Study On Isoflavone Transformation By Sourdough Fermentation And Its Baking Properties In Bread

Bread is the mainstream food in the world,and is one of the most nutritious and high quality food.Soybean isoflavone,an active ingredient enriched in bread,has the effects of anti-tumor,prevention of cardiovascular disease,osteoporosis,menopausal syndrome.A lactobacillus plantarum(Lactobacillus plantarum,strain CAU: 228)with high soybean isoflavone aglycone was screened through the 96 orifice method and high performance liquid chromatography.A functional and high yield of isoflavone aglycone sourdough bread was made.165 strains of lactic acid bacteria are isolated and purified from the 3 Moutai Qu starter(new Qu,old Qu,bean Qu),24 strains of lactic acid bacteria were screened using 96 orifice method with seven leaf color reaction which producing ?-glucosidase.HPLC method was used for quantitative analysis of isoflavone aglycone.3 strains with the highest isoflavone aglycone content were chosen: L1,D14 and X11.The yield of total isoflavone aglycone in L1 fermentation liquid was the highest,which was 0.61 mg/g soybean powder.D14 and X11 reached 0.52 and 0.49 mg/g respectively.After the 16 S rDNA sequencing,the homology between D14,X11 and Pediococcus pentosaceus strain SRCM100194 reached 99%.The homology between L1 and Lactobacillus plantarum strain LPL-1 reached 100%.The L1 strain with the highest yield of soybean isoflavones aglycone was used as an experimental strain for subsequent application.L1 was used as the fermentation strain to enrich the soybean isoflavone aglycone,and the optimum carbon source of the strain was optimized,sucrose was the best carbon source for L1.The yield of soybean isoflavones aglycone(mg/g soybean flour)was used as response value to optimize the fermentation conditions of L1 in soybean matrix by single factor and response surface optimization experiments.In order to facilitate the experimental operation,the best fermentation condition for soybean sourdough was: DY value 500,fermentation temperature 37°C,fermentation time 36 h,sucrose addition 2 g.Under these conditions,fitting by response surface software,we got the predicted value of 0.73 mg/g soybean powder,and the real soybean isoflavone aglycone yield was 0.73 mg/g soybean powder after fermentation.This has a higher correlation with the results of the response surface software.The scavenging ability of DPPH radical-scavenging activity reached 58.28%.The scavenging ability of ·OH radical-scavenging activity reached 75.02%.These antioxidant indexes showed that the antioxidant capacity of soybean flour fermented by L1 increased significantly.The total soybean isoflavone aglycone content in soybean dough(SSD)increased significantly,which was 9.87 times of the initial fermentation,while the isoflavone glucoside decreased significantly from the original 0.89 mg/g soybean powder to 0.39 mg/g soybean powder.The content of total soybean isoflavones was slightly higher than the initial fermentation.It can be seen that the soybean isoflavones aglycone were enriched in the fermentation process of soybean sourdough(SSD),and the nutritional value of dough is enhanced.The total phenol content firstly decreased and then increased from 3.83 mg GAE/g to 5.29 mg GAE/g.At the same time,after fermentation,the content of low molecular weight soybean peptide increased significantly,and the hydrolysis of high molecular weight soybean peptide could release a lot of free amino acids.The total free amino acid content in soybean sourdough(SSD)produced by L1 fermentation is 692.00 mg/100 g,which is 2.39 times higher than that of soybean dough(289.63 mg/100g).The content of essential amino acids increased from 35.09% to 46.03%.The above results showed that the antioxidant capacity and nutrition of soybean sourdough(SSD)were improved.Sensory evaluation results showed that the fermentation of sourdough could effectively improve the specific volume,texture and flavor of soybean bread,and enhance sensory scores and overall acceptability of soybean bread.Finally,functional soybean sourdough bread with high acceptability and soybean isoflavones aglycone was obtained.The total soybean isoflavones aglycone contents in soybean sourdough bread(SSB)and soybean bread(SB)were 6.39 mg/100 g and 2.18 mg/100 g.The functional soybean sourdough bread(SSB)rich in soybean isoflavones aglycone was prepared.Compared with wheat bread(WB),the volume and texture quality of soybean bread(SB)decreased,but the quality of soybean sourdough bread could be effectively improved after fermentation.After L1 fermentation,the specific volume of the sourdough bread(SSB)was significantly higher than that of the soybean bread(SB),and the hardness,adhesiveness and chewiness decreased significantly,the elasticity increased.The overall quality of the soybean sourdough bread(SSB)was improved.The total free amino acid content in soybean sourdough bread(SSB)is 128.06 mg/100 g,which is 2.02 times the total free amino acid of soybean bread(SB).The in vitro gastrointestinal digestion showed that the bioavailability(42.54% and 52.00%)of daidzein and genistein in soybean bread(SB)was significantly lower than that(65.11% and 63.57%)in soybean sourdough bread(SSB).The sourdough fermentation technology can greatly improve the bioavailability of bread.