Studies On Fermented Wheat Flour By Exopolysaccharide-Producing Lactic Acid Bacteria And Its Effect On Baking Quality Of Eggless Cake

Cake attributes such as softness and sweet flavor is highly appreciated by consumers.Development of eggless cake caters to market demands for new products and reflects the diversity of baked products.In this study,the use of wheat flour fermented by exopolysaccharide(EPS)producing lactic acid bacteria(LAB)strain of Weissella confusa J28 in the production of eggless cake was investigated.Two LAB fermented wheat flour groups: sucrose supplemented to produce EPS(EPS+)and no supplementation(EPS-)were used for comparisons.Biochemical properties of fermented wheat flour were analyzed and effect of addition of the LAB fermented wheat flour on batter rheological properties,micro-bubble structure,baking characteristics,micro-network structure and storage characteristics of eggless cakes were explored.At the same time,the batter foam model and the protein model were established respectively to explore the mechanism of EPS affecting batter inflation and gas holding capacity and cross-linking of cake crumb protein network.In wheat flour,Weissella confusa J28 grew and adapted well;after 24 h of LAB fermentation,pH decreased to 3.79 and 3.56,and TTA increased to 5.75 and 6.08 mL in EPS+ and EPS-group,respectively.The yield of EPS reached 11.46g/kg in EPS+ group.Compared with EPS-group,the organic acid and reducing sugar content were lower and higher,in EPS+ group,respectively.The protease activity in the fermented flour increased(p<0.05)after 12 h of fermentation,and leveled off after 24 h of fermentation.Compared with unfermented wheat flour,the total free amino acid content increased by 2.19 and 2.09 in EPS-and EPS+ group,respectively;with all amino acids increasing(p<0.05)in content,except cysteine.Compared with control,rheological properties and micro-bubble structure of eggless cake batters showed that batter density decreased and viscosity increased in fermented flour cake group,while addition of EPS made batter bubbles more evenly distributed and with fewer abnormal bubbles.The batter foam model showed that the foaming ability of protein solutions could be improved and the stability of protein foam could be maintained by incorporating EPS during the whipping process.The mechanism was that the foaming ability of protein solution could be enhanced by EPS through changing molecular structure and exposing hydrophobic region of protein.At the same time,proteins could be cross-linked by EPS,reducing competitive adsorption of interfacial membrane proteins by emulsifiers,increasing thickness and viscoelasticity of interface membranes,and making protein foams more stable.Compared with control,baking properties such as specific volume increased,hardness decreased and color deepened in fermented flour cake group.The microstructure of cake crumb showed that the formation of protein networks was enhanced by addition of fermented wheat flour,as the protein networks were more continuous and uniform due to the cross-linking effect of EPS.Analysis of protein model mechanism showed that accessible thiol level of protein was raised by EPS without heat treatment.The reson was that α-helix and β-turn content of protein were reduced,random coil was increased by EPS through hydrogen bond induction and steric hindrance.This implied that spatial structure of protein was expanded and internal thiol was exposured.After heat treatment,a covalent cross-linked network of protein with β-sheet as the main conformation was formed.More covalent disulfide bonds of denatured protein were generated by EPS addition,so that the degree of protein network cross-linking was enhanced.The stability of protein network structures could also be enhanced by EPS through hydrogen bonding.The protein nutrition index showed that compared with control,in vitro protein digestibility and percentage of essential amino acids in fermented flour cake group increased,and nutritional characteristics of protein was better.The flavor characteristics showed that both the type and concentration of volatile flavor compounds increased in fermented flour cake group;thus,the flavor quality was improved.Principal component analysis showed that the flavor characteristics of unfermented and fermented flour cake groups were highly differentiated.Aldehydes and esters were the characteristic flavor compounds of EPS+ group,and the aroma was more intense.Sensory evaluation results showed that fermented flour cake groups scored more highly in terms of flavor,appearance,color and overall acceptability;with more significant results observed in eggless cakes prepared with fermented wheat flour with EPS(EPS+).Finally,the storage characteristics showed that the aging of eggless cakes was delayed and the hardening rate effectively reduced by addition of fermented wheat flour;but the degree of delay was limited by the level of acidification.Interestingly,the adverse effects of acidification were less pronounced in EPS+ group with more significant effect of inhibiting aging.This could be attributed to the water binding ability of EPS which reduced water migration and starch recrystallisation of the samples.