Nisin composition

Recent results indicate that not only topogenic signals and membrane composition contribute to the proper topology of a membrane protein. The antimicrobial peptide nisin, produced by Lactococcus lactis, kills Gram-positive bacteria via pore formation, thus leading to the permeabilisation of the membrane. Nisin depends on the cell-wall precursor Lipid II, which functions as a docking molecule to support a perpendicular stable transmembrane orientation [43]. 

The inability to obtain complete protein sequence analysis of purified bacteriocins has been reason to suspect the presence of N-blocked peptide sequences (34) or lantibiotic residues (14). Recently, Piard et al. (14) have shown from partial sequencing and composition analysis that lacticin 481, a broad spectrum bacteriocin produced by L. lactis 481, also contains lanthionine residues. The early widespread interest in nisin and nisin-producing strains had given the impression that lantibiotics may be characteristic of bacteriocins of lactic acid bacteria. However, recent studies with other LAB bacteriocins suggest that simple peptide bacteriocins may prevail among the LAB. 

Central Composite Design of Factors in Coded Levels with Nisin and Lactic Acid Concentration as Response... 

In the second optimization step, the exact values of the three variables that were identified to have significant effects on nisin and/or lactic acid production were determined using a central composite design (Table 2). The coded and actual values of each variable are given in Table 3. The fermentation media (pH 6.5) were composed of 50 g/L of whey, 5 g/L of polypeptone, 1 g/L of Tween-80, and 30 g/L of CaC03, and the predetermined amount of the three variables was assigned by the central composite design. The content of nisin and lactic acid after 24 h of fermentation at 30°C was measured and are presented as responses in Table 2. 

Nisin Lactococcus lactis IOA IULA A+PGA+KA+ GALMGA+NMKA+AA+ A+HA+HVUK Unusual amino acid composition Inactive 2 (56-58)... 

Elevated temperature and citric acid have been found to increase the susceptibility to nisin, both in culture and in foods. Exposure to a temperature of 60°C for 10 min, followed by 24 h incubation by 30°C showed no survival of bacterial cells. However, at a temperature of 50°C some viable cells were found with the application of nisin, but survivor numbers were significantly reduced. Stationary phase cells are more resistant to both organic acids alone, as well as in combination with nisin, than log-phase cells. It is speculated that Gram-negative bacterial cells are protected from the effects of nisin by the composition of their outer layers. When these are weakened by elevated temperature, they become sensitive by similar mechanisms as Gram-positive bacteria (Phillips and Duggan, 2002). 

Antimicrobial Edible films were prepared from natural fiber of pectin and other food hydrocolloids for food packaging or wrapping by extrusion followed by compression or blown film method. Microscopic analysis revealed a well mixed integrated structure of extruded pellets and an even distribution of the synthetic hydrocolloid in the biopolymers. The resultant composite films possess the mechanical properties that are comparable to films cast from most natural hydrocolloids that consumed as foods or components in processed foods. The inclusion of polyethylene oxide) alters the textures of the resultant composite films and therefore, demonstrating a new technique for the modification of film properties. The composite films were produced in mild processing conditions, thus, the films are able to protect the bioactivity of the incorporated nisin, as shown by the inhibition of Listeria monocytogenes bacterial growth by a liquid incubation method. 

The class IA lantibiotic nisin was shown to form ion-permeable channels in the cytoplasmic membrane of susceptible cells, resulting in an increase in the membrane permeabiHty, distmbing the membrane potential and causing an efflux of ATP, amino acids, and essential ions such as potassiiun and magnesium. Ultimately, the biosynthesis of macromolecules and energy production are inhibited resulting in cell death. Nisin does not require a membrane receptor but requires an energized membrane for its activity, which appeared to be dependent on the phospholipid composition of the membrane [67]. 

Nisin was also incorporated by diffusion into a pectin/PLA biopolymer composite by extrusion. The previously extmded pectin and PLA composite... 

Verheul, A., Russell, N.J., VantHof, R., et al. (1997). Modifications of membrane phospholipid composition in nisin-resistant Listeria manacytagenes Scott A. Appl Enviran Micrabial 63, 3451-3457. 

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