Effects of Konjac Glucomannan with Different Molecular Weights on Functional and Structural Properties of κ-carrageenan Composite Gel

In this study, the properties of konjac glucomannan with different molecular weights and their effects on the functional and structural properties of κ-carrageenan (κ-CA) composite gel were analyzed. Native konjac glucomannan (K1: M_{w =} 67,158 g/mol) was hydrolyzed by β-mannanase to obtain three konjac glucomannan with different molecular weights (K2: M_w = 65,124 g/mol, K3: M_w = 32,302 g/mol, and K4: M_w = 17,102 g/mol). The results showed that the hydrolyzed K2, K3, and K4 had lower viscosity, more loose and porous structure, shorter molecular chain and stronger antioxidant activity than native K1. K2 and K3 increased the hardness, gumminess, chewiness, water holding capacity and stronger antioxidant activity but decreased the cohesiveness, resilience, and transparency of κ-CA gel. Hierarchical cluster analysis confirmed that K2/κ-CA and K3/κ-CA gels had good gel properties with better texture and water holding capacity as compared to the other samples, which might be related to their smoother and more compact gel structure and enhanced hydrogen bond. The competition for water molecules between κ-CA and over degraded K4 induced the poor water holding capacity and gel structure for their composite gel. The results revealed the gelation changes of κ-CA composite gel affecting by konjac glucomannan with different molecular weights, and can lay a theoretical foundation for the development and application of their compound food additive.