Effects of Molar Mass on Water Binding Properties of γ-irradiated Konjac Glucomannan

Abstract

Phase transition behavior of sorbed water in Konjac glucomannan (KM)-water systems with various molar mass was investigated using differential scanning calorimetry (DSC). The measurements were performed repeatedly for 3 cycles. In KM-water systems, non-freezing water (W_nf), four types of freezing bound water (W_fb) and free water (W_f) were identified. The W_fb appeared at increasing water content (Wc) in the order; W_fb1, W_fb2, W_fb2* and W_fb3. The proportion of each type of W_fb changed with increasing Wc. W_fb1, W_fb2, and W_fb2* transferred to W_f in high Wc region, but W_fb3 still kept interaction with KM chains. The same types of sorbed water existed in KM with lower molar mass. The amount of W_nf decreased with decreasing molar mass at high Wc, in particular for KM with molar mass less than 2.0×10⁵ Da. The W_fb in KM matrix with high molar mass is strongly influenced by surrounding KM chains, that is to say the water binding ability decreases with decreasing molar mass.