Feasibility study on direct fermentation of soybean meal by Bacillus stearothermophilus under non-sterile conditions

Nutritional attributes and microbial metagenomic profile during solid-state fermentation of soybean meal inoculated with Lactobacillus acidophilus under non-sterile conditions

BACKGROUND

Soybean meal (SBM) is used widely in animal feed but it contains anti-nutritional factors (ANFs) such as protease inhibitors - immunogenic proteins that limit its utilization. Fermentative processes could help to reduce these ANFs. The aim of this study was to evaluate the nutritional attributes, bacterial community dynamics, and microbial metagenomic profile during the solid-state fermentation of SBM using a strain of the bacterium Lactobacillus acidophilus with or without pre-autoclaving treatment.

RESULTS

Following fermentation, there was a reduction in the pH and a concurrent increase in the population of lactic acid bacteria. Fermentation also resulted in an increase in both crude and soluble protein levels. Trypsin inhibitor levels decreased after fermentation, particularly in fermented SBM that had not been pre-autoclaved, with an inactivation rate higher than 90%. Moreover, high-molecular-weight peptides (44-158 kDa), specifically some polypeptides from the soybean immunogen glycinin and β-conglycinin, underwent degradation during the fermentation process. Bacterial community analysis revealed the dominance of the Lactobacillus genus in all samples, regardless of the treatments applied. Metagenomic profiling identified L. acidophilus as the dominant species in inoculated SBM, irrespective of whether pre-autoclaving was conducted or not.

CONCLUSION

This study demonstrates the feasibility of solid-state fermentation with L. acidophilus under non-sterile conditions to inactivate trypsin inhibitor and increase protein concentration and hydrolysate immunogen proteins into low-molecular-weight peptides in SBM. Lactobacillus acidophilus inoculum also inhibited the growth of undesirable bacteria. This knowledge contributes to our understanding of the potential applications of solid-state fermentation with L. acidophilus in improving the nutritional quality of SBM. © 2024 Society of Chemical Industry.

The process of solid-state fermentation of soybean meal: antimicrobial activity, fermentation heat generation and nitrogen solubility index

BACKGROUND

Bacillus amyloliquefaciens has excellent protease production ability and holds great prospects for application in the solid-state fermentation of soybean meal (SBM).

RESULTS

Among eight strains of bacteria, Bacillus amyloliquefaciens subsp. plantarum CICC 10265, which exhibited higher protease production, was selected as the fermentation strain. The protease activity secreted by this strain reached 106.41 U mL-1 . The microbial community structure differed significantly between natural fermentation and inoculation-enhanced fermented soybean meal (FSBM), with the latter showing greater stability and inhibition of miscellaneous bacterial growth. During fermentation, the temperature inside the soybean meal increased, and the optimal environmental temperature for FSBM was found to be between 35 and 40 °C. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and nitrogen solubility index (NSI) results demonstrated that solid-state fermentation had a degrading effect on highly denatured proteins in SBM, resulting in an NSI of 67.1%.

CONCLUSION

Bacillus amyloliquefaciens subsp. plantarum CICC 10265 can enhance the NSI of SBM in solid-state fermentation and inhibit the growth of miscellaneous bacteria. © 2023 Society of Chemical Industry.

Structural Characterization and Properties of Modified Soybean Meal Protein via Solid-State Fermentation by Bacillus subtilis

Soybean meal (SBM) is a high-quality vegetable protein, whose application is greatly limited due to its high molecular weight and anti-nutritional properties. The aim of this study was to modify the protein of soybean meal via solid-state fermentation of Bacillus subtilis. The fermentation conditions were optimized as, finally, the best process parameters were obtained, namely fermentation temperature of 37 °C, inoculum amount of 12%, time of 47 h, and material-liquid ratio of 1:0.58, which improved the content of acid-soluble protein. To explore the utilization of modified SBM as a food ingredient, the protein structure and properties were investigated. Compared to SBM, the protein secondary structure of fermented soybean meal (FSBM) from the optimal process decreased by 8.3% for α-helix content, increased by 3.08% for β-sheet, increased by 2.71% for β-turn, and increased by 2.51% for random coil. SDS-PAGE patterns showed that its 25-250 KDa bands appeared to be significantly attenuated, with multiple newborn peptide bands smaller than 25 KDa. The analysis of particle size and zeta potential showed that fermentation reduced the average particle size and increased the absolute value of zeta potential. It was visualized by SEM and CLSM maps that the macromolecular proteins in FSBM were broken down into fragmented pieces with a folded and porous surface structure. Fermentation increased the solubility, decreased the hydrophobicity, increased the free sulfhydryl content, decreased the antigenicity, improved the protein properties of SBM, and promoted further processing and production of FSBM as a food ingredient.

Effects of Fermentation on the Apparent Metabolizable Energy and Standardized Ileal Digestibility of Amino Acids in Soybean Meal Fed to Broiler Chickens

Two experiments were conducted to test the hypothesis that the apparent metabolizable energy (AME) and standardized ileal digestibility (SID) of amino acids (AA) in fermented soybean meal (FSBM) are greater than those in soybean meal (SBM). FSBM was produced by fermenting SBM with a mixture of Bacillus amyloliquefaciens, Lactobacillus acidophilus, and Saccharomyces cerevisiae. The fermentation process decreased trypsin inhibitor and crude fiber levels by 67.80% and 7.56%, while it increased the total amino acid content by 2.56%. In the first experiment, a substitution method was used to determine the AME and nitrogen-corrected AME (AMEn) of SBM and FSBM. A corn-SBM basal diet and two test diets consisting of 70% of the basal diet plus 30% SBM or FSBM were formulated. The results show that fermentation did not have an effect on the AME and AMEn concentrations of SBM (p > 0.05); the respective AME and AMEn values were 10.29 and 10.62 MJ/kg (DM basis) and 9.09 and 9.23 MJ/kg for SBM and FSBM. In the second experiment, a nitrogen-free diet was formulated to measure the endogenous AA flow, and the other two semi-purified diets containing SBM or FSBM as the sole source of AA were formulated. The results show that the AID and SID of isoleucine, leucine, phenylalanine, valine, cysteine, tyrosine, and aspartic acid were greater in FSBM than in SBM (p < 0.05). In conclusion, the fermentation of SBM by a mixture of B. amyloliquefaciens, L. acidophilus, and S. cerevisiae can improve its nutritional values and is a promising protein resource for broiler production.

Bioconversion of agro-food industrial wastes into value-added peptides by a Bacillus sp. Mutant through solid-state fermentation

Advances in microbial enzyme technology offer a significant opportunity for developing low-energy bioconversion solutions for industrial wastes as inexpensive feedstocks for useful products. In this short communication, two agro-food industrial wastes, chicken feather powder (CFP) and okara, were converted into peptides by a Bacillus licheniformis mutant using solid-state fermentation (SSF). The optimum SSF conditions for okara to CFP ratio, inoculum size, and time were 0.7 (7:10), 15%, and 90 h, respectively, which produced 185.99 mg/g peptides, with 910.12 U/g keratinase activity and 85.03% antioxidant scavenging activity. Compared to okara, CFP with mutant strain showed 11.28% higher keratinase activity and produced higher amounts of peptides (5.51%).

Application of ultrasound technology in the field of solid-state fermentation: increasing peptide yield through ultrasound-treated bacterial strain

BACKGROUND

The increase of peptide yield contributed to reducing the usage of antibiotics in solid-state fermented feed. Ultrasound technology is used in the field of liquid-state fermentation to improve yield of fermented products but has not been utilized in the field of solid-state fermentation (SSF). The main objective of this study was to investigate the feasibility of improving peptide yield in SSF products through ultrasound-treated bacterial strain.

RESULTS

The highest peptides content in soybean meal SSF products reached 153.28 mg g-1 , which increased by 15.05% compared with the control. This content value was acquired through treating the bacteria of Bacillus amyloliquefaciens by ultrasound before inoculating into soybean meal under the optimized mode and parameters (simultaneous dual-frequency ultrasound mode, frequency combination of 40/60 kHz, total power density of 40 W L-1 , time of 20 min, pulse-on and pulse-off times of 40 and 60 s, delayed inoculation time of 0 h). Fermenting with ultrasound-treated bacterial strain can effectively increase peptide yield, biomass and protease activity of soybean meal fermented products during the SSF prophase. After treating by ultrasound, the latent phase and logarithmic phase of the bacterial strain shortened by 1 and 3 h while the generation time reduced by 23.64%. In qualitative test of protease activity, diameter ratio (DR) value of ultrasound-treated bacterial cells enlarged by 12.0% compared with the control.

CONCLUSION

Peptide yield of soybean meal SSF products can be improved through ultrasound-treated bacterial inoculum, which attributed to the promoting effect of ultrasound treatment on growth activity and protease production capability of bacterial cells. © 2021 Society of Chemical Industry.

Study on the comprehensive utilization of solid residues of Flammulina velutipes and vinegar and their application as feed in Eisenia fetida earthworm culture

To explore the comprehensive utilization of agricultural wastes, solid-state fermentation was applied to residues of Flammulina velutipes (F. velutipes) and vinegar for use in culturing earthworms. Fermentation technology and earthworm culture technology were optimized by response surface methodology in this study. The optimal fermentation product for earthworm culture was obtained under an inoculum amount of 7.5%, fermentation temperature of 25.6 °C, pH 7.7 and protein content of 18.23%. The optimum culture conditions were a culture density of 18.4 individuals/dm³, an initial pH of 7.2 and a fermentation temperature of 26.8 °C. The daily weight gain multiplier of earthworms was 0.0387 units, and it increased significantly compared with that of the unfermented and cow dung groups. The fermented product of F. velutipes and vinegar residues could be used to culture earthworms and improve the metabolism and antioxidant capacities of earthworms. This provides a new way to comprehensively utilize agricultural waste resources.

Bacillus velezensis DP-2 isolated from Douchi and its application in soybean meal fermentation

BACKGROUND

Soybean meal (SBM) is the most common protein source used in the poultry and livestock industries. It has high-quality protein, an excellent amino acid (AA) profile, and positive isoflavone properties. However, the antigen proteins in SBM are unsuitable for young animals. The objective of this study was to identify a Bacillus strain that can degrade soybean antigen proteins, and to evaluate the feasibility of its application in SBM fermentation.

RESULTS

Bacillus velezensis DP-2 was isolated from Douchi, a fermented Chinese food. It degraded 96.14% and 66.51% of glycinin and β-conglycinin, and increased the trichloroacetic acid-soluble protein (TCAN) content by 5.46 times in the SBM medium. DP-2 could secrete alkaline protease and neutral protease, with productivities of 5.85 and 5.99 U mL-1 . It had broad-spectrum, antibacterial activities against Rhizopus nigricans HR, Fusarium oxysporum ACCC37404, Penicillium digitatum SQ2, Aspergillus flavus C1, Aspergillus niger ACCC30005, Trichoderma viride YZ1, Candida tropicalis CICC1630, and Salmonella sp. ZY. For SBM fermentation, the optimal inoculum rate, temperature, and fermentation time of DP-2 were 2.21 × 107 CFU g-1 , 37 °C, and 48 h, respectively. The fermented soybean meal (FSBM) was cream-colored and glutinous. Its crude protein (CP), soluble protein, and TCA-N content were improved by 13.45%, 12.53%, and 6.37 times, respectively. The glycinin and β-conglycinin content were reduced by 78.00% and 43.07%, respectively, compared with raw SBM.

CONCLUSIONS

Bacillus velezensis DP-2 has potential as a starter culture for SBM fermentation. © 2020 Society of Chemical Industry.

Microbial Biofilms in the Food Industry-A Comprehensive Review

Biofilms, present as microorganisms and surviving on surfaces, can increase food cross-contamination, leading to changes in the food industry’s cleaning and disinfection dynamics. Biofilm is an association of microorganisms that is irreversibly linked with a surface, contained in an extracellular polymeric substance matrix, which poses a formidable challenge for food industries. To avoid biofilms from forming, and to eliminate them from reversible attachment and irreversible stages, where attached microorganisms improve surface adhesion, a strong disinfectant is required to eliminate bacterial attachments. This review paper tackles biofilm problems from all perspectives, including biofilm-forming pathogens in the food industry, disinfectant resistance of biofilm, and identification methods. As biofilms are largely responsible for food spoilage and outbreaks, they are also considered responsible for damage to food processing equipment. Hence the need to gain good knowledge about all of the factors favouring their development or growth, such as the attachment surface, food matrix components, environmental conditions, the bacterial cells involved, and electrostatic charging of surfaces. Overall, this review study shows the real threat of biofilms in the food industry due to the resistance of disinfectants and the mechanisms developed for their survival, including the intercellular signalling system, the cyclic nucleotide second messenger, and biofilm-associated proteins.