Characterization and Antilisterial Potential of Lactic Acid Bacteria and Yeasts Isolated from Fermenting Cow Milk

Abstract

Scientists and the food business are currently interested in a vast range of microbes called lactic acid bacteria (LAB) and yeasts. Despite playing a significant role in the taste improvement of fermented foods, their antimicrobial qualities haverecently come to light. Standard techniques were used in this investigation to describe the LAB and yeasts derived fromthe fermented milk primarily on their morphological, microscopic, and biochemical characteristics. Furthermore,antilisterial activities of lactic acid bacteria and yeasts were performed. Also, the antilisterial activities of neutralized LABand yeasts and the effect of treatment of pH, NaCl, and enzyme activities against Listeria monocytogenes were performed. Lastly, a co-culture of LAB and yeast with Listeria monocytogenes in skimmed milk was done. Twenty lactic acid bacteriaisolates obtained from fermented cow milk were characterised as Lactobacillus rhamnosus, Lactobacillus plantarum,Lactobacillus delbrueckii, Lactobacillus brevis, Lactobacillus casei, Lactobacillus fermentum, and Lactococcus lactis while twenty- five yeast isolates obtained from fermented cow milk were identified as Saccharomyces cerevisiae,Debaryomyces hansenii, Pichia anomala, Kluyveromyces lactis, Trichosporon mucoides, Saccharomyces barnettii and Saccharomyces bayanus with different frequency. The secretion of metabolites like organic acids, hydrogen peroxide,diacetyl, and bacteriocin by lactic acid bacteria led to the inhibition of Listeria monocytogenes, whereas the synthesis oforganic and volatile acids, substantial quantities of ethanol, hydrogen peroxide, while mycocins by yeasts led to theirinhibition. When treated with -amylase and at pH 4–7, bacteriocins and mycocins remained constant, but part of their activity was reduced when treated with protease. As pH and NaCl concentration increased, the activity of bacteriocins and mycocins decreased. In the presence of the LAB and yeasts, Listeria monocytogenes showed a delay in growth and lowmicrobial count for the control during the co-culturing experiment.
Keywords: Listeria monocytogenes, Lactic acid bacteria, Yeasts, cow milk, antilisterial activities.