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

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

References.- 1 Solubility of Proteins.- 1.1 Introduction.- 1.1.1 Factors Affecting Solubility of Proteins.- 1.2 Solubility of Meat and Fish Proteins.- 1.2.1 Solubility of Muscle Proteins.- 1.2.2 Solubility of Stroma Proteins.- 1.2.3 Protein Solubility in Processed Meats.- 1.2.4 Solubility of Blood Proteins.- 1.2.5 The Effect of Heating on Solubility of Proteins.- 1.2.6 The Effect of Freezing and Storage When Frozen on Protein Solubility.- 1.2.7 The Effect of Protein Modification and Irradiation Treatment.- 1.3 Solubility of Milk Proteins.- 1.4 Solubility of Egg Proteins.- 1.5 Solubility of Plant Proteins.- 1.5.1 Soybean Proteins.- 1.5.2 Peanut Proteins.- 1.5.3 Pea and Bean Proteins.- 1.5.4 Sunflower Proteins.- 1.5.5 Corn Proteins.- 1.5.6 Miscellaneous Plant Proteins.- References.- 2 Water Holding Capacity of Proteins.- 2.1 Introduction.- 2.2 The Mechanism of Protein-Water Interaction.- 2.2.1 Factors Influencing Water Binding of Proteins.- 2.3 Water Holding Capacity of Proteins in Meat and Meat Products.- 2.3.1 Water Binding Capacity of Muscle Proteins.- 2.3.2 Factors Influencing Water Binding of Muscle Proteins.- 2.3.3 Water Binding in Comminuted Meat Products.- 2.3.4 Milk Proteins in Comminuted Meats.- 2.3.5 Soy Proteins in Comminuted Meats.- 2.3.6 Corn Germ Protein in Comminuted Meats.- 2.4 Water Holding Capacity of Milk Proteins.- 2.5 Water Holding Capacity of Egg Proteins.- 2.6 Water Holding Capacity of Plant Proteins.- 2.6.1 Soybean Proteins.- 2.6.2 Pea and Bean Proteins.- 2.6.3 Sunflower Proteins.- 2.6.4 Corn Proteins.- 2.6.5 Wheat Proteins.- 2.6.6 Miscellaneous Proteins.- References.- 3 Emulsifying Properties of Proteins.- 3.1 Introduction.- 3.2 Hydrophobic and Hydrophilic Properties of Proteins.- 3.3 Interfacial Film Formation and Properties.- 3.4 Factors Affecting the Emulsifying Properties of Proteins.- 3.4.1 Protein Concentration.- 3.4.2 pH of Medium.- 3.4.3 Ionic Strength.- 3.4.4 Heat Treatment and Other Factors.- 3.5 Emulsion Stability.- 3.6 Measuring Emulsifying Properties.- 3.7 Emulsifying Properties of Meat Proteins and Proteins Utilized as Extenders in Meat Products.- 3.7.1 Protein Functionality in Comminuted Meats.- 3.7.2 Emulsifying Properties of Various Muscular Proteins.- 3.7.3 Emulsifying Properties of Blood Proteins.- 3.8 Functionality of Nonmeat Proteins in Comminuted Meats.- 3.8.1 Milk Proteins.- 3.8.2 Soy Proteins.- 3.8.3 Corn and Wheat Germ Proteins.- 3.9 Milk Proteins as Emulsifiers in Food Systems.- 3.9.1 Emulsifying Properties of Caseins and Caseinates.- 3.9.2 Emulsifying Properties of Whey Proteins.- 3.10 Emulsifying Properties of Egg Proteins.- 3.11 Emulsifying Properties of Plant Proteins.- 3.11.1 Soybean Proteins.- 3.11.2 Pea and Bean Proteins.- 3.11.3 Corn Proteins.- 3.11.4 Miscellaneous Proteins.- References.- 4 Oil and Fat Binding Properties Of Proteins.- 4.1 Introduction.- 4.2 Fat Binding Properties of Proteins of Animal Origin.- 4.2.1 Muscle Proteins.- 4.2.2 Soy Proteins in Comminuted Meats.- 4.2.3 The Effect of Corn Germ Protein Flour on Fat Binding in Ground Beef Patties.- 4.2.4 Milk and Egg Proteins.- 4.3 Fat Binding Properties of Proteins of Plant Origin.- 4.3.1 Soy Proteins.- 4.3.2 Pea, Bean and Guar Proteins.- 4.3.3 Corn Germ Proteins.- 4.3.4 Wheat Proteins.- 4.3.5 Cottonseed Proteins.- 4.3.6 Miscellaneous Proteins.- References.- 5 Foaming Properties of Proteins.- 5.1 Introduction.- 5.2 The Mechanism of Foam Formation.- 5.2.1 Factors Affecting Foam Formation.- 5.2.2 Foam Stability.- 5.3 Milk Proteins.- 5.3.1 Factors Affecting the Foaming Properties of Milk Proteins.- 5.4 Egg Proteins.- 5.4.1 The Effect of Processing on Foaming Properties of Egg Proteins.- 5.5 Blood Proteins and Gelatin.- 5.6 The Foaming Properties of Plant Proteins.- References.- 6 Gelling Properties of Proteins.- 6.1 Introduction.- 6.2 The Mechanism of Protein Gel Formation.- 6.2.1 Heat-Induced Gelation.- 6.2.2 Protein-Water Interaction in Gels.- 6.2.3 Factors Affecting the Properties of Gels.- 6.3 Gelling Properties of Meat Proteins.- 6.3.1 Myofibrillar Proteins.- 6.3.2 Sarcoplasmic Proteins.- 6.3.3 Gelation of Red and White Muscle Proteins.- 6.3.4 Factors Affecting the Gelling Properties of Meat Proteins.- 6.3.5 Myosin Blends with Other Proteins and Lipids.- 6.3.6 Fish Proteins.- 6.3.7 Collagen Gelation.- 6.3.8 Blood Proteins.- 6.4 Gelling Properties of Milk Proteins.- 6.4.1 Gelling Properties of Whey Protein Concentrate, Isolate, and Individual hey Proteins.- 6.4.2 The Effect of Heating and Protein Concentration.- 6.4.3 Gelation of Casein.- 6.4.4 Factors Affecting the Gelling Properties of Milk Proteins.- 6.5 Gelling Properties of Egg Proteins.- 6.5.1 Gelation of Egg White.- 6.5.2 Gelation of Yolk.- 6.6 Gelling Properties of Soy Proteins.- References.

Functionality of Proteins in Food

Disruption of Escherichia coli, Listeria monocytogenes and Lactobacillus sakei cellular membranes by plant oil aromatics

Stress, sublethal injury, resuscitation, and virulence of bacterial foodborne pathogens.

Frankfurter quality was monitored to evaluate effects of frozen storage on meat components. After fresh meat controls were tested, beef, pork, and pork fat were frozen and stored at −17.8°C for 1–37 wk. At 6-wk intervals, functional and quality tests were performed on thawed and control meat samples and on frankfurters made from the samples. Frozen storage significantly affected beef and pork lean (drip loss, % solids and N in drip, extractable protein, water binding, emulsifying capacity) and fat (beef-thiobarbituric acid and pork-peroxide values); frankfurters produced from these ingredients were also affected (cooking tests, penetration force, sensory panel scores).

Effects of frozen storage on functionality of meat for processing

Methylxanthines and related compounds were added to Duncan-Strong (DS) medium in an effort to improve spore yields and enterotoxin production in three strains of Clostridium perfringens. Supplementation with 50–200 μg of caffeine/ml (0.26–1.03 mM) increased heat-resistant spore yields for strain NCTC 8238 from 4.32 to 6.03 log10 spores/ml after 24 h of incubation. With strains NCTC 8239 and NCTC 10240, 50–200 μg/ml caffeine (0.26–1.03 mM) or theophylline (0.28–1.11 mM) were equally effective, and increased spore yields from 4.18–4.89 to 6.00–7.13 log10 spores/ml. When sporulation and enterotoxin production were evaluated in DS medium containing either starch or raffinose and supplemented with 100 μg/ml caffeine, heat-resistant spores were first detected at 6 h, and enterotoxin at 3 h of incubation. Raffinose not only yielded higher spore numbers than starch, but also shortened the time to toxin detection and/or increased toxin production by two out of three strains. Strain NCTC 8238 produced enterotoxin (2 ng/ml) with raffinose within 3 h, while strain NCTC 10240 produced 2 ng/ml enterotoxin with starch and higher levels (4 ng/ml) with raffinose at 3 h. In contrast, strain NCTC 8239 produced enterotoxin (2 ng/ml) at 3 h only with starch.

Evaluation of methylxanthines and related compounds to enhance clostridium perfringens sporulation using a modified duncan and strong medium

Antibotulinal properties of selected aromatic and aliphatic aldehydes

Combined water activity and solute effects on growth and survival of Listeria monocytogenes Scott A

Caffeic acid (CA) is widely distributed among higher fruits and vegetables. While CA has antimicrobial activity, little information exists on its utility as a food additive. As such, CA was tested for activity against Clostridium botulinum spores. At 0.78 and 3.25 mM, CA inhibited germination for 6 and 24 hr, respectively, with > 100 mM required to render spores nonviable. CA concentrations greater than or equal to 50 mM reduced 80 degrees C spore thermal resistance. Sporostatic activity was retained when tested in commercial meat broths, and 5.0 mM CA delayed toxigenesis. Caffeic acid has potential as a food additive to inhibit growth of C. botulinum, and reduce thermal processing requirements of heat sensitive foods.

Arthur J. Miller

Papers

Effects of frozen storage on functionality of meat for processing

Evaluation of methylxanthines and related compounds to enhance clostridium perfringens sporulation using a modified duncan and strong medium

Antibotulinal properties of selected aromatic and aliphatic aldehydes

Combined water activity and solute effects on growth and survival of Listeria monocytogenes Scott A

Caffeic acid activity against Clostridium botulinum spores