Inhibit the intrinsic bacteria from konjac glucomannan hydrosol for its improved viscosity stability

Abstract

The highly viscous konjac glucomannan (KGM) hydrosol is desirable in many food uses, ranging from thickening agent, emulsion stabilizers and baking additives to the nutrient deliveries. However, its drastically dropped viscosity, which occurs after a short period of placement, is a detrimental problem that remains unresolved. Herein, the intrinsic spoilage bacteria from KGM, for the first time, was confirmed as the viscosity reducer. Six major kinds of bacterial strains were found and isolated from the KGM culture medium, which all belonged to the Paenibacillus polymyxa and produced high level of β-mannanase for KGM degradation. More importantly, we noticed that the presence of zinc ion in KGM hydrosol demonstrated surprisingly high efficiency to restrict the thinning behaviors. The ZnSO4 obviously suppressed the growth of bacteria. In addition, Zn2+ can interact with β-mannanase, change its secondary structure, and thus reduce their enzyme activities, as reflected by the isothermal titration calorimetry (ITC) and circular dichroism (CD) test. Our study provides a safe strategy to maintain the viscosity of KGM hydrosol for further food applications.