Antibacterial Activity of Lactic Acid Bacteria and Extraction of Bacteriocin Protein

Biopreservation systems in foods are of increasing interest for industry and consumers. Bacteriocin producing Lactobacillus spp. is considered Generally Recognize as Safe (GRAS), useful to control the fast development of pathogens and spoiling microbes in food and feed. Lactobacillus spp. was isolated from traditional winter fermented vegetable cucumber & carrot by the use of selective media. Especially De Man, Rogosa and Sharpe (MRS) Agar media were used to isolate the Lactobacillus species. Morphologically identified by gram staining & colony morphology. Biochemically recognized by catalase, oxidase, MRVP & carbohydrate fermentation test. Antimicrobial activity of Lactobacillus spp. was confirmed by Well Diffusion Method. Molecular characterization of bacteriocin protein and molecular weight determined by SDS PAGE method. The isolate was found to be facultative anaerobic, Gram positive, and catalase negative. The result of antimicrobial activity measured by the Arbitrary Unit (AU/ml) of zone of the inhibition. Six isolates found from the sample but most activities exhibited isolate 4 against Bacillus megaterium (55 mm) zone of diameter. The molecular weight of the washed bacteriocin was calculated to be about 40 kDa (Isolate 1) and 15 kDa & 30 kDa (Isolate 5). Bacteriocin protein reduces chemical preservatives and uses in future as biopreservative in food industry.

The Use of Str Mutations for Enhancement of Hydrogen Peroxide Formation by Lactobacillus Delbrueckii MH-IO at Refrigeration

The strains ofLactobacillus delbrueckii subsp, lactis widely used in food preservation due to ability produce high amount of hydrogen peroxide at refrigerator temperatures to inhibit food-borne pathogens and psychrophilic spoilage microorganisms. In order to improve of bio-preservation efficacy ofL. delbrueckii MH 10 mutations causing resistance to streptomycin （str） were used. Among UV-mutagenized population of L. delbruecla＇i three str mutants producing high amounts of H2O2 were selected. Sir mutants produced significant amounts of hydrogen peroxide 50-60 μg/ml in sodium phosphate buffer （0.2 M, pH 6.5） and in beef broth （BB） at 5 ℃ for 5 days submerged cultivation without of growth. Evaluation mutants antibacterialactivity at refrigeration temperatures against food-borne pathogen Escherichia coli O157：H7 revealed elimination of pathogen total number up to practically undetectable amount for 3 days. In case of solid-state cultivation on agar-based medium, disks soaked by mutant cells suspensions formed larger inhibitory zones on E. coli O157：H7 lawn for one-day cold exposition. The size of inhibition zone depends on concentration of LAB cells. Str mutants L. delbrueckii reduced initial amount 2 - 105 of E. coil O 157：H7 in ground beef up to 3 log for 3 days of solid-state cocultivation when the wild strain reduced only 2 log. The application ofL. delbrueckii mutants did not cause any changes in sensory characteristics of ground beef, moreover promotes expanding of shelf-life due to inhibition of psychrophilic spoilage microorganisms.

Nano and microencapsulation of bacteriocins for food applications: A review

The increasing demand for prolonging food shelf life and inhibiting food spoilage and pathogenic microorganisms lead to development of novel biopreservatives and conservation methods. Antimicrobial peptides derived from microorganisms like bacteriocins are considered as a major alternative to the application of chemical preservatives in food products. Direct addition of purified antimicrobial peptides into food matrix results in reduced antibacterial activity due to the interaction of peptides with food components. Nano- or microencapsulation process can protect biopreservatives against many adverse conditions and controlled release of the agents efficiently prevent microbial contamination and food spoilage. This review focuses on the most frequently used chemical, physical and mechanical encapsulation methods for various antimicrobial bacteriocins including liposome entrapment, coacervation, emulsification, spray-drying, and vibrating technology. The most recent applications of nano- or microencapsulated antimicrobial bacteriocins with emphasis on nisin and pediocin in various food products like dairy, meat products and fruit juice have been discussed.

Effect of protective cultures on spoilage bacteria and the quality of vacuum-packaged lamb meat

Protective cultures,as natural antimicrobials,have the ability to suppress the growth of spoilage bacteria and can potentially be used to extend the shelf-life of fresh meat and help reduce food waste.As there have been limited reports on the application of this approach in fresh red meat,the aim of this study was to evaluate the potential and practicality of this approach for red meat shelf-life extension based on the antimicrobial efficacy and quality impact of selected protective cultures.Two protective cultures(one containing Lactobacillus sakei and the other containing Staphylococcus carnosus and L.sakei)were applied to chill-stored(4℃)vacuum-packaged lamb meat to determine their effects on spoilage bacteria as well as non-microbiological meat quality over a 20-day storage period.These protective cultures dominated the microbiota throughout storage and effectively suppressed the growth of common meat spoilage bacteria,Brochothrix thermosphacta,Pseudomonas spp.,and Enterobacteriaceae.Meat color(measured in CIE L*a*b*color space)changed slightly in culture-treated samples in the later stage of storage,but the changes were not unacceptable based on previously reported thresholds for consumer acceptability.The mixed culture containing additional S.carnosus exhibited a slightly stronger inhibitory effect against the spoilage bacteria but also caused more changes in meat color.Protective culture addition did not significantly affect meat pH,texture,or microstructure.Overall,these results demonstrated the potential of biopreservation using protective cultures for fresh red meat shelf-life extension.