Microbial biotransformation of N-nitro-, C-nitro-, and C-nitrous-type mutagens by Lactobacillus delbrueckii subsp. bulgaricus in meat products

Mutagens in commercial food processing and its microbial transformation

Mutagens are chemical molecules that have the ability to damage DNA. Mutagens can enter into our body upon consumption of improperly cooked or processed food products such as high temperature or prolonged cooking duration. Mutagens are found in the food products can be classified into N-nitroso derivatives, polycyclic aromatic hydrocarbons, and heterocyclic aromatic amines. Food products with high fat and protein content are more prone to mutagenic formation. Microorganisms were found to be a potent weapon in the fight against various mutagens through biotransformation. Therefore, searching for the microorganisms which have the ability to transform mutagens and the development of techniques for the identification as well as detection of mutagens in food products is much needed. In the future, methods for the identification and detection of these mutagens as well as the identification of new and more potent microorganisms which can transform mutagens into non-mutagens are much needed.

A Review on the Role of Lactic Acid Bacteria in the Formation and Reduction of Volatile Nitrosamines in Fermented Sausages

Nitrosamines are N-nitroso compounds with carcinogenic, mutagenic and teratogenic properties. These compounds could be found at certain levels in fermented sausages. Fermented sausages are considered to be a suitable environment for nitrosamine formation due to acid formation and reactions such as proteolysis and lipolysis during ripening. However, lactic acid bacteria (spontaneous or starter culture), which constitute the dominant microbiota, contribute significantly to nitrosamine reduction by reducing the amount of residual nitrite through nitrite degradation, and pH decrease has an important effect on the residual nitrite amount as well. These bacteria also play an indirect role in nitrosamine reduction by suppressing the growth of bacteria that form precursors such as biogenic amines. In recent years, research interest has focused on the degradation or metabolization of nitrosamines by lactic acid bacteria. The mechanism by which these effects are seen has not been fully understood yet. In this study, the roles of lactic acid bacteria on nitrosamine formation and their indirect or direct effects on reduction of volatile nitrosamines are discussed.

Use of Starter Cultures in Foods from Animal Origin to Improve Their Safety

Starter cultures can be defined as preparations with a large number of cells that include a single type or a mixture of two or more microorganisms that are added to foods in order to take advantage of the compounds or products derived from their metabolism or enzymatic activity. In foods from animal origin, starter cultures are widely used in the dairy industry for cheese, yogurt and other fermented dairy products, in the meat industry, mainly for sausage manufacture, and in the fishery industry for fermented fish products. Usually, microorganisms selected as starter culture are isolated from the native microbiota of traditional products since they are well adapted to the environmental conditions of food processing and are responsible to confer specific appearance, texture, aroma and flavour characteristics. The main function of starter cultures used in food from animal origin, mainly represented by lactic acid bacteria, consists in the rapid production of lactic acid, which causes a reduction in pH, inhibiting the growth of pathogenic and spoilage microorganisms, increasing the shelf-life of fermented foods. Also, production of other metabolites (e.g., lactic acid, acetic acid, propionic acid, benzoic acid, hydrogen peroxide or bacteriocins) improves the safety of foods. Since starter cultures have become the predominant microbiota, it allows food processors to control the fermentation processes, excluding the undesirable flora and decreasing hygienic and manufacturing risks due to deficiencies of microbial origin. Also, stater cultures play an important role in the chemical safety of fermented foods by reduction of biogenic amine and polycyclic aromatic hydrocarbons contents. The present review discusses how starter cultures contribute to improve the microbiological and chemical safety in products of animal origin, namely meat, dairy and fishery products.

The potential of bacterial cultures to degrade the mutagen 2-methyl-1,4-dinitro-pyrrole in a processed meat model

Processed meats are classified by the International Agency for Research on Cancer as category 1 because their consumption increase the incidence of colorectal and stomach cancers. Meat processing widely employs nitrite and sorbate as preservatives. When these preservatives are concomitantly used in non-compliant processes, they may react and produce the mutagen 2-methyl-1,4-dinitro-pyrrole (DNMP). This study aimed to evaluate the ability of different bacteria isolated from food matrices to biodegrade DNMP in in vitro reactions and in a processed meat model. A possible mechanism of biodegradation was also tested. In vitro experiments were performed in two steps. In the first one, only one strain out of 13 different species did not interact with DNMP. In the following step, an empirical conversion factor was calculated to assess the conversion of DNMP to 4-amino-2-methyl-1-nitro-pyrrole by the strains. The most efficient strains were Staphylococcus xylosus LYOCARNI SXH-01, Lactobacillus fermentum LB-UFSC 0017, and Lactobacillus casei LB-UFSC 0019, which yielded conversion factors of 0.62, 0.60, and 0.43, respectively. Thus, such strains were individually added to the processed meat model and completely degraded the DNMP. Moreover, S. xylosus degraded DNMP in less than 30 min. The enzymatic mechanism was evaluated using its cell-free extract. It showed that, in the aerobic system, reduction rates were 30.321 and 22.411 nmol/mg of protein/min using NADH and NADPH, respectively. A DNMP reductase was assigned to the extract and a potential presence of an oxygen insensitive nitroreductase type I B was considered. Thus, biotechnological processes may be an efficient strategy to eliminate the DNMP from meat products and to increase food safety.