Phenyllactic acid (PLA) is a naturally occurring organic acid present across various biological systems. It holds significance due to its diverse biological activities. It is found in plants, animals, and is particularly noted for its production by microorganisms.
Origins and Formation
In plants, PLA can be a precursor in the biosynthesis of more complex compounds. In animals, it is a metabolite that can accumulate in certain metabolic disorders.
A significant source of phenyllactic acid is its production by microorganisms, especially lactic acid bacteria (LAB). These bacteria, including genera like Lactobacillus, Pediococcus, and Weissella, are commonly found in fermented foods. The biosynthesis of PLA in LAB primarily occurs through the amino acid metabolism pathway.
This process involves the transamination of phenylalanine into phenylpyruvic acid (PPA). Phenylpyruvic acid is then reduced to phenyllactic acid by enzymes. While naturally produced in low amounts, supplementing growth media with phenylalanine or PPA can increase PLA yields.
Biological Roles and Mechanisms
Phenyllactic acid exhibits broad-spectrum antimicrobial properties, inhibiting the growth of various undesirable microbes, including bacteria and fungi. This makes it a natural preservative, even effective under low-temperature conditions. Its inhibitory effects have been demonstrated against several fungal species, including mycotoxigenic ones like Aspergillus ochraceus and Penicillium verrucosum, as well as bacterial contaminants such as Listeria spp. and Staphylococcus aureus.
The mechanisms by which PLA exerts its antimicrobial action are multifaceted. Similar to other weak acid preservatives, PLA can disrupt the cell membranes of microorganisms. This disruption can interfere with cellular integrity and transport processes, ultimately leading to cell damage.
PLA can also inhibit microbial growth by affecting enzyme activity and metabolic pathways within the target organisms. Studies have indicated that at sub-inhibitory concentrations, PLA can slow the radial growth of fungal colonies and inhibit their sporulation. The L-isoform of PLA is often a more potent inhibitor than its D-form. This inhibition of spore synthesis is particularly beneficial in food preservation, as many foodborne fungi are spread by airborne spores.
Beyond its antimicrobial effects, PLA also exhibits other biological activities. It has antioxidant properties, contributing to the overall stability of products. Research also suggests its role as a signaling molecule in certain biological contexts, although these areas require further investigation to fully understand their implications.
Presence in Food and Health Connections
Phenyllactic acid is commonly found in various fermented foods, where it contributes to both preservation and flavor. It is present in products like sourdough bread, yogurt, and cheese. In these foods, LAB strains produce PLA as a byproduct of their metabolic activity, acting as a biopreservative that helps extend shelf-life by inhibiting spoilage organisms and pathogens.
The presence of PLA in fermented foods also connects to human health through its interaction with gut microbiota. As a compound consumed through diet, it may influence the composition and activity of microorganisms within the digestive system. However, the precise mechanisms and long-term effects of this interaction are still subjects of ongoing research.
PLA’s involvement in human metabolic pathways is also being explored. While a naturally occurring metabolite, its accumulation has been observed in specific genetic conditions, such as phenylketonuria, where it can be considered a toxic product. Despite this, studies on cell lines have indicated that PLA is non-toxic. Research continues to investigate the broader implications of dietary PLA on human health and its potential roles in various physiological processes.