Red Bean Sourdough Fermented By Lactic Acid Bacteria And Its Mechanism Studies On Improving Frozen Dough Baking Properties

Frozen dough technology is essential for the industrialization of bakery products.Problems such as higher production cost,shorter shelf life and unstable product quality of bakery products could be effectively solved by frozen dough technology.However,during frozen storage of dough,wheat gluten is depolymerized which results in the deterioration of the quality of frozen dough.Search for solutions to the deteriorated dough quality during frozen storage has gained a lot of interest in modern baking science and technology research.Sourdough fermentation technology has been used in the baking field for a long time.Sourdough has been applied as a natural biological improver to modify the texture,nutrition and flavor of bakery products.However,few known studies have applied sourdough in frozen legume dough systems.In this article,exopolysaccharide(EPS)-producing strain Weissella confusa QS813 was used to prepare red bean sourdough,after the analysis of the effects of the red bean sourdough on the freeze-thaw stability of frozen gluten dough,gluten starch dough and wheat starch red bean gel were conducted,its effects on rheo-fermentation characteristics of frozen dough,baking characteristics and flavor characteristics of frozen dough bread during the freezing storage were explored.Furthermore,the targeted use of Kluyveromyces marxianus combined with W.confusa QS813 to ferment red bean sourdough to improve the quality of frozen dough bread were also studied.Main research contents and conclusions were listed as follows:1.Preparation of red bean sourdough and study of the fermentation.After fermentation by W.confusa QS813 for 24h,the p H of red bean sourdough decreased from 6.32 to 4.34,and the corresponding TTA increased from 3.68 to 11.07,and the lactic acid and acetic acid content reached 106.97mmol/100g and 62.66mmol/100g,respectively.The fermentation quotient was1.71,and LAB(Lactic acid bacteria)cell count in sourdough was 1.51×10~8 CFU/g.The EPS content of red bean sourdough supplemented with 10%sucrose at 30?reached 18.68g/kg after24h fermentation.The fermentation of red bean sourdough degraded red bean protein into macromolecular peptides(MW above 10000 Da),small molecule peptides(MW below 500 Da)and free amino acids.As a result,the arginine(bitter amino acid)content in red bean sourdough decreased significantly,while the content of lysine increased.2.The effect of red bean sourdough fermented by W.confusa QS813 on the freeze-thaw stability of gluten and red bean dough were investigated.The results showed that EPS in gluten red bean dough prepared with W.confusa QS813 fermented red bean sourdough enhanced GMP aggregation,reduced the moisture migration of frozen gluten red bean dough,decreased the degree of GMP depolymerization and delayed the deterioration of the gluten protein configuration during the freeze-thaw cycles.The improvement of rheological properties and microstructure integrity were mainly attributed to the synergistic effect of EPS and sourdough acidification in the frozen gluten red bean dough system.The acidification environment was favorable for EPS functionality to delay GMP depolymerization through formation of hydrogen bonds and other chains and structures.3.The effect of red bean sourdough fermented by W.confusa QS813 on the freeze-thaw stability of gluten starch dough were investigated.The results showed that the EPS in the red bean sourdough enhanced the water binding capacity of the gluten starch dough,delayed water migration and enhanced the gluten starch dough's resistance to deformation caused by recrystallization.The acidification caused by sourdough fermentation was conducive to the interaction between EPS and the ingredients in the gluten starch dough,reducing the degree of GMP depolymerization during the freeze-thaw cycles,delaying the deterioration of the secondary structure of gluten protein and maintaining the integrity of the protein conformation,improving rheological properties and microstructure integrity.At the same time,addition of gluten to the gluten starch dough system helped protect the freeze-thaw stability of the gluten starch dough.4.The effect of red bean sourdough fermented by W.confusa QS813 on the freeze-thaw stability of starch red bean gel were investigated.The results showed that addition of red bean sourdough and gluten protein reduced the increase rate of water separation rate and freezable water content of starch red bean gel,and delayed the dehydration and shrinkage of starch red bean gel during freeze-thaw cycle treatment.The synergistic effect of the acidification of EPS and sourdough effectively reduced formation and recrystallization of ice crystals and aggregation and depolymerization of starch molecules in the system,effectively delaying the migration and redistribution of water in the system.This inhibited the long-term retrogradation of amylopectin and reducing the staling rate during long-term storage.The diluting effect of gluten on starch and its high-water holding capacity decreased the retrogradation rate of starch which resulted in reduction of the hardening rate of starch gel.In terms of microstructure,the starch gel containing red bean sourdough was denser and more uniform than CR after 5 freeze-thaw cycles and the network structure integrity was higher.5.The effect of red bean sourdough on rheo-fermentation and baking characteristics of frozen bread dough during freezing storage were investigated.The results showed that the high water holding capacity of EPS in red bean sourdough reduced the water migration of frozen dough,inhibited formation and recrystallization of ice crystals.This effectively alleviated the depolymerization of GMP,weakened the destruction of gluten protein network structure,and hindered the decrease of the survival rate of yeast,improved rheo-fermentation performance of the frozen dough,and improved the quality(specific volume,hardness,staling rate)of the frozen dough bread.In addition,red bean sourdough fermented by K.marxianus and W.confusa QS813 could promote the baking quality of frozen dough and its bread.6.The effect of red bean sourdough on the aroma characteristics of frozen dough bread were investigated.The results showed that the fermentation by W.confusa QS813 contributed to the metabolic decomposition of arginine in sourdough,while the symbiotic fermentation with K.marxianus contributed to the metabolic decomposition of cysteine in sourdough.The fermentation of mixed-bacteria was beneficial to the accumulation of aroma compounds in frozen dough bread such as free amino acids.Comparing the types of volatile aroma compounds of bread before and after 8 weeks of frozen dough storage,red bean sourdough fermentation increased the types of heterocyclic compounds,esters and acids.Consistent with the principal component analysis chart,heatmap analysis showed that bread flavor compounds from 8-week frozen stored dough were mostly lost and the peak areas of the major component flavor compounds was relatively small.This was attributed to the deterioration of gluten protein and accelerated decrease of yeast survival rate after frozen storage of dough.The red bean sourdough fermented by mixed-bacteria could protect the protein spatial configuration of the frozen dough better due to the stronger water holding capacity of EPS and WEAX,and delay the decrease of the aroma compounds content of the frozen dough more effectively.