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.
