| Bacillus spp.can remain in food easily due to form heat resistant spores.Surimi products spoilage is usually caused by Bacillus licheniformis.B.cereus has also been associated with food poisoning.Lactic acid bacteria(LAB),as a biopreservative agent,can inhibit pathogenic bacteria and spoilage microorganism.LAB strains with strong antagonistic activity to Bacillus spp.were isolated from fish intestine in the paper.The antimicrobial components and inhibition mechanisms of LAB were preliminary studied.It was applied to control B.licheniformis and B.cereus of silver carp fish ball using LAB crude extract.The aim was to develop a kind of lactic acid bacteria preservation agent for Bacillus spp..The main results were as follows:1.A total of 137 strains were derived from intestine of crucian carp,carp,silver carp,grass carp,bighead carp and mirror carp.44 strains of LAB were preliminary identified according to Gram stain method and catalase test.21 strains of LAB with inhibitory activity to B.licheniformis and B.cereus were screened from 44 strains of LAB.It showed that strains LY-19,LY-21,JY-22 and JL-18 have strong antagonistic effects to B.licheniformis and B.cereus.Strain LY-19 was identified as Lactobacillus sakei,strains LY-21,JY-22 and JL-18 were identified as Lb.plantarum by physiological and biochemical characteristics and 16S rRNA sequence.2.The antagonism of strains LY-19,LY-21,JY-22 and JL-18 were analyzed,the antagonistic activity was mainly from cell-free supernatants(CFS).It was the highest antagonistic activity from 20 h to 24 h under LAB strains growth.The inhibitory effects of acidic substances in CFS were eliminated.The inhibitory substances of LAB produced were preliminarily detennined as non-glycosylation bacteriocin determined by thermal treatment,enzyme sensitivity and pH.3.The inhitibory substances were obtained from strain JY-22 CFS by ethyl acetate extraction method,collecting solution by Sephadex G-50 chromatography.The results indicated that the eluent of 96 min,104 min and 112 min had inhibitory activity to B.licheniformis and B.cereus,The final product was detected to be one main peak with high performance liquid chromatography(HPLC).SDS-PAGE showed that its molecular weight was between 4.1-6.6 ku.4.The antagonism mechanisms of bacteriocin crude extract from strain JY-22 to Bacillus spp.were preliminarily studied.The MIC of bacteriocin crude extract was 6.0 mg/mL after extracted with ethyl acetate.The bacteriocin crude extract forced the growth curve of Bacillus spp.to drift,which indicated that the growth was completely inhibited.The conductivity,nucleic acid,protein,alkaline phosphatase(AKP)activity,Na+/K+-ATPase activity were analyzed,it was indicated that large amounts of macromolecules have been leaked because of the change of cell membrane permeability and the damage of integrity of the cell wall.The SEM results showed that the bacteriocin crude extract led to cells collapse and deformation,and some cells were completely broken.5.The effects of bacteriocin crude extract from strain JY-22 on preservation of silver carp fish ball under 4℃ were investigated.Results indicated that the sensory quality of the fish ball was improved by adding bacteriocin crude extract.The microorganism growth of silver carp fish ball was inhibited.It can make the counts of B.licheniformis and B.cereus be decreased by 2 and 1 orders of magnitude,respectively.And pH value and whitness of silver carp fish ball was decreased slowly and slightly.The addition of bacteriocin crude extract could extend shelf life 3 days at least. |
PDF Full Text Request