Syneresis rate, water distribution, and microstructure of wheat starch gel during freeze-thaw process: Role of a high molecular weight dextran produced by Weissella confusa QS813 from traditional sourdough

Background and objectivesMicrobial exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) can enhance technological properties of frozen goods. In this study, 120 LAB strains isolated from Chinese traditional sourdough were screened for EPS production ability. The effect of the produced EPS on the syneresis rate, water distribution, and microstructure of a wheat starch gel during freeze-thaw cycle (FTC) was investigated using centrifuge methods, low field-nuclear magnetic resonance (LF-NMR), scanning electron microscopy (SEM), and a frozen section-optical microscope technique. FindingsOf all screened isolates, Weissella confusa QS813 was identified and found to produce large amounts (up to 18.9g/L) of high molecular mass, low-branched dextran with 97% -(1,6) linkages in the presence of 5% sucrose at 30 degrees C after 24h of incubation. When added in wheat starch (WS) at different concentrations, the dextran at 1% significantly (p<.05) reduced the syneresis rate among all samples, thus the highest stability during free-thaw cycles. The LF-NMR results showed that the addition of EPS at high concentration to WS appeared to alter the distribution and mobility of water in the starch gel. The microstructure of the wheat starch gel with 1% dextran was denser and more uniform compared to that of the wheat starch without dextran. ConclusionThe dextran produced by W.confusa QS813 significantly improved the freeze-thaw stability of wheat starch gel. Significance and noveltyA novel dextran from W.confusa fermentation was appropriately used as a stabilizer in wheat starch based on frozen dough, thus adding new knowledge and its application potential in the frozen dough and food industry trending with consumers' demand for clean label products.