Hydration, water distribution and microstructure of gluten during freeze thaw process: Role of a high molecular weight dextran produced by Weissella confusa QS813

The effect of exopolysaccharide (EPS) produced by Weissella confusa QS813 on the hydration, water distribution, rheology and microstructure of wheat gluten during freeze-thaw cycles (FTC) was investigated. Addition of EPS increased the water content of fresh gluten and delayed the dehydration of gluten during FTC. Low field-nuclear magnetic resonance showed that the presence of EPS reduced the mobility of both confined and bulk water in the fresh gluten matrix. Proton distribution changes in gluten during FTC indicated that deterioration of the gluten network was attributable to ice recrystallization of capillary confined water and bulk water. The presence of EPS effectively reduced the release of bulk water and retarded the redistribution of confined water induced by FTC. Dynamic oscillatory studies indicated that the presence of EPS induced a softening effect on the fresh gluten. FTC significantly decreased the rheological parameters, storage modulus (G') and loss modulus (G ''), of all gluten samples. Gluten with higher concentrations of EPS (above 0.5%) exhibited a delayed decrease in G' and G '' and maintained a constant tan delta value after FTC. Laser scanning confocal microscope and scanning electron microscope revealed that EPS maintained the structural integrity of gluten during FTC, suggesting an inhibitory effect on the recrystallization of ice crystals. These results in the present study indicated that the bacterial dextran is a promising cryoprotectant for the frozen dough industry.