Polymer films releasing nisin and/or natamycin from polyvinyldichloride lacquer coating: Nisin and natamycin migration,efficiency in cheese packaging

Polyethylene films coated by commercially available polyvinyldichloride (PVdC) as well as nitrocellulose (NC) lacquer with addition of natamycin preparation Delvocid® (16.7% w/w of natamycin in lacquer) were studied at 6 and 23 °C to determine the preservative migration into distilled water. The films released natamycin at maximal level 2.34 ± 0.32 mg/dm². The diffusion coefficient of 0.79 × 10⁻¹⁰ ± 0.29 × 10⁻¹⁰ cm²/s and 1.03 × 10⁻¹⁰ ± 0.17 × 10⁻¹⁰ cm²/s was determined for natamycin transport in PVdC lacquer layer at 6 and 23 °C, respectively. For nitrocellulose lacquer the diffusion coefficient of 0.89 × 10⁻¹⁰ ± 0.16 × 10⁻¹⁰ cm²/s was found at 23 °C. The coextruded polyamide/polyethylene film coated with the PVdC lacquer containing both nisin (16.7% w/w of preparation Nisaplin®) and natamycin (see above) provided inhibitory effect against selected indicator microorganisms (Penicillium expansum, Fusarium culmorum, Lactobacillus helveticus, Listeria ivanovií). This film was unsuitable for the packaging of the surface ripened cheese Olomoucké tvar??ky. On the other hand, it was able to prevent the growth of spoilage microorganisms on the surface of the packaged soft cheese Bla?ácké zlato.     

冷却肉天然复合保鲜剂配比的优化

根据中心复合设计原理,在琼脂扩散法得出3 种天然保鲜剂最小抑菌浓度基础上,运用Minitab14 数据统计分析软件,采用四因素二水平中心复合响应曲面分析法,确定保鲜剂的最佳配比为Nisin 0.2773g/100mL、溶菌酶0.46g/100mL、乳铁蛋白0.604g/100mL、pH5.16。pH 值与乳铁蛋白、pH 值与溶菌酶、pH 值与Nisin、乳铁蛋白与溶菌酶以及溶菌酶与Nisin 之间均存在显著的交互作用(P＜ 0.01),而乳铁蛋白与Nisin 交互作用不显著(P＞0.05)。单因素对细菌总数影响的大小次序为Nisin ＞溶菌酶＞ pH 值＞乳铁蛋白。     

冷却肉生产中保鲜技术的研究——溶菌酶、Nisin、GNa液复合性保鲜试验

本试验详细研究了GNa液、乳酸菌肽(Nisin)、溶菌酶在冷却肉保鲜中的效果。试验得出GNa液对维持肉的感官指标具有良好的效果，Nisin对于抑制脂肪的酸败和G^ 细菌及大肠杆菌的增殖方面具有明显的效果，而溶菌酶对于控制细菌总数的增殖、减缓TVB—N值的上升方面具有极其重要的作用。在试验中由于采用了GNa液、Nisin、溶菌酶三者配合使用，取得了非常理想的效果，以第五组的保鲜效果最为理想。     

分割托盘小包装冷却肉溶菌酶、Nisin、GNa液保鲜试验研究

在溶菌酶、Nisin、GNa保鲜剂对托盘小包装冷却肉复合性保鲜的基础上,为取得更好的保鲜实验效果,进一步开展了溶菌酶、Nisin、GNa保鲜剂正交实验研究,以研究出能应用于生产实际的托盘包装冷却肉的有效保鲜剂。通过L9(34)正交试验,结果表明,三种保鲜剂经正交实验配合使用,对非真空托盘包装保鲜冷却肉的保鲜效果非常显著,使托盘包装保鲜的冷却肉在0～4℃条件下,有效保存时间达到24天以上。经正交实验研究后得出较优的工艺条件为A3B2C2D2,即GNa液采用5000ppm,Nisin2500ppm,溶菌酶2500ppm,用乳酸调pH值至4.5。     

Low-cost purification of nisin from milk whey to a highly active product

Nisin is a natural peptide used as a preservative in a variety of food products, in which it inhibits mainly Gram-positive bacterial growth, including multidrug-resistant pathogens. However, its application range depends on the cost-effective production and purification of this molecule. Our group has previously produced nisin by Lactococcus lactis cultivation in milk whey, which is an industrial residue from dairy production. To our knowledge, no report used milk whey as a culture medium, although several investigators have purified nisin using different techniques. We thus aimed to establish a low-cost purification of nisin obtained by this process. Samples were diluted in ammonium sulphate, applied onto HIC columns (butyl sepharose CL 4B matrix), and eluted with Milli-Q water or PBS. Elution fractions were monitored for protein content and nisin antibacterial activity. Water elution resulted in purification factor values (270, commercial nisin; 775, nisin produced in-house) higher than those obtained with PBS elution. We concluded that purification of nisin does not require precipitation with ammonium sulphate, therefore allowing step/cost reduction. Moreover, purification from milk whey using HIC provides nisin with high activity and low salt content, which can further be applied to a variety of areas.     

Nutritional factors affecting the production of two bacteriocins from lactic acid bacteria on whey

The ability of Lactococcus lactis subsp. lactis CECT 539 and Pediococcus acidilactici NRRL B-5627 to produce bacteriocins on both diluted and concentrated whey was investigated in batch fermentations. Both strains produced the higher amounts of biomass and bacteriocin titres on diluted whey. Luedeking and Piret expression was able to model the production of nisin, which was produced as a primary metabolite on both culture media. However, the pediocin production could not be typified in any case due to the negligible growth of P. acidilactici. Although the whey supported the growth and bacteriocin production by the two strains, both biomass and bacteriocin productions were lower than those obtained on MRS broth. The effect of total sugar, nitrogen, phosphorous and buffer concentrations on the production of nisin and pediocin was studied in diluted whey using factorial experiments and empirical modelling. The production of nisin was greatly inhibited by the increase in nitrogen, buffer, and to a lesser extent, sugar concentration in the medium, nevertheless, the used phosphorous source produced a light stimulatory effect on bacteriocin synthesis. In addition, the growth of Lc 1.04 was mainly affected by the nitrogen source used. On the other hand, pediocin was inhibited by the increase in buffer, phosphorous, and to a lesser degree, by the sugar and nitrogen concentration.

The inhibitory activity of pediocin disappeared almost totally after 15 min of treatment with trypsin, papain, subtilisin and pepsin. The activity of nisin was drastically reduced by treatment with trypsin, subtilisin and pepsin. Nevertheless, 50% of the initial activity was retained when nisin was treated with papain. Both bacteriocins showed the highest heat stability at acidic pH and short incubation times.     

High nisin-Z production during repeated-cycle batch cultures in supplemented whey permeate using immobilized Lactococcus lactis UL719

Nisin-Z production was studied during repeated-cycle pH-controlled batch (RCB) cultures using Lactococcus lactis subsp. lactis biovar. diacetylactis UL719 immobilized in κ-carrageenan/locust bean gum gel beads in supplemented whey permeate. After an initial colonization of gel beads during the first two cycles, nisin-Z production in bulk medium and gel beads was very similar for 1-h and 2-h cycle RCB cultures. A very high nisin-Z production (8200 IU mL⁻¹) was measured in the broth after the 1-h cycles, with a corresponding volumetric productivity of 5730 IU mL⁻¹ h⁻¹. This productivity is much higher than maximum nisin productivities reported in literature or maximum productivities obtained previously for free-cell batch cultures (850 IU mL⁻¹ h⁻¹), and free-cell (460 IU mL⁻¹ h⁻¹) or immobilized-cell (1760 IU mL⁻¹ h⁻¹) continuous cultures, using the same strain and fermentation conditions. The stability of RCB cultures was demonstrated for 24 and 36 1-h cycles carried out over 3 and 6-day periods, respectively. Changing environmental conditions during batch cultures resulted high nisin production.     

Nisin在干酪保藏中的应用

讨论了Nisin在干酪的保藏、加工、贮存过程中的变化,并以Nisin在Chedder和天然干酪为例探讨了Nisin的应用的保藏效果。     

三种保鲜剂的比较试验

本课题进行了GNa液、溶菌酶、Nisin单一因子对冷却肉保鲜效果的比较试验研究.结果表明,当三种保鲜剂单独使用时,溶菌酶的保鲜效果极明显地优于对照组,也显著地优于GNa液组,略优于Nisin组.     

Effects of combined exposure of Micrococcus luteus to nisin and pulsed electric fields

Death and injury following exposure of Micrococcus luteus to nisin and pulsed electric field (PEF) treatment were investigated in phosphate buffer (pH 6.8, σ=4.8 ms/cm at 20°C). Four types of experiment were carried out, a single treatment with nisin (100 IU/ml at 20°C for 2 h), a single PEF treatment, a PEF treatment followed by incubation with nisin (as before) and addition of nisin to the bacterial suspension prior to the PEF treatment. The application of nisin clearly enhanced the lethal effect of PEF treatment. The bactericidal effect of nisin reduced viable counts by 1.4 log₁₀ units. Treatment with PEF (50 pulses at 33 kV/cm) resulted in a reduction of 2.4 log₁₀ units. PEF treatment followed by nisin caused a reduction of 5.2 log₁₀ units in comparison with a 4.9 log₁₀ units reduction obtained with nisin followed by PEF. Injury of surviving cells was investigated using media with different concentrations of salt. Sublethally damaged cells of M. luteus could not be detected by this means, following PEF treatment.