好的理解，也为整个成熟过程的基因操作提供了帮助。期望在不久的将来，这些相关领域能取得重大突破，带来可观的社会效益。
