Lactic acid bacteria (LAB) isolated from fermented cocoa beans prevent the growth of model food-contaminating bacteria

Abstract

The application of lactic acid bacteria (LAB) for fermentation increases the quality of food particularly of cocoa product ensuring its palatability, shelf-life, and safety for consumption. This research aimed to identify the LAB isolated from fermented cocoa beans and conduct assays on their antibacterial activity against bacterial model strains of food-borne contaminants. The isolates were rejuvenated on De Man-Rogosa-Sharpe (MRS) media supplemented with 0.5 % calcium carbonate and grown in 30 °C for 48 h. The supernatants from cell homogenates were collected and tested against Escherichia coli, Bacillus subtilis, and Staphylococcus aureus. Four isolates of LAB namely: IDI-L009, IDI-L017, IDI-L039, and IDI-L049 demonstrated inhibitions against all three tested bacterial strains. The ability of supernatant of strain IDI-L009 to inhibit bacterial growth was abolished after neutralization by 1 N NaOH to pH 6.8 to 7. However, the supernatants of IDI-L017, IDI-L039, and IDI-L049 showed sound inhibition effect even after neutralization. It indicated that the three later LAB strains could produce secondary metabolite beyond common organic acids. The identification of LAB strains revealed that the identity of IDI-L009 was closest to a Pediococcus acidilactici, while IDI-L049 was highly similar to a Lactobacillus plantarum subsp. plantarum. Furthermore, the identities of IDI-L017 and IDI-L039 were closest to Lactobacillus pentosus.