Impedance measurement of growth of lactic acid bacteria in the presence of nisin and lysozyme

Effect of nisin (0.500 g/l), lysozyme (0.035 g/l) and the mix of nisin (0.500 g/l) and lysozyme (0.035 g/l) against two nisin-producing lactococci strains, three non-nisin-producing lactococci strains and four lactobacilli strains with antimicrobial activity was determined by the impedimetric method. None of the tested lactococci and lactobacilli strains were inhibited by lysozyme at concentration of 0.035 g/l. Only the nisin-producing lactococci strains were resistant to nisin at 0.500 g/l, the other lactococci and lactobacilli were inhibited by nisin at 0.500 g/l intensively. The mix of lysozyme and nisin displayed a comparable effect to the nisin addition against the used lactococci strains and was very variable depending on the strain of tested lactobacilli. The impedimetric method was shown to be convenient for screening the growth abilities of lactococci and lactobacilli in the presence of antimicrobial components.     

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.     

食品中Nisin抗菌效果影响因素的研究

研究了木瓜蛋白酶的添加量、Nisin的添加量及 p H对 Nisin抗菌效果的影响。得出了处理后细菌数和各因素间的二次回归方程 :y=30 .44- 1 8.74x1 1 6.52 x- 4.36x3- 1 8.2 x1x2 1 8.1 0 x     

Identification of Clostridium butyricum as the bacteria causing soy sauce explosion and leakage and its control using nisin

The cause of leakage and explosion of bottled soy sauce was determined by isolating gas-forming bacteria from leaking soy sauce samples, and identifying them as Clostridium butyricum. This is the first report of the isolation of C. butyricum from bottled soy sauce and identification of gas production by the bacteria as the cause of swelling and leakage in soy sauce. Their gas production was further confirmed by inoculating uncontaminated soy sauce with the C. butyricum isolated from a leaking bottle of soy sauce. The source of C. butyricum contamination could be traced back to the ingredient monosodium glutamate (MSG) with C. butyricum spores. Nisin (50 mg/L) was successfully employed to prevent C. butyricum from spoilage. The incidence of leakage of bottled soy sauce was markedly reduced after 50 mg/L nisin was added. The isolation and identification work assist food industry to control the leakage of soy sauce, and the strategy utilized in this work should assist in the characterization of spoilage organisms in other food systems.     

The use of rosemary extract in combination with nisin to extend the shelf life of pompano (Trachinotus ovatus) fillet during chilled storage

The effects of rosemary extract (RE) combined with nisin (N) on the quality of pompano (Trachinotus ovatus) were assessed throughout 15 days of storage at 4 ± 1 °C. Physicochemical (peroxide value, thiobarbituric acid, total volatile basic nitrogen, trimethylamine, pH, K value, texture, and color), sensory, and bacteriological characteristics of fish fillet were all periodically analyzed. RE + N treatment effectively improved physicochemical quality parameters and the sensory, and reduced microbial growth as compared with either treatment of RE or N alone or the control, which resulted in a significant extension in the shelf life of pompano fillet. Therefore, rosemary extract combined with nisin treatment may be a promising method of maintaining the storage quality and extending shelf life of pompano fillet during chilled storage.     

In vitro release kinetics of nisin as affected by Tween 20 and glycerol co-encapsulated in spray-dried zein capsules

Delivery systems with sustained release of antimicrobials have been proposed to improve long-term effectiveness of antimicrobials in foods. In this work, we studied the effect of Tween 20 and glycerol in spray-drying formulations on resultant microstructures of zein capsules and release profiles of encapsulated nisin. Tween 20 and glycerol changed capsules from a continuous matrix to shell-type structures. All samples showed complete release of nisin in 30 min at pH 2.0. Capsules with a higher amount of Tween 20 showed more complete release of nisin at pH 8.0, in contrast to no apparent impact by glycerol. Addition of 0.05% Tween 20 or glycerol in the feed both reduced the burst release of nisin at pH 6.0, but no conclusive trends were observed for the impact of their usage levels. Our work showed that an appropriate formulation is needed to obtain desirable delivery systems of antimicrobials such as nisin.