Listeria monocytogenes is a Gram positive, aerobic, facultative anaerobic and nonacid fast bacterium, which can cause the disease listeriosis in both human and animals. It is widely distributed thoroughout the environment and has been isolated from various plant and animal food products associated with listeriosis outbreaks.

Contaminated ready-to-eat food products such as gravad and cold-smoked salmon and rainbow trout have been associated with human listeriosis in Sweden. The aim of this study was to analyse the occurrence and level of L. monocytogenes in
gravad and cold-smoked salmon (Salmo salar) products packed under vacuum or modified atmosphere from retail outlets in Sweden. Isolated strains were characterized by serotyping and the diversity of the strains within and between
producers were determined with PFGE (Pulsed-field gel electrophoresis). The characterized fish isolates were compared with previously characterized human strains.
L. monocytogenes was isolated from 11 (three manufacturers) of 56 products analysed. This included gravad salmon products from three manufacturers and cold-smoked salmon from one manufacturer. The highest level of L. monocytogenes found was 1500 cfu/g from a cold-smoked salmon product but the level was low (<100 cfu/g) in most of the products. Serovar 1/2a was predominant,
followed by 4b. Three products of gravad salmon harboured more than one serovar. PFGE typing of the 56 salmon isolates detected five Asc I types: four types were identical to human clinical strains with Asc I and one was identical and one was closely related to human clinical strains with Apa I. Isolation of identical or closely related L. monocytogenes strains from human clinical cases of listeriosis and gravad and cold-smoked salmon suggested that these kinds of products are possible sources of listeriosis in Sweden. Therefore, these products should be considered risk products for human listeriosis.

Listeria monocytogenes, a food-borne pathogen

Essential oils as antimicrobials in food systems – A review

Myoglobin and lipid oxidation interactions: mechanistic bases and control

Antimicrobials are classified as traditional when they (i) have been used for many years, (ii) are approved by many countries for inclusion as antimicrobials in foods (e.g., lysozyme and lactoferrin, which are naturally occurring but regulatory-agency approved), or (iii) are produced by synthetic means (as opposed to natural extracts). Many organic acids are used as food additives, but not all have antimicrobial activity. Research suggests that the most active are acetic, lactic, propionic, sorbic, and benzoic acids. Acetic acid was the most effective antimicrobial in ground roasted beef slurries against Escherichia coli O157:H7 growth in comparison with citric or lactic acid. Sorbate is applied to foods by direct addition, dipping, spraying, dusting, or incorporation into packaging. The mechanism by which dimethyl dicarbonate (DMDC) acts is most likely related to inactivation of enzymes. A related compound, diethyl dicarbonate, reacts with imidazole groups, amines, or thiols of proteins. Lysozyme is most active against gram-positive bacteria, most likely because the peptidoglycan of the cell wall is more exposed. The primary use for sodium nitrite as an antimicrobial is to inhibit Clostridium botulinum growth and toxin production in cured meats. Sulfites may be used to inhibit acetic acid-producing bacteria, lactic acid bacteria, and spoilage bacteria in meat products. In the future, traditional food antimicrobials will continue to play an important role in food preservation.

Chemical Preservatives and Natural Antimicrobial Compounds

Healthier meat and meat products: their role as functional foods.

Low-fat meat products-technological problems with processing.

Alternatives to antibiotics: chemical and physical antimicrobial interventions and foodborne pathogen response

Properties of low-fat (<18%) frankfurters containing high-oleic acid sunflower oil (HOSO) and fish oil were studied. Replacement of animal fats by the oils had little effect on emulsion stability. Frankfurters with 5% fish oil had very low sensory scores due to undesirable fish flavor. Incorporation of maximum amounts of HOSO into low-fat beef/pork and all-beef frankfurters increased oleic acid by 34% and 62%, respectively, and the monounsaturated/saturated fatty acid ratio by 178% and 468%, respectively, compared to a regular (30% fat) product containing only animal fats. Sensory evaluation and instrumental texture profile analysis showed that the reduction in total fat caused texture problems, especially increased firmness and springiness and decreased juiciness.

Jimmy T. Keeton

Papers

Low-fat meat products-technological problems with processing.

Alternatives to antibiotics: chemical and physical antimicrobial interventions and foodborne pathogen response

Properties of Low‐Fat Frankfurters Containing Monounsaturated and Omega‐3 Polyunsaturated Oils

Antioxidant properties of plum concentrates and powder in precooked roast beef to reduce lipid oxidation.

Utilization of soy protein isolate and konjac blends in a low-fat bologna (model system)