Purpose: The objective of this study was to evaluate the synergistic effect of the lactic acid bacteria (LAB) strains, NP7 (Lactobacillus lactis) and FS56 (Lactococcus lactis), on the growth and survival of L. monocytogenes (strains: Brie, Scott A, Murray B and Auburn 311) on sprouted alfalfa seeds.
Methods: Four LAB treatments [(1) NP7 seed soak and NP7 sprout spray, (2) FS56 seed soak and FS56 sprout spray, (3) FS56 seed soak and NP7 sprout spray, (4) NP7/FS56 seed soak and NP7/FS56 sprout spray] were applied at 8.00 log CFU/ml to alfalfa sprouts containing pathogen concentration of approximately less than 1.00 log CFU/g. Two identical Sprouting apparatus were run simultaneously so that each trial with co-culture inoculated seeds (L. monocytogenes and LAB) could be accompanied with a matched control (L. monocytogenes only) over the course of five days. L. monocytogenes and LAB were enumerated everyday on Modified Oxford agar (MOX) and De man, Ragosa, Sharpe agar (MRS), respectively.
Results: In comparison with the control sample, sprouts treated with only a single LAB strain (Treatments 1 and 2) had significant reduction of L. monocytogenes (P < 0.05) on days 1 and day 2 of sprouting. In the sprouts treated with a co-culture LAB (treatments 3 and 4), there was significant reduction (P < 0.05) on all days. The most significant reductions were observed for treatment 4, (4.41 log CFU/g) reduction and no detection of pathogen cells by direct plating at day 5.
Significance: The co-culture LAB treatments displayed stronger inhibition activity than the single LAB strain treatments, and this method might prove to be an efficacious natural method to control pathogen outgrowth during the sprouting stages of alfalfa sprouts.