The Improvement Of Viability Of Lactic Acid Bacteria In Frozen Sourdough

The object of this research was to improve the viability of lactic acid bacteria in frozen sourdough. The research included the growth of Lactobacillus plantruam and Lactobacillus brevis; the improvement of cryopreservation of lactic acid bacteria in frozen starter and frozen suspension with additives; the effect of additives on pH, total titration acidity (TTA) of starter and frozen sourdough; the effect of additives on pH, TTA, specific volume, texture and staling of frozen sourdough bread.Lb. plantruam grew faster than Lb. brevis. The pH of the broth with Lb. plantruam dropped faster. More Lb. brevis could survive freezing- frozen storage than Lb. plantruam. Four additives (glutanthione, fructose, sodium glutamate, and ascorbic acid) were added into the suspension before freezing and frozen- storage. All additives showed a protective effect on cell viability as compared to saline solution, especially after 30 days frozen storage. Glutanthione and sodium glutamate showed a better effect in preserving bacterial viability.The proper proportion of wheat flour and tap water was 100: 125. Mix wheat flour and tap water in plastic box with cap. The fermentation had been done at 30℃. Lactobacillus can absorb maltose, and then release fructose and glucose, which can be used by yeast. In this reaserch, the frozen sourdough was fermented by lactic acid bacteria and yeast. The yeast was added at the beginning of sourdough mixing.The response surface analysis methodology of three levels and three factors was introduced to determine the viability of lactic acid bacteria in frozen sourdough. And the influence of starter fermentation time, sourdough frozen period, the amount of additives on starter and sourdough was determined. The acidification ability of the frozen sourdough after thawing, which made of starter with fermentation time longer than 27h, did not change much. After thawing, theΔTTA andΔpH of frozen sourdough with MSG was up to 0.19% and 0.19 respectively, and theΔTTA andΔpH of frozen sourdough with GSH was up to 0.18% and 0.25 respectively.The response surface analysis methodology of three levels and three factors was used to determine the specific volume, hardness and springiness of frozen sourdough bread. And the influence of starter fermentation time, sourdough frozen period, the amount of additives on frozen sourdough texture was determined by texture analyser. Compared to the control samples, MSG and GSH increase the texture of frozen sourdough bread. The influence of frozen sourdough bread storage time, sourdough frozen period, the amount of additives on frozen sourdough bread staling was also determined. After thawing, the hardness and the decrease of hardeness of frozen sourdough bread with MSG was down to 388g and 100g respectively, and the hardness and the decrease of hardeness of frozen sourdough bread with GSH was down to 410g and 100g respectively.