Mechanism of lowering water activity of konjac glucomannan and its derivatives

Moisture retaining materials are widely used in the food, cosmetic and tobacco industries. Conventional materials, for example, glycerin and propylene glycol have reasonable moisture absorption abilities, but poor moisture retention. Konjac glucomannan (KGM) is a heteropolysaccharide made up of glucose and mannose, linked with β-1,4 glycosidic bonds. Konjac superabsorbent polymer (KSAP) is a derivative containing hydrophilic groups and a network structure prepared by grafting sodium acrylate on to KGM. Previous work has shown that KGM and KSAP have properties which can lower water activity (aw). The objective of this paper is to consider the mechanism of this process. Filter-paper is used as a model fiber instead of tobacco, where this effect is practically important. Moisture absorption and retention of KGM and KSAP are compared with glycerin and propylene glycol. Moisture desorption isotherms have been determined and fitted to the GAB model. The results show that the moisture retention of KGM and KSAP are better than propylene glycol and glycerol. At a given moisture content, aw of filter-paper containing KSAP was the lowest. The monolayer moisture content and net isosteric heat of desorption of filter-paper containing KGM and KSAP were greater than that of the control groups. This study demonstrated that KGM and KSAP have the potential to be used as moisture retaining ingredients.