Antilisterial Efficacy of Pediococcus acidilactici AA5a as Proniotic Inoculum in Carrot Juice Substrate

Abstract

This study aimed to establish the antilisterial efficacy of Pediococcus acidilactici AA5a as probiotic inoculum in carro: juice substrate. P. acidilactici AASa produces bacteriocins that inhibit certain bacterial strains such as Listeria monocytogenes, a food pathogen that is known to contaminate a variety of foodstuffs including vegetables. Results from this study would show preliminary data on the effectivity of P. acidilactici AAb5a as an antilisterial agent in a probiotic carrot juice drink. The first stage of the study involved observation of the growth and bacteriocin activity of P. acidilactici AA5a in the substrate and the corresponding pH and residual reducing sugar content of the substrate over a 24-h fermentation period at 4-h intervals. In the second stage, the antilisterial efficacy of P. acidilactici AAS5a was evaluated by determining what inoculum concentration of P. acidilactici AASa (5-8 log CFU/ml) would inhibit a population of 5 log CFU/ml Listeria grayi CM904 in the substrate over a 24-h period at 6-h intervals. Using plate counting and ‘spot-on-lawn’ assay, it was observed that the highest inoculum concentration, 8 log CFU/ml resulted to a consistent and greater decrease in the population count of L. grayi. It was also noted that bacteriocin activity increased with bacterial growth. The pH and reducing sugar content also decreased due to the fermentative activity of this bacteriocinogenic strain. Antilisterial efficacy of P. acidilactici AA5a increased with inoculum concentration. The most effective concentration was 8 log CFU/ml but it was still not enough to completely inhibit L. grayi CM904 due to adhesion of bacteriocins to the pulp. New formulations of the substrate and longer observation periods may be done for further testing.