| Lactic acid bacteria were important probiotics because they could inhibit the adhesion and growth of pathogenic bacteria in the gastrointestinal tract of animals and improved the immunity and growth performance of animals.In this study,the in vitro probiotic characteristics of Pediococcus pentosaceus NCU301,the process conditions for intensifying fermented soybean meal,and the parameters of microorganisms,organic acids,and carbohydrates during the fermentation process were studied.The main findings were as follows:(1)In vitro tolerance of NCU301.The survival rate of NCU301 in MRS liquid medium at pH 2.0 for 4 h was 84.19%;the survival rate was 84.97%after 24 h in MRS liquid medium containing 0.3%bile salt;the number of viable cells still reached more than 10~8 CFU/mL after 10 hours in artificial simulated gastrointestinal fluid.The results showed that NCU301 was well tolerated to the gastrointestinal tract.(2)Antibacterial properties of NCU301.Through the growth inhibition experiments of six common pathogenic bacteria,it was found that the fermentation broth and supernatant of NCU301 had better inhibitory effects on S.aureus of G~-bacteria and S.aureus of G~+bacteria than other pathogens,but the bacterial cell itself did not inhibit pathogens.The antibacterial substances secreted by NCU301 include lactic acid,protein,hydrogen peroxide,etc.The inhibition effects of these substances were not affected by temperature,but they were influenced by pH and had best inhibition effect in pH4 environment.(3)The process optimization of intensifying fermented soybean meal by NCU301.The number of viable cells of Lactobacillus was used as an indicator.The process conditions for the intensifying fermented soybean meal were optimized through single factor experiments and BOX-Behnken response surface analysis.Combined with the subsequent drying process,the optimum conditions were:fermentation time 50.0 h,fermentation temperature 30.0°C,substrate to water ratio 1:82,inoculum volume 8%,drying temperature 35°C,drying time 6 h.The amount of viable lactic acid bacteria reached 9.97×10~9 CFU/g after the final optimization.(4)Changes of microorganisms,organic acids,and carbohydrates during the fermentation of soybean meal.The study found that the content of lactic acid increased by 18.03 mg/g,the content of acetic acid decreased by 19.33 mg/g,the pH decreased from 6.23 to 4.70 in soybean meal,and the sucrose and glucose content decreased by26.4 mg/g and 1.41 mg/g,respectively.The fructose content increased by 1.66 mg/g.The content of,Lactobacillus,Bacillus,Escherichia coli and yeast in soybean meal was8.91 log(CFU/g),8.87 log(CFU/g),8.84 log(CFU/g),and 7.85 log(CFU/g),respectively;when soybean meal fermentation was fortified with NCU301,the p H decreased from the initial 6.07 to 4.36,the lactic acid content increased by 30.19 mg/g,the acetic acid content decreased by 9.99 mg/g,and the sucrose and glucose and fructose content decreased by 18.59 mg/g,3.12 mg/g and 0.18 mg/g.The live Lactobacillus counts increased from 7.15 log(CFU/g)to 10.06 log(CFU/g),the Bacillus counts decreased to 3.68 log(CFU/g),and the number of Escherichia coli and yeast were all lower than 10~2 CFU/g.No mold was detected during the two fermentation methods.Using the principal component analysis method to analyze the obtained data,the cumulative contribution rate of the two components with feature values greater than1 was 87.731%.The score diagram reflects that the components of soybean meal have been significantly changed at different fermentation time periods.Through high-throughput sequencing of microorganisms in fermented soybean meal in two ways,the results showed that the lactic acid bacteria in the fermented soybean meal promoted growth and reproduction,while other bacteria were significantly inhibited.(5)Changes in nutrient composition before and after soybean meal fermentation.The nutrient contents of soybean meal changed after natural fermentation and enhanced fermentation.After natural fermentation,crude protein,acid-soluble protein,and small peptides in soybean meal increased by 4.13%,42.67%,and 57.49%,and total free amino acids,phytic acid,trypsin inhibitor,and urease decreased by 12.36%and 17.88%,respectively.61.62%,79.31%;The total amount of crude protein,acid-soluble protein,small peptides,and free amino acids in soybean meal increased by 4.78%,36.04%,52.21%,and 19.10%,respectively,after intensive fermentation.Phytic acid,trypsin inhibitor,Urease decreased by 28.32%,89.56%,and 91.72%,respectively. |
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