Gamma-aminobutyric Acid Fermentation Technology Using Fish Peptone As Substrate And The Applications

y-Aminobutyric acid(GABA)is a natural non-protein amino acid,which can serve as a mammalian inhibitory neurotransmitter and has good physiological functions such as lowering blood pressure,promoting reproduction,calming the mind.In addition,GABA also plays many important roles in the process of plant growth and development,and has good effects in resisting non-Biotic stress such as drought and cold,saline alkali,high temperature and hypoxia,and preventing Biotic stress such as microbial pathogens and pests.This thesis studied the process and technology of GABA production by Lactobacillus brevis fermentation using fish peptone as the substrate.The strains for high GABA expression were selected through UV mutagenesis,and the conditions of shaking flask culture were optimized to increase GABA production.The batch fermentation was conducted in a bioreactor to verify the feasibility of large-scale production.Moreover,the relevant promoting effects of the fermentation broth containing GABA on the plant growth were explored and verified.Firstly,the initial GABA strain was isolated from yoghurt and identified as Lactobacillus brevis with certain GABA synthesis ability.After ultraviolet-LiCl mutation,a high-yield strain with stable genetic characteristics was obtained.The mutant strain reached a GABA expression of 16.5 g/L after 72 h fermentation,which was 51.3%higher than the original strain.Secondly,the shaking flask culture conditions of GABA were optimized using single factor experiments,Plackett-Burman design,steepest slope experiments,and response surface design.Th key factors such as glucose,sodium L-glutamate,and manganese sulfate with significant positive effects were selected.Corresponding models were established through steepest slope experiments and response surface design to obtain the optimal culture conditions.The GABA production reached 26.9 g/L,showing an increase of 63%compared to that before optimization.GABA batch fermentation was conducted in a bioreactor to verify the possibility of scale-up production,and the fermentation was optimized.The optimal dissolved oxygen conditions were aerobic fermentation for 24 hours and then transferred to anaerobic fermentation.The pH was maintained at 5.0,and the cumulative production of GABA reached 80.2 g/L after four rounds of fed-batch fermentation.Finally,the fermentation broth containing GABA was used as an additive to prepare fish peptide fertilizer.The abilities of watermelon plants to resist drought,freeze,and disease during growth and development were investigated.After one month of application,the yield of watermelon per unit of area reached 1425.4 kg,which was 279.3%,34.1%,and 64.9%higher than that of no fertilizer and the other two common fertilizers in the market,respectively.The results demonstrate the feasibility of using aquatic waste as substrate to ferment and produce GABA for use as a plant growth regulator.