The influence of amylose and amylopectin on water retention capacity and texture properties of frozen-thawed konjac glucomannan gel

Abstract

As freeze-thaw processing has become an emerging way to regulate the texture properties of the konjac glucomannan (KGM), the freezing-induced syneresis is getting increased concern in the food industry. In this study, the effects of the different types' starches (amylose and amylopectin) and the frozen conditions on the water retention capacity and texture properties of the frozen KGM-Starch blended gel (KS gel) were investigated. Comparing the effects of the subzero conditions and the starches on the blended gel, we found that the latter would be more powerful to affect the syneresis rate and water holding capacity of the frozen KGM gel, and a dense porous network microstructure emerged in the frozen KS gels. Research results also showed that the water holding capacity of the frozen KS gels could be significantly improved for the increased starches content, while their syneresis rate could be lowered significantly (p < 0.05). Besides, the KGM-amylose blended gel showed a greater value of hardness and chewiness than that of the KGM-amylopectin blended gel after being subjected to the same frozen condition. While even though no significant difference in the SR could be observed between the KGM blended gels treated with the different frozen conditions (frozen time, subzero temperature, and the number of freeze-thaw cycles), a noticeable change in their texture properties could still be detected. What's more, results showed that starch types and concentrations would profoundly affect the proportion of water at different states in the KGM blended gels. These results suggest that the frozen-thawed stability of the KGM gel could be improved by adding in the different types of starch, which may provide some guidance for the production of frozen KGM gel food.