Simulating the activity of the natural antimicrobial system of milk on the growth of selected cultures involved in cheesemaking and ripening

Abstract

The impact of three antimicrobial proteins (lactoferrin, lactoperoxidase, lysozyme) on the growth of cultures involved in cheesemaking and ripening was studied. Strains were grown in the optimal media growth of each strain or in cheese simulated environment. The media were supplemented with the antimicrobial proteins together (MIX; 1:1:1) or individually at concentrations found in milk (1x) and cheese (2.5x). Growth properties were evaluated using a novel approach by combining flow cytometry and spectrophotometric assay. Flow cytometry measures cell viability (live/injured/dead cells; total cells). Lactococcus cremoris CUC-C (starter culture) was stimulated by lactoperoxidase and lysozyme reaching higher optical density and total cells than control (without antimicrobial proteins). In cheese simulated environment, the live cells of L. cremoris CUC-C increased of more than 30% in the MIX condition without an increase in total cells. Flow cytometry allowed to show this protective effect. For cultures involved in ripening, the total cells of Lactiplantibacillus plantarum ATCC 14917 and Lacticaseibacillus paracasei subsp. tolerans LMA-1802 decreased of 1 log in the MIX condition. Although the same log reduction, different inhibition behavior was observed. Live cells for Lpb. plantarum ATCC 14917 remained unchanged while for Lcb. paracasei LMA-1802, injured cells increased. These observations were only possible by flow cytometry. The higher concentration (2.5x) tended to decrease the growth properties (lower maximal rate, longer lag phase) of strains as compared to the lower one (1x). The strain-dependent sensitivity to the three antimicrobial proteins underlines the importance of evaluating their effect on cultures prior cheesemaking to ensure proper functionality.