Abstract
Bioprotective Lactococcus lactis LAB3 cells that produce bacteriocin-like substances were entrapped in 4% (w/w) sodium alginate matrices, either with or without 10% (w/w) sodium caseinate. The effects of bead formulation-alginate alone or combined with caseinate, with or without the addition of 20% (w/w) MRS broth or M17 broth-on the culturability of Lc. Lactis LAB3 cells within the beads and their anti-Listeria activity were assessed over 12 days of storage at 30 °C in closed bottles. Calcium-alginate-caseinate beads supplemented with MRS broth proved most effective in preserving both culturability and anti-Listeria activity. Inoculum size (~10(6) or ~10(8) CFU mL(-1) initially) also played a role: only the higher initial inoculum yielded significant anti-Listeria activity after 12 days at 30 °C, despite a gradual decline over time, likely due to rapid nutrient depletion. In order to evaluate the feasibility of combining modified-atmosphere packaging with the addition of the Lc. lactis LAB3 bioprotective strain for preserving perishable foods, a prerequisite was to evaluate whether anti-Listeria activity persisted after 4 days of storage at 30 °C in calcium-alginate-caseinate beads containing either MRS or M17 broth under three different atmospheres. Beads entrapping Lc. lactis LAB3 cells stored in 20% (v/v) O(2)-80% (v/v) N(2) or in 60% (v/v) O(2)-40% (v/v) N(2) retained their anti-Listeria activity, whereas storage in 20% (v/v) CO(2)-80% (v/v) N(2) impaired this activity.