Novel combinations of chitosan, carnocin and sulphite for the preservation of chilled pork sausages.

The aim of this study was to develop novel preservation systems for fresh pork sausages based on combinations of chitosan (polymeric ß-1,4-N-acetylglucosamine) carnocin (a bacteriocin produced by Carnobacterium piscicola) and low concentrations of sulphite. Two pilot-scale trials showed that 0.6% chitosan combined with low sulphite (170 ppm) retarded the growth of spoilage organisms more effectively (3-4 log cfu/g) than high levels (340 ppm) of sulphite alone at 4 °C for up to 24 days. Microbial counts for frozen sausages showed that the preservative efficacy of the chitosan/sulphite combination was maintained following frozen storage. Carnocin did not protect sausages from spoilage but in a challenge trial, it reduced the numbers of Listeria innocua by up to 2.0 log cfu/g in the first 5 days of chill-storage. Sulphite was degraded rapidly within the first 3 days of storage in all the sausages that contained only this preservative but levels decreased less rapidly and persisted for longer in the presence of chitosan. Results of Quantitative Descriptive Analysis using 31 trained panellists reflected the gradual deterioration of all the sausages during storage. The batch containing chitosan and sulphite deteriorated less rapidly and was judged to be more acceptable for a longer period than all the other batches.

Food fermentations: role of microorganisms in food production and preservation.

Preservation of foods by fermentation is a widely practiced and ancient technology. Fermentation ensures not only increased shelf life and microbiological safety of a food but also may also make some foods more digestible and in the case of cassava fermentation reduces toxicity of the substrate. Lactic acid bacteria because of their unique metabolic characteristics are involved in many fermentation processes of milk, meats, cereals and vegetables. Although many fermentations are traditionally dependent on inoculation from a previous batch starter cultures are available for many commercial processes such as cheese manufacture thus ensuring consistency of process and product quality. This review outlines the role of lactic acid bacteria in many such fermentations and the mechanisms of antibiosis with particular reference to bacteriocins and gives a brief description of some important fermented foods from various countries. It is anticipated that the contribution of the advances in lactic acid bacteria research towards improvement of strains for use in food fermentation will benefit both the consumer and the producer.

Isolation from food sources, of lactic acid bacteria that produced antimicrobials.

The potential of lactic acid bacteria, isolated from a variety of foods, to inhibit indicators representative of spoilage and pathogenic bacteria associated with food products was examined. Fruit and vegetables were a poor source of lactic acid bacteria but large numbers were readily isolated on MRS agar from cheese, milk and meat samples. Approximately 1000 isolates from each of the food samples were examined by the deferred antagonism procedure to determine their ability to inhibit Staphylococcus aureus, Listeria innocua and Pseudomonas fragi. Listeria innocua was the bacterium predominantly inhibited by isolates from the cheese, milk and meats, but antagonism was also observed to a lesser extent against the other indicators. The only inhibition observed for isolates from vegetable material was directed against Staph. aureus. The majority of inhibitor producers were effective against only one of the indicators but a small number were isolated which inhibited two or three.

pAMbeta1-Associated Mobilization of Proteinase Plasmids from Lactococcus lactis subsp. lactis UC317 and L. lactis subsp. cremoris UC205.

A combination of plasmid curing and DNA-DNA hybridization data facilitated the identification of proteinase plasmids of 75 (pCI301) and 35 kilobases (pCI203) in the multi-plasmid-containing strains Lactococcus lactis subsp. lactis UC317 and L. lactis subsp. cremoris UC205, respectively. Both plasmids were transferred by conjugation to a plasmid-free background only after introduction of the conjugative streptococcal plasmid, pAMbeta1. All Prt transconjugants from matings involving either donor contained enlarged recombinant Prt plasmids. UC317-derived transconjugants were separable into different classes based on the presence of differently sized cointegrate plasmids and on segregation of the pCI301-derived Lac and Prt markers. All UC205-derived transconjugants harbored a single enlarged plasmid that was a cointegrate between pCI203 and pAMbeta1. The identification of prt genes on pCI301 and pCI203 derivatives was achieved by a combination of restriction enzyme and hybridization analyses.