[The role of hydrolytic enzymes in rheological properties of fruits and vegetables]
1999
Vidrih, R. (Ljubljana Univ. (Slovenia). Biotechnical Fac., Food Science and Technology Dept.)
Pectin molecule consists of galacturonic acid included in the cell wall and has an influence on fruit and vegetable texture together with cellulose and hemicellulose. Pectin molecule is degraded during fruit ripening by means of hydrolytic enzymes (endo and ekso polygalacturonase, endo beta (1-4) glucanase and pectin methyl esterase). Hydrolytic enzyme cleavage of pectin or cellulose molecule yields smaller molecules which results in fruit softening. Activity of hydrolytic enzymes depends on fruit maturity, fruit species and storage conditions (temperature, content of CO2, O2 and ethylene). Some tomato mutants show reduced activity of hydrolytic enzymes due to mutations on genes coding for hydrolytic enzymes, or coding for enzymes involved in ethylene synthesis and transduction of ethylene signal. Ethylene or gaseous hormone accelerates ripening and the activity of hydrolytic enzymes. The rate of pectin degradation influences fruit softening and viscosity of juice and some processed fruit and vegetable. Fruit pectin is used to increase the viscosity of some fruit products and as gelation agent in cosmetic products. Presence of pectin molecules in fruit juices disables the precipitation of insoluble solids; addition of polygalacturonase to the turbid juices speed up the precipitation process and makes the filtration much easier. Inoculation of grapes with botritis yields glucanes and other polysacharids causing turibidity, increasing viscosity and making filtration more troubled. Addition of enzymes (glucanases) degrade glucanes and resolve the problems to some degree.
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