Cryogelation phenomena in mixed skim milk powder – barley β-glucan–polyol aqueous dispersions

The effects of polyols (fructose, glucose, sorbitol, sucrose and xylose) on cryostructurization of barley mixed-linkage (1 → 3), (1 → 4) β-d-glucans (β-glucans) in the presence of skim milk proteins were investigated; three β-glucan isolates differing in molecular size (apparent molecular weight of 210, 140 and 70 × 103 Da) were used. Polyols were incorporated at 15% (w/w) concentration into aqueous β-glucan (3% w/w)–skim milk (12% w/w) dispersions and the mixed dispersions were subjected to 14 repeated freezing (−15 °C for 24 h) and thawing (5 °C for 24 h) cycles; all preparations gave compact, opaque gels. For the high molecular weight (210 × 103) preparation, with exception of sorbitol, the addition of polyols to β-glucan-skim milk dispersions retarded the cryostructurization, as shown by phenomenological observations after each freezing–thawing cycle and resulted in weaker cryostructurates compared to those of control (polyol-free gels), as determined by small deformation mechanical measurements. Xylose and fructose showed a stronger inhibitory effect on structure formation compared to sucrose and glucose, whereas sorbitol appeared as a network promoting co-solute. However, the above effects of polyols were largely diminished with decreasing of the β-glucan molecular weight and seemed to be independent on the type of polyol for the 140 and 70 × 103 β-glucan samples. Despite the fact that molecular weight of β-glucans can have an impact on the effect of individual polyol on thermostability of cryogels, generally it seems that the melting temperature (Tm) of β-glucan-skim milk cryostructurates, as determined by dynamic rheometry, followed the order sorbitol > sucrose > control, glucose > fructose > xylose. On the other hand, large deformation mechanical tests (compression mode) revealed an increase in firmness and a decrease in brittleness of β-glucan–skim milk cryogels with inclusion of polyols in the order of: sorbitol < sucrose, xylose < fructose, glucose.