Nisin: From a structural and meat preservation perspective.

Nisin is a posttranslationally modified antimicrobial peptide that is widely used as a food preservative. It contains five cyclic thioethers of varying sizes. Nisin activity and stability are closely related to its primary and three dimensional structures. It has nine reported natural variants. Nisin A is the most studied nisin as it was the first one purified. Here, we review the sequence feature of nisin A and its natural variants, and their biosynthesis pathway, mode of action and application as a meat preservative. We systematically illustrate the functional domains of the main enzymes (NisB, NisC, and NisP) involved in nisin synthesis. NisB was shown to dehydrate its substrate NisA via a tRNA associated glutamylation mechanism. NisC catalysed the cyclization of the didehydro amino acids with the neighboring cysteine residues. After cyclization, the leader peptide is removed by the protease NisP. According to multiple sequence alignments, we detected five conserved sites Dha5, Pro9, Gly14, Leu16, and Lys22. These residues are probably the structural and functional important ones that can be modified to produce peptides versions with enhanced antimicrobial activity. Through comparing various application methods of nisin in different meats, the antimicrobial effects of nisin used individually or in combination with other natural substances were clarified.

Sulfated exopolysaccharides from Porphyridium cruentum: A useful strategy to extend the shelf life of minced beef meat.

Sulfated exopolysaccharides (EPS) from Porphyridium cruentum strain were extracted and their antioxidant and anti-bacterial potentials were evaluated based on DPPH free radical, ABTS•+ radical cation and DNA nicking assays, and against four foodborne pathogenic bacteria, respectively. They showed also interesting functional, foaming and emulsion properties. Moreover, microbiological and chemical effects of EPS at 0.5, 1 and 2% on refrigerated minced beef meat were undertaken. Chemical analyses revealed that the treated meat underwent significant decrease (P < 0.05) of primary and secondary lipid oxidation. By the end of the storage period, exopolysaccharides at 2% reduced the metmyoglobin and carbonyl group accumulation compared to control samples and were more efficient (P < 0.05) against microflora proliferation. Furthermore, two multivariate exploratory techniques namely Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were applied successfully to all obtained data describing the main characteristics attributed to refrigerated meat samples. Overall, these findings indicated that EPS from P. cruentum are worthy being developed as functional and bioactive components for the meat industry.

Evaluation of the potential of protective cultures to extend the microbial shelf-life of chilled lamb meat.

The use of protective cultures to inhibit spoilage bacteria is a promising natural preservation technique to extend the shelf-life of fresh meat. This study evaluated the effectiveness of six food-grade protective cultures (containing different combinations of Lactobacillus sakei, Pediococcus pentosaceus, Staphylococcus xylosus, and Staphylococcus carnosus) on naturally contaminated chill-stored (4 °C) lamb meat in different packaging systems. Only slight reductions of common meat spoilage bacteria Brochothrix thermosphacta, Pseudomonas spp., and Enterobacteriaceae were observed in culture-treated samples stored in modified atmosphere packaging (80% O2:20% CO2). Greater inhibitory effects were found in vacuum-packed lamb, with mixed cultures containing either L. sakei, S. carnosus, and S. xylosus or S. carnosus and L. sakei causing the most significant reductions. Protective cultures did not adversely affect meat color or pH. This study demonstrated the potential of protective cultures comprising lactic acid bacteria and coagulase-negative staphylococci in controlling microbial spoilage of lamb and, by inference, other types of meat as a natural solution for shelf-life extension.