Effects of pasteurization on bioactive polysaccharide acemannan and cell wall polymers from Aloe barbadensis Miller

Physico-chemical modifications promoted by pasteurization treatments, performed at 65, 75 and 85 C, for 15 and 25 min, on acemannan, the main bioactive polysaccharide from Aloe vera (Aloe barbadensis Miller) parenchyma, and cell wall polymers (CWP) were evaluated. The fresh Aloe samples were characterized by a relatively low content of acemannan (107-139 mg/g dm) probably due to the irrigation system used for its cultivation. Pasteurization seemed to increase the yields in acemannan content. However this effect was probably due to the decrease observed in ethanol-soluble mannose for all treatments. Deacetylation and loss of galactose side-chains might have contributed to the formation of new hydrogen bonds between mannose oligosaccharides and the long chains of acemannan. On the other hand, fresh Aloes exhibited a high content of pectic polysacharides, mainly homogalacturonans, accounting for up to 59% of total CWP. Further, pasteurization also affected the CWP, mainly the pectic moieties, in two different ways. On the one hand, a slight degradation of pectins was observed for samples treated at 65 C which may be due to enzymatic degradation. On the other hand, the marked decrease in the pectic polymers (mainly homogalacturonans), observed for samples treated at 85 degrees C, may be due to their thermal degradation. Compositional and structural modifications on the different polysaccharide types were reflected by the significant changes occurring in the related functional properties, such as swelling (Sw), water retention capacity (WRC), and fat adsorption capacity (FAC). Swelling values were exceptionally high for fresh Aloe samples (over 200 mL water/g alcohol insoluble residue (AIR)), and pasteurized samples exhibited even higher Sw values. WRC and FAC values were also very high and exhibited similar trends; only samples pasteurized at 85 degrees C presented a significant decrease in comparison to the values determined for fresh samples. (C) 2011 Elsevier Ltd. All rights reserved.