Isolation Of Antifungal Lactic Acid Bacteria And Their Effect On The Quality Of Rye Bran Sourdough Bread

Rye bran is rich in dietary fiber,ferulic acid and other nutrients,which is nutritious,but the texture of bread will deteriorate with the addition of rye bran.In addition,bread is susceptible to fungal contamination,which leads to a shorter shelf life.Some lactic acid bacteria(LAB)strains have strong antifungal activity,and sourdough inoculated with LAB can extend the shelf life of bread and improve the quality of bread.In this study,LAB with strong antifungal activity were screened by double-layer plate method and microplate method,and their potential antifungal compounds were initially analyzed.Rye bran sourdough was prepared by inoculation with antifungal LAB,and their effects on the processing and nutritional properties of bread dough and bread were studied,and the main results were as follows:(1)Aspergillus fumigatus and Aspergillus flavus isolated from moldy rye bran bread and Aspergillus niger and Penicillium chrysogenum preserved in the laboratory were used as indicator bacteria,and Lactiplantibacillus plantarum G8 and Leuconostoc mesenteroides D3 with strong antifungal activity were isolated by double-layer plate method and microplate method,and their potential antifungal compounds were preliminarily identified as organic acids.(2)The results of antifungal capacity of Lactiplantibacillus plantarum G8 and Leuconostoc mesenteroides D3 fermentation supernatants treated with neutralized p H,heating,addition of catalase or different proteases showed that the potential antifungal compounds are organic acids.(3)Lactiplantibacillus plantarum G12 and Leuconostoc mesenteroides D9 with weak antifungal activity were selected as the control LAB for this study.Lactiplantibacillus plantarum G8,G12 and Leuconostoc mesenteroides D3,D9 were inoculated into rye bran to prepare sourdough,and RN(naturally fermented)rye bran sourdough was used as the control group to study the physicochemical properties of different rye bran sourdoughs.LAB maintained good growth capacity in rye bran,and the number of LAB in rye bran sourdoughs increased to 9.38 lg(CFU/g),9.67 lg(CFU/g),9.09 lg(CFU/g),and 9.09 lg(CFU/g)for D3(inoculated with Leuconostoc mesenteroides D3),G8(inoculated with Lactiplantibacillus plantarum G8),G12(inoculated with Lactiplantibacillus plantarum G12),and D9(inoculated with Leuconostoc mesenteroides D9),respectively.The p H of rye bran sourdough decreased continuously and the total titratable acidity(TTA)increased continuously during fermentation.Lactiplantibacillus plantarum G8 had the strongest acid production capacity,with a TTA of 32.73 m L after 24 h of fermentation,followed by Leuconostoc mesenteroides D3 with a TTA of 31.41 m L.The relative contents of organic acids and fatty acids with antifungal activity in D3 and G8 rye bran sourdoughs were overall higher compared to RN,D9 and G12 rye bran sourdoughs.The contents of lactic acid in G8 and D3 were 31.97 mg/g and 36.08 mg/g,which increased by 507.8% and585.9%,respectively,compared to RN.The contents of acetic acid in G8 and D3 were 4.24mg/g and 1.27 mg/g.The addition of antifungal LAB could improve the antioxidant activity of rye bran sourdough.G8 rye bran sourdough had the highest free total phenol content(228.83 mg/100g),followed by D3(207.06 mg/100g).G8 and D3 rye bran sourdoughs inoculated with antifungal LAB starters exhibited strong DPPH and ABTS radical scavenging activities.(4)The characteristics of rye bran bread dough were investigated using D9 and G12 bread doughs as negative controls and RN and RB(without sourdough)bread doughs as controls,and it was found that most of the starch granules in bread doughs with rye bran sourdough were distributed in the gluten protein network structure in an orderly manner.The percentage of β-sheet and α-helix secondary structures in the bread doughs inoculated with antifungal LAB starters increased and had a more orderly gluten network structure.The total percentage of β-sheet and α-helix secondary structure in G8 was the highest(53.00%),followed by D3(49.61%).(5)In addition,the addition of LAB could reduce the baking loss rate of bread,increase the type and content of volatile flavor substances and reduce the hardness,gumminess and chewiness of bread,especially Lactiplantibacillus plantarum G8 and Leuconostoc mesenteroides D3 with strong antifungal activity.The addition of antifungal LAB could prolong the antifungal effect period of bread,and the antifungal effect period of G8 and D3 was delayed by 8 and 9 days compared to RB,respectively.Moreover,the addition of antifungal LAB could increased the total free amino acid content,improve the in vitro protein digestibility of bread,and G8 bread had the highest in vitro protein digestibility(76.68%),followed by D3(76.32%).The sensory scores of bread inoculated with LAB increased in all aspects compared to RN,and G8 had the highest sensory scores in terms of odor.Compared to RB,the addition of rye bran sourdough could reduce the specific volume of bread.Overall,the addition of Lactiplantibacillus plantarum G8 and Leuconostoc mesenteroides D3 could improve the processing and nutritional properties of bread dough and bread.