Design of biopolymeric matrices entrapping bioprotective lactic acid bacteria to control Listeria monocytogenes growth: Comparison of alginate and alginate-caseinate matrices entrapping Lactococcus lactis subsp lactis cells

In order to design biopolymeric matrices entrapping bioprotective lactic acid bacteria (LAB) to control undesirable microorganisms growth in foods, the performances of alginate and alginate-caseinate (an aqueous two-phase system) matrices entrapping Lactococcus lactis subsp. lactis LAB3 cells were compared. Since efficient matrices should preserve the culturability and the antimicrobial activity of entrapped LAB3 cells for prolonged periods, they were both monitored for 12 days storage at 30 degrees C. Maximal cell density (similar to 10(9) CFU mL(-1)) was reached after 24 h whatever the matrix type. Then, the LAB3 cells population decreased: 10(7) and 10(6) CFU mL(-1) were enumerated after 12 days in alginate-caseinate matrix and in alginate matrix, respectively. The anti-listerial activity assayed by an agar well method of LAB3 cells entrapped in alginate-caseinate matrices was also higher. LAB3 cells anti-listerial activity has been shown to be due to antimicrobial metabolites: hydrolysis by proteolytic enzymes of LAB3 cell-free culture supernatants (CFS) demonstrated the proteinaceous nature of at least a part of these metabolites. The higher antimicrobial activity of alginate-caseinate matrices might both result from the higher survival rate of bacterial cells and from a higher release of antimicrobial metabolites. To test this latter hypothesis, LAB3 CFS were incorporated in alginate and alginate-caseinate matrices and tested against Listeria innocua and Listeria monocytogenes. The anti-listerial activity of LAB3 CFS was higher in alginate-caseinate matrices indicating a better release of antimicrobial agents from this matrix. Alginate-caseinate matrices are thus better suited for LAB3 cells incorporation both for their survival and to promote the release of their antimicrobial metabolites. (C) 2013 Elsevier Ltd. All rights reserved.