The preservative effect of lactic acid bacteria during the manufacture and subsequent storage of fermented foods is mainly due to the acidic conditions that they create in the food during their development. This souring effect is primarily due to the fermentative conversion of carbohydrates to organic acids (lactic and acetic acid) with a concomitant lowering of the pH of the food, an important characteristic that leads to an increased shelf-life and safety of the final product. In recent decades, it has become clear that the overall inhibitory action of lactic acid bacteria is due to more complex antagonistic systems produced by the starter cultures. Lactic acid bacteria are capable of producing and excreting inhibitory substances other than lactic and acetic acid. These substances are antagonistic to a wide spectrum of microorganisms, and thus can make significant contributions to their preservative action. They are produced in much smaller amounts than lactic acid and acetic acid, and include formic acid, free fatty acids, ammonia, ethanol, hydrogen peroxide, diacetyl, acetoin, 2,3-butanediol, acetaldehyde, benzoate, bacteriolytic enzymes, bacteriocins and antibiotics, as well as several less well-defined or completely unidentified inhibitory substances (Klaenhammer, 1988; Daeschel, 1989; Lind-gren & Dobrogosz, 1990; Schillinger, 1990; Piard & Desmazeaud, 1991, 1992; Vandenbergh, 1993). Some of these substances display antagonistic activity towards many food spoilage and foodborne pathogenic microorganisms, including psychrotrophic lactobacilli and leuconostocs, Bacillus cereus, Clostridium botulinum, Clostridium perfringens, Listeria monocytogenes, Staphyloc-occus aureus, etc. The competitive removal of essential substrates, the accumulation of D-amino acids, a lowering of oxidation-reduction potential and coaggregation may further restrict undesirable microorganisms. Unfortunately, in some instances the antibiosis will be detrimental by inhibition of other desirable lactic strains composing the mixed starter culture.

Antimicrobial Potential of Lactic Acid Bacteria

Growth factors and antimicrobial factors of bovine colostrum

Lysozyme (LZ), lactoferrin (LF), lactoperoxidase (LP), immunoglobulin G and secretory immunoglobulin A were extracted from camel milk. The activity of these protective proteins was assayed against Lactococcus lactis subsp. cremoris, Escherichia coli, Staphylococcus aureus, Salmonella typhimurium and rotavirus. Comparative activities of egg white LZ, bovine LZ and bovine LF are also presented. The antibacterial activity spectrum of camel milk LZ was similar to that of egg white LZ, and differed from bovine milk LZ. Bovine and camel milk LF antibacterial activity spectra were similar. The camel milk LP was bacteriostatic against the Gram-positive strains and was bactericidal against Gram-negative cultures. The immunoglobulins had little effect against the bacteria but high titres of antibodies against rotavirus were found in camel milk. The LP system was ineffective against rotavirus.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022029900030417

Antibacterial and antiviral activity of camel milk protective proteins

The natural antimicrobial system present in milk, the lactoperoxidase (LP) system, has been used to preserve raw milk quality in areas where it is not possible to use mechanical refrigeration for technical and/or economic reasons. Although the most widely recommended industrial application of the LP system in food production is in the dairy industry for the preservation of raw milk during storage and/or transportation to processing plants, other novel applications of the LP system are being explored. This review paper addresses the use of the LP system in the dairy industry, new research findings and developments made so far and the potential applications of the LP system in other food systems and commercial products. The paper also highlights the research gap and possible future research directions that deserve attention.

Significance of the lactoperoxidase system in the dairy industry and its potential applications: a review

Lactic acid bacteria present in the human and animal gut are introduced through fermented milk products, food and feed supplements containing viable bacteria. Lactobacillus species, such as L. acidophilus, L. bulgaricus, L. lactis along with B. bifidum and Streptococcus faecium constitute an integral part of the healthy gastro-intestinal microecology and are involved in the host metabolism. They impart nutritional and therapeutic benefits to the consumer. The vitamins and enzymes produced by the lactic acid bacteria contribute to host metabolism. The antimicrobial substances produced by these bacteria control the proliferation of undesired pathogens. They also elaborate enzymes that aid host metabolism. This is particularly true in case of lactase nonpersistent individuals. Their anticholesteremic properties assist in lowering serum cholesterol. It has been suggested that the tumor suppression trait of these microbes reduces the incidence of colon cancer.

Therapeutic role of dietary lactobacilli and lactobacillic fermented dairy products

Two strains of Escherichia coli and one strain each of Salmonella typhimurium and Pseudomonas aeruginosa were killed by the bactericidal activity of the lactoperoxidase-thiocyanate-hydrogen peroxide system in milk and in a synthetic medium. H2O2 was supplied exogenously by glucose oxidase, and glucose was produced at a level which was itself noninhibitory. Two phases were distinguished: the first phase was dependent on the oxidation of SCN(-) by lactoperoxidase and H2O2, which was reversed by reducing agent, and the second phase was dependent on the presence of accumulated H2O2, which was reversed by catalase. The latter enzyme could also reverse the first phase, but only when present in excessive and unphysiological levels. The bactericidal activity was greatest at pH 5 and below, and it depended on the SCN(-)concentration and on the number of organisms. Since raw or heated milk neutralizes the acid barrier against infection in the stomach, the bactericidal system discussed may contribute to the prevention of enteric infections in neonates.

https://iai.asm.org/content/iai/13/3/800.full.pdf

Nonspecific bactericidal activity of the lactoperoxidases-thiocyanate-hydrogen peroxide system of milk against Escherichia coli and some gram-negative pathogens.

B Reiter

Papers

Nonspecific bactericidal activity of the lactoperoxidases-thiocyanate-hydrogen peroxide system of milk against Escherichia coli and some gram-negative pathogens.