Degradation of water-soluble fibre polysaccharides in carrots after different types of processing

Abstract

The molecular weight distribution and the viscosity of water-soluble polysaccharides isolated from carrots were investigated after different types of heat-treatment, commonly used when preparing food. The materials studied were blanched, boiled, microwaved and canned. Freezing, without any heat-treatment, was used as a reference process. The water soluble polysaccharides were isolated using two different procedures, i.e. before and after enzymic digestion of protein and starch. Only minor differences in molecular weight distribution between frozen and blanched materials could be detected by gel-filtration. However, when the carrots were further heat-treated, i.e. boiled, microwaved and canned, there was an increase in both the high molecular and the low molecular weight fractions of soluble polysaccharides (especially pectic substances) isolated after digestion of protein and starch. This indicated a solubilization of originally isoluble material, as well as a degradation of the soluble high molecular weight material. On the other hand, in the polysaccharide fraction isolated directly, i.e. without any degradation of protein and starch, there was an increase only in the low molecular weight fraction and only when the materials were microwaved and canned. The viscosity of polysaccharides isolated without degradation of protein and starch could be correlated with the extent of degradation of the polysaccharides, and thus also with the degree of heat-treatment, in the following order: freezing, blanching, boiling, and canning. However, the viscosity of soluble fibre isolated after degradation of protein and starch was similar and low for all materials studied.