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It is obvious that for meat preservation, synthetic chemicals have been traditionally used to inhibit resident pathogenic and spoilage microorganisms in refrigerated products. This is cause of increasing consumer concerns of potential health risks associated with some of synthetic preservatives has led researchers to evaluate the opportunity of using natural bio-preservatives such as Lactic Acid Bacteria (LAB) selected for their inhibitory activity towards undesirable microorganism.
In the recent work, Alireza Goodarzi shows that by the use of rifampicin (rif) resistance mutant of Lactobacillus acidophilus can be improved bio-preservation shelf life of meat during storage in refrigerator. Lactic acid bacteria widely used in food preservation at refrigerator temperatures due to their ability produce high amount of hydrogen peroxide and/or other antibacterial substances at refrigerator temperatures to inhibit food-borne pathogens and psychrophilic spoilage microorganisms. Most raw foods are contaminated with pathogenic and spoilage microorganisms. Ground beef products are common sources of E. coli O157:H7 and its reduction is an important concern in the beef industry. It was shown LAB impact on E. coli O157:H7 viability in ground beef and the sensory properties of these products.
The objective of this work was selection rif resistance mutants of L. acidophilus possessing high hydrogen peroxide production ability and evaluation their impact on E. coli O157:H7 in ground beef during refrigerated storage.
“Among UV-mutagenized population of L. acidophilus Rif mutants producing high amounts of H2O2 were selected. Rif mutants produced significant amounts of hydrogen peroxide 50-55 μg/ml in sodium phosphate buffer (0.2 M, pH 6.5) and in beef broth (BB) at 5 °C for 5 days submerged cultivation without of growth”, Alireza Goodarzi.
The mutants possess higher impact against food-borne pathogen Escherichia coli O157: H7 at refrigeration temperatures and for 3 days reduces the pathogen total amount practically undetectable level. Rif mutants L. acidophilus reduced initial amount 2×105 of E. coli O157: H7 in ground beef up to 3 log for 3 days of solid-state cocultivation when the wild strain reduced only 2 log. The application of L. acidophilus mutants did not cause any changes in sensory characteristics of ground beef, moreover promotes expanding of shelf-life due to inhibition of psychrophilic spoilage microorganisms.
Resistant to rifampicin mutants of mutants L. acidophilus exert higher inhibitory action against E. coli O157:H7 and practically fully eliminate the pathogen bacteria from ground beef at refrigeration temperatures. Rif mutations can be successfully used as a tools in biotechnology for improving preservative properties of LABs intended for commercial applications.
Author: Alireza Goodarzi
"Armbiotechnology" Scientific and Production Center NAS RA, Yerevan, Armenia.