Breaking down the microbiology world one bite at a time
Raw milk may hold the key to healthier food preservation
Food preservation has long been a challenge in the food industry. Historically, chemical preservatives such as sorbate, benzoate and nitrate have been used. However, consumers have expressed interest in less processed foods. While one alternative, thermal treatment, has been used, nutritional value is lost and the generation of carcinogenic products has led to the restriction of this application. Another alternative is through fermentation and the use of lactic acid bacteria commonly found in foods such as yogurt and cheese. These bacteria can inhibit spoilage-causing microorganisms through the production of lactic acid as well as another substance called bacteriocins.
What are Bacteriocins?
Bacteriocins are proteins produced by prokaryotes that can have antimicrobial activity against closely related species (narrow-range) or a broad range of species. Bacteriocins are a safer, more targeted alternative to chemical preservatives. Their ability to be transferred to other bacteria makes them easier to produce on a large scale.
Novel Bacteriocin
In this study, researchers describe a new bacteriocin, Raffinocyclicin, a circular bacteriocin produced by Lactococcus raffinolactis APC 3967. Raffinocyclicin is highly resistant to pH, temperature and proteolytic action making it a promising addition to the food preservation industry.
How do we know it will work?
To test the antimicrobial spectrum of Raffinocyclicin, the researchers used a spot-on-lawn assay (see image below). In this assay, the targeted bacteria are grown on a culture plate. On this plate, the producer strain is grown first, in this case L. raffinolactis APC 3967. After an overnight incubation, the cells are killed using chloroform. Chloroform is a chemical that can permeate the cell wall and membrane. In doing so, chloroform dissolves the proteins holding the membrane together, thereby effectively killing the cell. Thus, all that remains is the activity of the bacteriocin. Then, the plate is overlaid with the targeted strains and those are allowed to grow overnight. The goal is inhibition of growth of the targeted bacteria which is measured by the appearance of an inhibitory halo where the bacteriocin exists in the culture plate.
Spot on lawn assay showing the seed layer of L raffinolactis and the zone of inhibition. Image created by the author in biorender.
Does it work?
Strains of bacteria that were inhibited included common culprits of food spoilage such as Listeria monocytogenes and Clostridium perfringens. Unfortunately, no activity was seen against other common food pathogens such as Escherichia sp., Klebsiella pneumoniae, Pseudomonas aeruginosa and Bacillus cereus.
Natural Food Preservation
Raffinocyclicin can potentially play a role in providing a healthy alternative to preventing food spoilage as a biopreservative or even as a starter/safety culture in the fermentation process. In addition, the antimicrobial activity assay demonstrated an ability to inhibit common pathogens that infect humans as well, and thus it may have potential to be studied as a possible antibiotic as well. More studies would be needed to confirm its potential for either of these applications as this was the first study conducted on the species, but the future is bright for new approaches and techniques to preserve our food.
Link to the original post: Miceli de Farias F, O’Connor PM, Buttimer C, Kamilari E, Soria MC, Johnson CN, Deliephan A, Hill D, Fursenko O, Wiese J, Draper LA, Stanton C, Hill C, Ross RP.2024.Raffinocyclicin is a novel plasmid-encoded circular bacteriocin produced by Lactococcus raffinolactis with broad-spectrum activity against many gram-positive food pathogens. Appl Environ Microbiol 90:e00809-24. https://doi.org/10.1128/aem.00809-24
Featured image: created in Deep AI
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