A fast micromethod for the estimation of nisin activity in a soft cheese
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The British Standard protocol currently used to determine the nisin concentration in cheese requires the manipulation of a 40 g sample involves two critical points, pH adjustment and heating/cooling. In this work, we developed a fast micromethod that permits the manipulation of 0.2 g cheese, substitutes the use of 0.02N HC l by 50 mM citric acid and facilitates the handling of many samples in reduced time, and with increased efficiency/yield. This change keeps the pH stable at ~3.4, enough to sidestep the pH adjustment, and nisin antimicrobial activity was stable at boiling temperatures.The pentacyclic peptide antibiotic nisin, produced by Lactococcus lactis is ubiquitously applied as a food preservative. We previously demonstrated that the truncated nisin-(1-22) has only 10-fold lower activity than nisin. Here we aimed at further developing this tricyclic nisin analog to reach activity comparable to that of nisin. Our data demonstrate that: (1) ring A has a large mutational freedom; (2) the composition of residues 20–22 strongly affects production levels of nisin-(1-22); (3) a positively charged C-terminus of nisin-(1-22) significantly enhances its antimicrobial activity; (4) nisin-(1-22) inhibits in vitro growth of a target strain using different dynamics than nisin.
Lantibiotics
Lipid II
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Autoclave
Food Preservatives
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A nisin-resistant strain of Pectinatus frisingensis (Nis-5000) to high nisin concentration (5000 IU ml−:1) was isolated. The nisin resistance phenotype of strain Nis-5000 was stable after five passages through nisin-free medium. The involvement of the cell envelope in nisin resistance was investigated. EDTA treatment of Nis-5000 strain cells did not render them sensitive to the bacteriocin, suggesting that the lipopolysaccharide layer was not involved in nisin resistance. The Nis-5000 strain shows a significantly different fatty acid composition compared with that of the wild-type strain. The modifications occurred mainly in C17:1 (P<0.05) and C18:cyclo (P<0.05), suggesting the involvement of membrane fluidity in preventing nisin's effect.
Cell envelope
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Lipid II
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Aims: The following polymers were developed: polyethylene (PE), a PE and polyethylene oxide (70% PE and 30% PEO; PE + PEO) blend, PE and nisin (PE + nisin), PE, nisin, and EDTA (PE + nisin + EDTA), and PE + PEO with nisin (PE + PEO + nisin). Methods and Results: Of the polymers tested, PE and PE + PEO did not exhibit any antimicrobial activity against Brochothrix thermosphacta (BT); however, PE + nisin, PE + nisin + EDTA, and PE + PEO + nisin did. Beef surfaces were experimentally inoculated with 3·50 log10 cfu/cm2 of BT, vacuum packaged with each of the five polymers, and held at 4°C for 21 d. After 3 d at 4°C, BT was reduced > 1·70 log10 by PE + nisin and > 3·50 log10 with PE + nisin + EDTA or PE + PEO + nisin. By 21 d at 4°C, BT was reduced to 0·30 log10 cfu/cm2 when treated with PE + PEO + nisin. Conclusions: It appears that PE + PEO + nisin or PE + nisin + EDTA were more effective for reducing BT, as compared to polymers composed of PE + nisin. Significance and Impact of the Study: Nisin‐incorporated polymers may control the growth of undesirable bacteria, thereby extending the shelf life and possibly enhancing the microbial safety of meats.
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The effect of combinations of nisin and ethanol on the survival of Listeria monocytogenes was investigated.Killing by nisin was enhanced during simultaneous exposure to ethanol (2-7% v/v). For example, while 10 IU ml(-1) nisin reduced viability by 1 log unit in 20 min, a combination of this antimicrobial peptide and 5% ethanol, reduced numbers of surviving cells by 3 log units. Increasing the concentrations of either ethanol (2-7%) or nisin (10-50 IU ml(-1)) led to increased cell death with synergy being demonstrated for all combinations tested and at a range of temperatures from 5 to 37 degrees C.Ethanol can act synergistically with nisin to reduce the survival of L. monocytogenes.Combinations of ethanol and nisin may be feasible as an effective way of controlling this pathogen in the food processing environment.
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Isolation and characterisation of two degradation products derived from the peptide antibiotic nisin
Two degradation products of nisin have been isolated and their structures have been determined by 1 H NMR. Nisin 1–32 [(des‐ΔAla33‐Lys34; Val32‐NH 2 )nisin] and (des‐ΔAla5)nisin 1–32 [(des‐ΔAla5, ΔAla33‐Lys34; Ile4‐NH 2 , pyruvyl‐Leu6, Val32‐NH 2 )nisin] are formed on storage or by acid treatment. Contrary to previous reports, nisin 1–32 showed potent antimicrobial activity against Gram‐positive organisms comparable to that of nisin itself. (des‐ΔAla5)Nisin 1–32 , however, was biologically inactive, thus demonstrating the importance of ΔAla5 and/or ring A for biological activity.
Isolation
Lantibiotics
Degradation
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Lantibiotics
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The objective of this study was evaluating the effectiveness of encapsulated nisin in liposoms in contrast to free nisin in control of Listeria monocytogenes ATCC 19117 in Feta cheese during its ripening. The size of the nano-encapsules with nisin was around 103-150 nm and of the nano-encapsules without nisin was of approximately 101-143 nm. Addition of 500IU/g nisin to cheese resulted into 0.57, 4 and 3.7 log reduction in viable cells, respectively in free nisin, nano-encapsulated nisin (formulation 1) and nano-encapsulated nisin (formulation 2) at the end of four weeks ripening. In addition, changes in pH during this period of time was also affected by the form of addition of nisin, it was significantly different from liposomal nisin formulations(p<0.01). Since the free nisin had negative effect on starters, pH of this treatment could not achieve the standard range of pH determined for feta cheese and deficiencies in quality was observed.
Keywords: Feta, Listeria, Nisin, Nano-Encapsulation
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