Synergistic antimicrobial effect of lactocin AL705 and nisin combined with organic acid salts against Listeria innocua 7 in broth and a hard cheese

The effectiveness of antimicrobial mixtures against Listeria innocua 7, used as a L. monocytogenes surrogate, was investigated in broth and a food system. Synergistic effects were found for nisin (Nis), potassium sorbate (PS), calcium propionate (CP) and sodium lactate (SL), Nis + PS being the most effective binary mixture that exhibited listericidal activity in broth. To assess the effect of adding lactocin AL705 (AL705) to Nis + organic acid salt combinations, tridimensional isobolograms were generated. Sub-MIC combinations of the antimicrobials exerted bactericidal activity against L. innocua 7 after AL705 addition to the binary mixtures. However, when applied on Sardo cheese contaminated with L. innocua 7 (initial inoculum 4.45 ± 0.06 CFU g⁻¹), only Nis + PS + AL705 produced count reductions respect to the control, reaching 3.04 ± 0.35 CFU g⁻¹ counts after 15 days at 15 °C. Ternary combinations containing AL705 showed potential to reduce antimicrobial usages for L. innocua 7 inhibition.     

The Use of Biopreservatives in the Control of Bacterial Contaminants of Sugarcane Alcohol Fermentation

ABSTRACT: Efficacy and safety of biopreservatives were studied for microbiological control of alcohol fermentation. Minimum inhibitory concentrations of nisin and lysozyme, and combinations with EDTA and Tween 20, were determined for Lactobacillus plantarum, L. fermentum , and L. confusus. The highest MIC value for nisin was 9.0 ppm for L. fermentum. Lysozyme was efficient against L. plantarum (700 ppm). A 2⁴ factorial design was used to study the effect of biopreservatives and potentiators on the growth kinetics of Lactobacillus fermentum. The combination of 8.6 ppm of nisin plus 0.1% of Tween 20 delayed the lag phase by 12 h. The biopreservatives did not affect the fermentation kinetics of Saccharomyces cerevisiae.     

Quantification of Factors Which Influence Nisin's Inhibition of CIostridium botulinum 56A in a Model Food System

We modeled nisin's anticlostridial activity and assessed the antagonistic or potentiating influences of food ingredients. The model systems contained yeast extract, proteose peptone, and glucose; were supplemented with protein (0.075, 0.75, 7.5% w/v), phospholipid (0.075, 0.75, 7.5% w/v), or soluble starch (5, 17.5, 30% w/v); and were adjusted to pH 5.5, 6.0, or 6.5. Samples inoculated with 10⁴/mL spores were incubated at 15, 25, or 35°C. Statistical analysis developed an equation (r²= 0.76) that modeled the response and identified temperature as the most significant (α 0.001) variable. Nisin lost effectiveness with increasing temperature. Nisin concentration had significant positive and phospholipid negative, linear effects. Many interactive effects were significant (α 0.20). Nisin inhibited C. botulinum until its residual level dropped below a threshold, which decreased from 154 IU/mL at 35°C to 12 IU/mL at 15°C.     

二剂量法测定乳链菌肽效价及其C++运算程序

准确测定乳链茵肽效价是发酵法工业化生产乳链茵肽很重要的环节．效价检测过程中影响因素很多，其中标准品和样品所产生差异的一些因素对测定有很大的影响．本文利用二剂量法检测乳链茵肽效价，检测过程中只需研究样品溶液和标准品溶液对检测造成的影响，排除了其它影响因素：确定了效价计算的C 运算程序，避免了通过标准曲线法计算效价产生的误差．大幅度提高了测定乳链茵肽效价的准确性。     

Evaluation of the effects of sodium chloride,potassium sorbate,nisin and lysozyme on the probability of growth of Clostridium sporogenes

The aim of this study was to evaluate the combined effect of salt (sodium chloride, 0–8% w/v), sorbate (potassium sorbate, 0–4.5% w/v), nisin (0–500 ppm) and lysozyme (0–500 ppm) on the survival of Clostridium sporogenes as a non‐toxigenic surrogate of Clostridium botulinum in terms of the probability of growth by using a central composite rotatable design. The results indicated that salt and sorbate were the most effective factors in preventing the growth of Cl. sporogenes in high‐moisture (>95%) and low‐acid conditions. The probability of growth of Cl. sporogenes in broth was reduced by combinations of salt and sorbate. Nisin and lysozyme had insignificant effects on the probability of growth of Cl. sporogenes (P > 0.05). Lysozyme individually and in combination with nisin had no inhibitory effect on Cl. sporogenes. Overall, the addition of sorbate and lysozyme may allow the salt concentration to be reduced while preventing growth.     

A Single Mutation at the Ferredoxin Binding Site of P450 Vdh Enables Efficient Biocatalytic Production of 25‐Hydroxyvitamin D3

Vitamin D₃ hydroxylase (Vdh) from Pseudonocardia autotrophica is a cytochrome P450 monooxygenase that catalyzes the two‐step hydroxylation of vitamin D₃ (VD₃) to produce 25‐hydroxyvitamin D₃ (25(OH)VD₃) and 1α,25‐dihydroxyvitamin D₃ (1α,25(OH)₂VD₃). These hydroxylated forms of VD₃ are useful as pharmaceuticals for the treatment of conditions associated with VD₃ deficiency and VD₃ metabolic disorder. Herein, we describe the creation of a highly active T107A mutant of Vdh by engineering the putative ferredoxin‐binding site. Crystallographic and kinetic analyses indicate that the T107A mutation results in conformational change from an open to a closed state, thereby increasing the binding affinity with ferredoxin. We also report the efficient biocatalytic synthesis of 25(OH)VD₃, a promising intermediate for the synthesis of various hydroxylated VD₃ derivatives, by using nisin‐treated Rhodococcus erythropolis cells containing Vdh_T107A. The gene‐expression cassette encoding Bacillus megaterium glucose dehydrogenase‐IV was inserted into the R. erythropolis chromosome and expressed to avoid exhaustion of NADH in a cytoplasm during bioconversion. As a result, approximately 573 μg mL^?1 25(OH)VD₃ was successfully produced by a 2 h bioconversion.     

Inactivation of spores of Bacillus cereus in cheese by high hydrostatic pressure with the addition of nisin or lysozyme

The objective of this work was to study high hydrostatic pressure (HHP) inactivation of spores of Bacillus cereus ATCC 9139 inoculated in model cheeses made of raw milk, together with the effects of the addition of nisin or lysozyme. The concentration of spores in model cheeses was approximately 6-log10 cfu/g of cheese. Cheeses were vacuum packed and stored at 8 degrees C. All samples except controls were submitted to a germination cycle of 60 MPa at 30 degrees C for 210 min, to a vegetative cells destruction cycle of 300 or 400 MPa at 30 degrees C for 15 min, or to both treatments. Bacillus cereus counts were measured 24 h and 15 d after HHP treatment. The combination of both cycles improved the efficiency of the whole treatment. When the second pressure-cycle was of 400 MPa, the highest inactivation (2.4 +/- 0.1 log10 cfu/g) was obtained with the presence of nisin (1.56 mg/L of milk), whereas lysozyme (22.4 mg/L of milk) did not increase sensitivity of the spores to HHP. For nisin (0.05 and 1.56 mg/L of milk), no significant differences were found between counts at 24 h and 15 d after treatment. Considering that mesophilic spore counts usually range from 2.6 to 3.0 log10 cfu/ml in raw milk, HHP at mild temperatures with the addition of nisin may be useful for improving safety and preservation of soft curd cheeses made from raw milk.     

Shelf‐life characteristics of fresh oysters and ground beef as affected by bacteriocin‐coated plastic packaging film

Fresh oysters and ground beef were wrapped in antimicrobial films coated with a bacteriocin (nisin or lacticin NK24) incorporated into a polyamide binder layer. The packaged foods were stored at 3 and 10 °C and changes in counts of total aerobic bacteria and coliform bacteria were monitored together with appropriate quality attributes in order to determine the influence of the bacteriocin‐coated films on quality preservation and shelf‐life extension. Compared to plain low‐density polyethylene film, plastic films with incorporated bacteriocins slowed down microbial growth on packaged oysters and ground beef at both temperatures, contributed in some degree to the preservation of chemical quality and extended shelf‐life significantly. The effects of the antimicrobial films on the suppression of coliform bacterial growth were more pronounced at 10 than at 3 °C , while the effects on total aerobic bacteria were consistently evident at both temperatures. There was no difference in food quality preservation between the two types of antimicrobial film. © 2002 Society of Chemical Industry     

Reduction of Brochothrix thermosphacta and Salmonella Serotype Typhimurium on Vacuum-Packaged Fresh Beef Treated with Nisin and Nisin Combined with EDTA

ABSTRACT: The effect of nisin and nisin/EDTA followed by vacuum packaging on the reduction of Brochothrix thermosphacta and Salmonella typhimurium counts on beef was investigated. Beef cubes, inoculated with either bacteria, were dipped in nisin, or nisin combined with EDTA solutions, vacuum packaged, and stored at 4 °C for up to 25 d. Growth of B. thermosphacta was completely inhibited by nisin and nisin/EDTA by up to 6.76 log₁₀ CFU/ml. However, neither treatment showed significant effects against S. Typhimurium. Thus, nisin or nisin/EDTA treatment, followed by vacuum packaging under refrigerated conditions could increase the shelf life of fresh beef by inhibiting the growth of B. thermosphacta , an important spoilage organism in beef.