Improving Gel Properties of Glucomannan/-carrageenan Blends by Controlling Ethanol pH for Glucomannan Purification

Konjac glucomannan (KGM) is commonly blended with kappa-carrageenan to improve the gel properties of food, which are mostly influenced by KGM purification. Control of ethanol pH for KGM purification is an easy and simple option to modify the properties of KGM, that tends to alter the gel properties of kappa-carrageenan/KGM blends. In this study, the effect of ethanol at different pH (ranging from 2.5 to 12.5) on KGM was investigated, and the gels of kappa-carrageenan with KGM purified by ethanol at different pH were prepared with microwave heating. With KGM purified with ethanol between pH 5.5 and 9.5, kappa-carrageenan/KGM blends exhibited higher gel strength, hardness and water holding capacity than those of gel with native KGM, which was much related with the removal of impurity, the increased viscosity and altered structure of KGM, enhancing the interaction between kappa-carrageenan and KGM. Poor gel properties of the blends were observed with KGM purified with ethanol at pH between 2.5 and 4.5 caused by KGM degradation, or at pH 12.5 due to the removal of acetyl groups. Thus, control of ethanol pH during KGM purification can easily and simply optimize the gel characteristics of kappa-carrageenan/KGM blends to meet desired application requirements.