Characterisation of fiber obtained from pumpkin (Cucumis moschata duch.) mesocarp through enzymatic treatment.

摘要

Cell wall-enriched pumpkin (Cucumis moschata) powder was submitted to enzymic hydrolysis by cellulase or hemicellulase in order to evaluate the performance of these cell wall-degrading enzymes on that substrate. Different enzyme-substrate ratios were evaluated, together with the effect exerted by the buffer on cell wall polysaccharides. Cellulase treatment led to the release of pectin macromolecules which included homogalacturonans side chains, the rhamnogalacturonan I core and rhamnogalacturonan II, in conjunction with xylogalacturonans. The content of galacturonic acid in the product obtained ranged from 545 to 781 g/kg of fibre. Hemicellulases produced intense pectin hydrolysis leading to fibre-fractions with galacturonic acid contents ranging from 390 to 444 g/kg of fibre and enriched in glucose polymers as the enzyme proportion increased; little rhamnogalacturonan-I was present. The acidic citrate buffer (pH 5.2) used to optimize enzyme activity was able per se remove noncovalent cross-links, such as ionic bonds. As a consequence, pectin-in-extensin entanglements, pectins joined by Ca2+-bridges through the homogalacturonan side chains and some pectins originally soluble in cold water due to little or no binding to the cell wall could be removed by this citrate buffer. Enzymic hydrolysis, as well as buffer extraction, produced fibre-products with an important thickening effect in aqueous systems. This effect became smaller as the enzyme-substrate ratio was increased and, in general, the fibre fractions isolated caused an in vitro glucose diffusion retardation.