Effects of Deacetylated Konjac Glucomannan on the pasting, rheological and retrogradation properties of wheat starch

Abstract

The heat intolerance and retrogradation behavior of native wheat starch (WS) are undesirable for starch-based gel foods, therefore the combinations of WS and hydrocolloids have attracted extensive attentions. The objectives of this study were to investigate the effects of konjac glucomannan (KGM) with different degree of deacetylation (DD) on the pasting, rheological and retrogradation properties of WS. Results showed that deacetyl-konjac glucomannan (DKGM) increased the peak viscosity (PV), trough viscosity (TV) and final viscosity (FV), while decreased the breakdown (BD) values of WS, suggesting the enhancement of the viscosity and thermal stability of WS paste. The raised storage modulus (G′) of WS gels with DKGM1 (DD, 48.23%) demonstrated that the partial removal of acetyl groups from KGM chains effectively promoted the formation of gel network, accompanied by increased elasticity. After storing at 4 °C for 7 days, the hardness of gels increased up 369%, while supplement with DKGM significantly (p < 0.05) decreased the hardness. These data demonstrated that DKGM delayed the process of starch retrogradation, which was further verified by LF-NMR analysis. Besides, the addition of DKGM reduced the retrogradation rate, relative crystallinity and the orderliness of WS-DKGM gels with the prolonging of storage at 4 °C, all validating the hindrance of starch retrogradation by DKGM. Therefore, these data suggested that partial deacetylation of KGM could effectively improve the pasting, rheological characteristics and impede the retrogradation of WS.