| Peptides performed several benefits for the growing of livestock and poultry because of their multiple biological activities.Therefore,peptide is a kind of green,safe and highly effective alternative product to antibiotics.Presently,animal feeds are mainly prepared by solid-state fermentation.It is of great significance to improving quality of feeds and to antibiotics reduction by increasing the pepitdes content in fermentation products.However,many problems were still existed in the production process of fermented feed,such as insufficient mechanization,difficulties in realizing large-scale production,low yield rate of peptides,unstable quality and lack of relevant standards.It is necessary to introduce new technologies to promote industrial progress.Ultrasound technology already has a good research foundation in the field of assisting fermentation to improve product yield.Thus,this study tried to apply ultrasound technology into production process of fermented feeds.Effects of ultrasound-treated inoculated strain of Bacillus amyloliquefaciens(B.amyloliquefaciens)on peptides yield in soybean meal solid-state fermentation(SSF)products were studied.Additionally,the omics technologies were utilized to study molecular-level impacts of ultrasound treatment on the bacterial cells.According to the results of omics,the promotion effects of ultrasound treatment on endospores germination were detected.Then,mechanisms of improving peptides yield in SSF products by ultrasound-treated inoculated strain were preliminarily explored.Specific researches and major conclusions are as follows:(1)Inoculum prepareation of B.amyloliquefaciens and optimization of soybean meal SSF conditionsThe strain used in this study performed effective production ability of protease,amylase and cellulose.The optimal culture medium was nutrient broth(NB)culture medium.The optimal conditions of SSF were as follows: use unrushed soybean meal as fermentation substrate,fermentation temperature was 37?,inoculation rate was 10(v/m),solid-liquid ratio was 1:1(m/v)and fermentation time was 2.5 d.(2)Effects of ultrasound-treated inoculated strain on peptides yield in soybean meal SSF productsThe peptides content in SSF products was used as the evaluation indicator in the experiments.The optimal results were as follows: bacterial activation time of 10 h,simultaneous dual-frequency ultrasound mode,frequency combination of 40/60 k Hz,total power density of 40 W/L,time of 20 min,pulse-on and pulse-off time of 40 s and 60 s,ultrasound treatment performed once,inoculating the strain immediately after ultrasound treatment.Under these conditions,the peptides content in SSF products reached 153.68 mg/g,which increased by 15.57% compared to the control.(3)Effects of ultrasound-treated inoculated strain on process and products of SSFThe ultrasound-treated inoculated strain promoted the efficiency of soybeen meal SSF.This was because that ultrasound treatment accelerated the growth rate of the bacterial cells.Additionally,protease activity qualitative test manifested that protease and amylase activities in SSF products in ultrasonic treatment group were higher than those in control group.Additionally,ultrasound treatment performed no negative effect on the degradation of anti-nutritional factors during soybean meal fermentation.Similar results were acquired in the scaled fermentation test compared with the laboratory test,which testified the feasibility of improving peptides yield in soybean meal fermentation products through ultrasound-treated B.amyloliquefaciens.(4)Omics analysis of effects of ultrasound treatment on bacterial cells of B.amyloliquefaciensOmics researches revealed that effects of ultrasound treatment on B.amyloliquefaciens at molecular level mainly involved in the following aspects: 1)promote the formation of ribosomes and RNA polymerase,accelerate transcription and translation process;2)accelerate synthesis of essential substances related to basic life activities(lysine,asparagine,folic acid and cysteine);3)stimulate stress response of bacterial cells under adversities and improve p H maintenance ability;4)accelerate flagellin synthesis and improve cellular sports performance;5)reduce TCA cycle productivity speed and accelerate energy storage;6)accelerate biosynthesis of peptidoglycan and lipoteichoic acid,promote cell wall repair;7)accelerate DNA replication;8)accelerate synthesis of aminoly-t RNA and improve efficiency of protein synthesis.Further analyzation of omics data manifested ultrasound treatment performed no significant effect on enzyme production of single bacterial cell of B.amyloliquefaciens,but it improved resistance of cells and promoted germination of endospores.(5)Effects of ultrasound treatment on spore germinationUltrasound performed promotion effect on endospore germination.Pearson correlation analysis showed that the increase of peptides yield in soybean meal SSF products was related to the endospores germination promoted by ultrasound.Growth curve and protease activity determination demonstrated that ultrasound treatment can improve the growth and total enzyme production of germinated endospores and vegetative cells,which might be important reasons for the increase of soybean meal SSF efficiency.(6)Preliminary studies on the mechanisms of improvements of endospores germination rate and peptides yield in SSF products of ultrasound-treated inoculated strainUltrasound treatment performed effects of increasing dissolved oxygen,de-agglomeration and reducing viscosity of bacterial strain suspension.The increase of dissolved oxygen content in bacterial strain suspension benefited to promoting vegetative cells growth and endospores germination,which would accelerate the increase of biomass and total protease activity at early satge of soybean meal SSF.The cells dispersion and viscosity decrease of inoculum can improve the dispersion uniformity of bacterial cells after inoculating into soybean meal,which benefited the sufficient utilization of substrate.As a result,the strain growth and fermentation efficiency would improve. |
PDF Full Text Request