The Nutritional And Baking Characteristics Of Wheat Bran Containing Black Bean Sourdough Bread

Black beans and wheat bran ingredients are rich in protein and fiber,respectively.However,addition of black beans and wheat bran may be detrimental to wheat bread quality.Also,these ingredients may contain anti-nutritional factors such as phytic acid,among others.On the other hand,there are some off-flavor compounds present in black beans.Sourdough fermentation technology has effectively been used to improve the nutritional and baking quality of bread in modern baking scientific research.Therefore,this study aimed to combine the protein and fiber ingredients of black beans and wheat bran,respectively,with sourdough fermentation technology to improve bread quality.The phytase-producing Pediococcus pentosaceus L19 and the β-glucosidase-producing Lactobacillus fermentium J28 were used as sourdough starter for the sourdough bread.The main findings were as follows:Firsit,the influence of LAB fermentation on the biochemical characteristics of sourdough were investigated.In black bean and black bean-wheat bran substrates,the two LAB strains grew well and had a moderate acidification ability.Total number of colonies were in the range 9.5～10 log CFU/g in the stable phase,and the p H of the substrates decreased in the range 4.3 to 4.6.During the fermentation,lactic acid was mainly produced by L19,while,J28 produced both lactic acid and acetic acid.The two LAB strains showed different enzyme production characteristics.For instance,high phytase activity was detected in the two kinds of fermentation systems,and the phytase activity in L19 fermentation system was higher than that in the J28 fermentation system.β-glucosidase activity in J28 fermentation system increased then decreased,at the beginning and end of fermentation,respectively.But the β-glucosidase activity in the L19 fermentation system is extremely low.After 24 h of fermentation,the content of phytic acid in sourdough decreased by 59.79% to81.08%,while the proportion of soluble dietary fiber increased 31.39% to 44.15%.At the same time,the large proteins were gradually hydrolyzed into smaller peptides,while,the oligopeptides with molecular weight less than 1000 Da increased in the range 4.43% to16.08%.Second,the changes in physicochemical and microstructural properties of dough were investigated.Sourdough fermentation can improve the elasticity,extensibility and stability of dough.Dynamic rheological tests show that the dough’s viscoelastic properties tend to be balanced.Particularly,the physical properties of J28 sourdough dough are most similar to wheat dough.In addition,LAB sourdough fermentation can promote gas production of yeast,the final dough heights were in the range 69.4 mm to 77.6 mm.LAB fermentation can promote the hydration of gluten protein.Correspondingly,the disulfide bond content in the dough were significantly increased,while the free sulfhydryl group content decreased.Microstructural observations revealed that small gaps in the formed gluten network with close and regular distribution.At the same time,the secondary structure of the protein was changed from β-sheet,random curling to α-helix and β-turn.Correlation analysis showed that strong and negative correlations were observed between β-sheet and random curling content with p H.And the soluble dietary fiber also showed an inversely proportional relationship with β-sheet content(-8.01).There were no correlation between organic acid,α-amino nitrogen content and protein secondary structure.Also,the nutritional and beaking quality of bread were elaborated.Compared with the unfermented group,the total free amino acid content in sourdough bread increased by 29.46%to 57.35% respectively.In particular,the essential amino acid contents significant increased by 1.74 to 2.84 times relative to that of the unfermented breads.In addition,the dietary fiber content of sourdough bread with wheat bran was higher than 6%,while the protein content of four kinds of sourdough bread was as high as 13.82%～14.04%.After LAB fermentation,the in vitro protein digestibility of the four kinds of sourdough bread significantly improved.Among them,the in vitro protein digestibility was better in L19 than J28 fermented group,with values of L19 black bean sourdough bread and L19 black bean-wheat bran sourdough bread observed at 73.19% and 68.92%,respectively.The protein nutritional evaluation also indicated that the essential amino acid index(EAAI),biological value(BV)and nutritional index(NI)of sourdough bread were significantly improved.Finally,the flavor and storage characteristics of bread were investigated.A total of 76 volatile compounds were identified in seven kinds of bread.Alcohols are the major volatile compounds in bread,which was in the range of 47.82% to 67.48%.LAB fermentation can reduce the volatile components of aldehydes introduced by black beans and wheat bran,while the content of volatile acids in sourdough bread was 4.12 to 15.25 times relative to that of unfermented group.In addition,kinds of esters in the four types of sourdough breads were also significantly increased.Heatmap analysis showed that the two LAB strains have different aromatic profiles,they could be clearly distinguished from the unfermented group.The flavor research based on the electronic nose further indicated that the characteristic compounds among different bread are acetic acid,ethyl acetate and ethyl nonanoate.During the storage period,sourdough can effectively reduce the water loss of bread and delay the recrystallization of starch,thus reduce the hardening rate of bread crumb.