Effects of konjac glucomannan and freezing on thermal properties, rheology, digestibility and microstructure of starch isolated from wheat dough

Konjac glucomannan (KGM) is used as an additive to improve the properties of frozen wheat-based foods. The effects of KGM concentration (0.5, 1.5, 2.5, 3.5 and 4.5 g/100 g of the wheat starch weight) on the thermal properties, rheology, digestibility and microstructure of frozen wheat starch were investigated in this study. The results revealed that KGM had a positive influence on the water absorption capacity, transparency, thermal stability and viscoelasticity of frozen wheat starch but there was a negative effect on solubility, swelling force and digestibility. Specifically, KGM decreased the crystallinity of frozen wheat starch from 28.57 to 6.47%, implying that KGM could retard the retrogradation of frozen wheat starch. Notably, the network structure of frozen wheat starch with KGM addition was less disruption of surface structure and more adhesions than those of control. Generally, the addition of KGM had positive effects on the thermal properties, rheology and digestibility of frozen wheat starch, which provides a theoretical basis for the application of KGM in the industrial production of frozen wheat-based foods.