Effects of heat treatment and dehydration on bioactive polysaccharide acemannan and cell wall polymers from Aloe barbadensis Miller

Physico-chemical modifications promoted by heat treatment and dehydration at different temperatures (30-80 degreesC) on acemannan, a bioactive polysacharide from aloe vera (Aloe barbadensis Miller) parenchyma, were evaluated. Modification of acemannan, a storage polysaccharide, was particularly significant when dehydration was performed above 60 degreesC. Heating promoted marked changes in the average molecular weight (MW) of the bioactive polysaccharide, increasing from 45 kDa, in fresh aloe, to 75 and 81 kDa, for samples dehydrated at 70 and 80 degreesC, respectively. This could be attributed to structural modifications, such as deacetylation and losses of galactose-rich side-chains from the mannose backbones These structural modifications were reflected by the significant changes occurring in the related functional properties, such as swelling, water retention capacity, and fat adsorption capacity, which exhibited a significant decrease as the temperature of dehydration increased. Further, dehydration also promoted significant modification of the main type of cell wall polysaccharides present within the aloe parenchyma tissues. Pectic polysaccharides from the cell wall matrix were affected by heating, probably due to either beta-elimination processes or enzyme-catalysed degradation. The influence that these physico-chemical modifications might have on the bioactivity and properties of processed products from A. barbadensis Miller needs to be considered. (C) 2003 Elsevier Science Ltd. All rights reserved.