Effect of different β-glucans on the gelatinisation and retrogradation of rice starch

Four beta-glucan preparations, i.e., curdlan (CL), oat (OG), barley (BG) and yeast (YG) beta-glucans, were compared for their effects on the gelatinisation and retrogradation of rice starch (RS). Rapid visco-analysis (RVA) showed that addition of any of these beta-glucans significantly increased the peak, breakdown, final, and setback viscosities of RS, whereas the pasting temperatures were significantly decreased by OG or CL addition, but were unaffected by BG or YG addition. Differential scanning calorimetry (DSC) demonstrated that all the beta-glucans had a negligible effect on the onset (T-o), peak (T-p) and conclusion (T-c) temperatures but slightly decreased the gelatinisation enthalpy (Delta H-1) of RS. Storage of all the gels at 4 degrees C resulted in a marked decrease in the T-o, T-p, T-c, and melting enthalpy (Delta H-2) values. The retrogradation ratio (Delta H-2/AH(1)) and the phase transition temperature range (T-c-T-o) of all the gels increased with storage time. Dynamic viscoelastic measurements revealed weak get-like behaviour of all the gels, in which their storage modulus (G') increased and their loss tangent (tan delta) decreased during storage. Steady flow tests illustrated time-dependent shear-thinning (thixotropic) behaviour of all the gels. The hysteresis loop area and the gel hardness increased with storage time. However, the rate and extent of retrogradation and the theological and textural changes of the RS gels were reduced by addition of any of these beta-glucans. The extent of the aforementioned effects differed among the different beta-glucan preparations, generally in the order OG approximate to BG > CL approximate to YG. (C) 2008 Elsevier Ltd. All rights reserved.