جستجوی مقالات مرتبط با کلیدواژه « لاکتوکوکوس لاکتیس » در نشریات گروه « صنایع غذایی »

Nisin is a biological bacteriocin with many functions against food pathogenic bacteria. The disadvantages of chemical preservatives in foods have attracted attention to natural preservatives such as nisin. This study evaluated the antimicrobial properties of nisin extracted from Lactococcus lactis isolated from goat milk. Ten goat milk samples were collected from around Kerman city under sterile conditions, and Lactococcus lactis were isolated in the selected environment of Eliker-trimethoprim. Biochemical tests were used to Strain identification and nisin gene confirm by polymerase chain reaction with specific primers was used. HPLC method was used to confirm the presence of nisin using bacterially extracted proteins. The antibacterial properties of nisin were performed by disk diffusion agar method against Staphylococcus aureus, Bacillus cereus, Acinetobacter baumannii, and Pseudomonas aeruginosa. The minimum inhibitory concentration of bacteriocin was performed by Provide serial dilution in a microtiter plate. One of the four strains of Lactococcus lactis was identified and selected with the best growth conditions for further investigation. The presence of the nisin gene in Lactococcus lactis was confirmed by a specific primer and polymerase chain reaction method. The amount of nisin produced protein was 41.5 mg/kg. The diameter of inhibitory zone for Staphylococcus aureus, Bacillus cereus, Acinetobacter baumannii, and Pseudomonas aeruginosa were 13, 17, 14, and 0, respectively, and minimum inhibitory concentrations for extracted nisin were in dilutions of 10-5, 10-6, 10-5 and 10-1, respectively. Therefore, nisin extracted from Lactococcus lactis in goat milk can be a suitable substitute for chemical preservatives.

As the technological point of view, cheese is a nutritious environment for growth of several of foodborne pathogens such as Staphylococcus aureus. Although, application of chemical and natural preservatives is common in prolongation of shelf-life of dairy products, so many researches are still running to find alternatives solutions. In this study, the effect of three strains of lactococcus lactis named as JP51, FK23 and DC103 was evaluated on viability of S. aureus in cheese. The produced cheese samples were analyzed for chemical composition and viability of S. aureus during period of 20 days of storage. The results showed that all three strains were able to significantly reduce the number of viable S. aureus in comparison to control. According to our results, the cheese manufactured by strain JP51 had the lowest number of S. aureus (2.00 log cfu/g) after 20 days of storage. Subsequently, current study showed that L. lactis isolate JP51 can be considered as potent natural antibacterial starters for cheese production. However, it would be necessary to evaluate its effect on physical and sensorial properties of cheese.

Probiotics have several advantages for human health. Since most of the probiotic foods are dairy products, they cannot be consumed by humans who are allergic to milk proteins or have severe lactose intolerance. While looking for alternative food matrices, the suitability of carrot juice as a raw material for the production of probiotic food with Lactococcus strain (L. lactis) isolated from local cheese was investigated. Pasteurization of freshly prepared carrot juice at 85°C for 5 min decreased the microbial population and enzymes are disabled (In particular peroxidase). The initial Lactococcus strain concentrations was 109 cfu/5ml of carrot juice, and were kept viable up to the end of fermentation (30 days).Tested Lactococcus lactis strain were capable of growing well on pure carrot juice without nutrient supplementation. Due to intense metabolism of the bacteria strain, carrot juice media were acidified to a pH level of less than 4.During fermentation, the amounts of sugars decreased significantly so that about 50% of which was taken after 24 hours. Degradation of carotenoids was less than 2%. In the case of phenolic compounds the reduction was minimal so that more than 80% of the total phenolic content of Carrot juices was retained in the final product.

Molds can be noted as one of the major factors in bread corruption that mainly caused by Aspergillus, Fusarium and Penicillium. In addition to the economic losses caused by mold, types of toxins produced by them can also cause health problems. Chemical preservative such as propionic and sorbic acids are mainly used for preventing mold growth that it is not receptive to consumers. In recent years due to increasing public awareness, Customers demand to reduce the use of chemicals and the use of natural preservatives. Lactic acid bacteria are one of the biological preservatives that because of the antimicrobial properties and in some cases due to the positive effects on organoleptic properties have received much attention. In this project, the effect of spraying the bacterium Lactococcus lactis PTCC 1336 at three concentrations (zero, 104 cfu /cm2 and 106 cfu /cm2) and also the combined use of calcium propionate in three levels , zero, 2 and 4 % (w/w) on improving the duration of preservation and its effect on organoleptic properties of bread and also its effect on reducing the amount of calcium propionate was investigated. In those bread, the quantity of pH, acidity, and the amount of mold formation (macroscopic and laboratory observations) were measured. The results showed Spraying bacterium Lactococcus lactis PTCC 1336 on bread Can be more powerful Compared with calcium propionate Compared with calcium propionate reduces the mold. So the least amount of mold at the sample M3P3 (Samples containing 106cfu/cm2, 0.4% PC) observed. as well The results showed concomitant use of Lactococcus lactis PTCC 1336 and calcium propionate Activity on mold synergistic effects are produced.

In recent years the increase in milk production worldwide on one hand and reduction in natural sources of "rennin" on the other, has resulted in significant decrease in rennin-produced cheese. In this research, it was attempted to clone the caprin prochymosin gene in the lactococcus lactis. If succeeded, the results of this work would allow production of cheese without the need for adding exogenous rennin or low quality fungal enzymes. The prochymosin gene which had been previously cloned in pET plasmid in E. coli BL21 was amplified by PCR and was then isolated from the agar gel, ligated to plasmid PTZ and cloned in E. coli GM. The prochymosin gene was cut by enzyme and ligated to L. lactis plasmid PNG and cloned in E. coli MC1061. The plasmid then isolated from E. coli MC1061 and transferred to L. lactis NZ9000 and recombinant cloned were sequenced.

In this research diacetyl production as a buttery flavor in food industries by Lactic Acid Bacteria (LAB)، Lactococcus and Leuconostoc genus was investigated. Batch fermentation process accomplished on MRS (De Man، Rogosa and Sharpe medium) broth medium، medium based on whey powder and based on skim milk powder at different conditions of temperature، agitation speed، glucose as carbon source، tri-sodium citrate as precursor of diacetyl production، inoculum، catalase enzyme، bovin blood as heme protein source and CuCl2. Optimum conditions were determined for achivement of highest production yield. This research indicated that the optimum fermentation conditions for diacetyl production by LAB were: 32º C، 180 rpm، glucose 6 g/l،tri-sodium citrate 5g/l، inoculun 5%، catalase enzyme 6 ml/l، bovin blood 4 g/l، CuCl2 15 mg/l. Finally، for production of diacetyl، a fermenter was used with 10 liter volume، inoculum size 5 % (v/v) with working volume of 6. 5 liters. Agitation and temprature were maintained at 180 rpm and 32ºC، respectively. Diacetyl concentration under optimized condition in fermenter was obtained as 945 mg/l.