6533b86dfe1ef96bd12cab4c

RESEARCH PRODUCT

Preservation of viability and anti-Listeria activity of lactic acid bacteria, Lactococcus lactis and Lactobacillus paracasei, entrapped in gelling matrices of alginate or alginate/caseinate

subject

description

In order to control undesirable microorganisms growth in foods, the performance of alginate and alginate-caseinate (an aqueous two-phase system) matrices entrapping lactic acid bacteria (LAB) (Lactobacillus paracasei LAB1 and Lactococcus lactis LAB3) was investigated. Polymeric matrices were initially loaded with Lcells at similar to 10(8-10) or similar to 10(4-6) CFU mL(-1), and were monitored, in liquid and gelled form (beads), for 12 days at 30 degrees C. In the liquid form, maximum cell density (similar to 10(9) CFU mL(-1)) was reached after 24 h whatever the matrix. Then, the Lpopulation decreased but remained higher in alginate-caseinate matrices: 10(7) and 10(6) CFU mL(-1) of LAB3 cells were enumerated after 12 days in alginate-caseinate and in alginate matrices, respectively. Anti-Listeria activity (assayed by agar well diffusion method) did not vary much over 12 days and was also higher for cells entrapped in alginate-caseinate matrices. When matrices were gelled, similar trends were observed: at "Day 12", LAB3 population was 10(4-5) and 10(2-3) CFU/bead, and, LAB1 population was 10(5-6) and 10(3-4) CFU/bead, in alginate-caseinate and alginate beads, respectively. Antimicrobial activity of alginate-caseinate beads containing LAB1 cells was quite constant over 12 days. The anti-Listeria activity of Lcell-free supernatants incorporated in matrices with caseinate was also higher. In fact, the presence of caseinate was shown to promote both the survival of Lcells and the release of their antimicrobial metabolites. Observation of liquid and gelled matrices by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) revealed a preferential localization of Lcells in casein-rich microdomains which could affect favorably the efficiency of bipolymeric matrices. (C) 2014 Elsevier Ltd. All rights reserved.