Pectin Hydrolysis In Vivo and its role in Fruit Softening during Ripening in Mango (Mangifera Indica L)

Prasanna, V. (2002) Pectin Hydrolysis In Vivo and its role in Fruit Softening during Ripening in Mango (Mangifera Indica L). PhD thesis, University of Mysore.

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Abstract

<p align="justify">Mango (Mangifera indica L), the 'King of fruits' is a commercially important fruit crop of tropical world. Despite India being the major producer of mango contributing 54% of the total world production, the fruit economy is far from satisfactory. One of the limiting factors that influence the economic value is the relative short ripening period and post-harvest life. In addition, excessive textural softening during ripening leads to adverse effects upon storage. Thus, delaying ripening-associated changes in this fruit will lead to greater 'commercial value addition' in fruit biotechnology. Textural softening during ripening is of immense importance as it directly dictates the fruit shelf life and post-harvest physiology. Control or modification of fruit texture is the main objective of modern 'Fruit Biotechnology'. During textural softening from unripe to ripe stage (i.e., from 'stony hard' to 'soft' stage), carbohydrates undergo hydrolysis to various extent, resulting in depolymerization and decrease in molecular size of the polymers. It is generally partial hydrolysis of the large size carbohydrate polymers. Sometimes, there may be complete hydrolysis or nearly complete hydrolysis as in the case of starch in mango and banana. In the area of fruit ripening, textural softening of tomato fruits has been fairly well studied. In this case, the expression of a-amino cyclopropane carboxylic acid synthase (ACC synthase) and ethylene forming enzyme (EFE) at ethylene level, and polygalacturonase (PG) and pectin methyl esterase (PME) at post ethylene level, were individually suppressed by antisense RNA. Interestingly, all these culminated in a desired end result. Ethylene suppression resulted in overall control of the ripening process, which was triggered by the exogenous ethylene-boost. Genetic manipulation at the textural level resulted specifically in "improved texture" in the transformed tomatoes, where PG and PME suppression yielded firmer fruits and higher solid content, respectively. Since fruits differ in their biochemical make up, it is to be expected that the enzymic targets also differ from fruit to fruit. There may be other equally important hydrolases, which are crucial in fruit texture and textural softening. This study in mango fruit was taken up to specifically identify the crucial and important hydrolases in connection with pectin metabolism, which was studied at both substrate (pectic polysaccharides) as well as enzyme level (pectin-hydrolyzing enzymes). Some new hydrolases other than PG/PME, hitherto unexplored, were observed in mango fruit, which could serve as important targets for pectin dissolution in vivo. It must be noted that the study here forms the basis for further investigation at the gene level. Identification of crucial substrates and their corresponding enzymes in connection with carbohydrate hydrolysis in vivo is important and useful for providing further insights. The literature reports on mango fruit focus more on post harvest physiology, where most of them deal with biochemical changes during ripening, especially on the organic acid metabolism, fruit flavours, volatiles, overall composition and gross changes in total pectin during ripening. However, the precise nature of the pectic polysaccharides and the pectin- degrading enzymes; their quantitative and qualitative changes during ripening in relation to textural softening have not been studied. The present investigation in mango fruit (Mangifera indica cv. Alphonso) is novel and comprehensive. The aim of this study is to understand the factors contributing to the textural changes in relation to pectin degradation during ripening in mango. The knowledge about the composition, structure and nature of the fruit substrates and enzymes during ripening provides a clear insight into the I physical, physiological and biochemical changes involved in the ripening I process. It is vital to understand (identify define) precisely the enzymes that are involved in textural softening of a fruit and the extent of their contribution towards the same. The profile of carbohydrate polymers of a fruit and the changes they undergo, in terms of abundance as well as molecular weight drop along with the activity profile of the related hydrolases during textural softening, and their action on the endogenous substrates give a direct clue to the involvement of specific enzymic targets in the process. This, information would clearly leads to identification of the gene targets, which may be different in different fruits. The main objectives of this present investigation are 1) To study the pectin degradation in mango during ripening. 2) To characterize the major pectic polysaccharides from mango pulp. 3) To purify and to study the properties of a glycanase (PG) and a glycosidase (β galactosidase). 4) To study their involvement in pectin dissolution in vivo.</p>

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Mango ripening mango pectin hydrolysis textural softening pectin metabolism
Subjects:	600 Technology > 08 Food technology > 24 Fruits > 06 Mango 600 Technology > 08 Food technology > 11 Food Biochemistry
Divisions:	Dept. of Biochemistry
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	27 Jun 2005
Last Modified:	28 Dec 2011 09:24
URI:	http://ir.cftri.res.in/id/eprint/101

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