Formulation and Evaluation of a Selective Medium for Lactic Acid Bacteria-Validation on Some Dairy Products

Abstract

Problem statement: Lactic Acid Bacteria (LAB) is characterized by fastidious nutritional requirements leading to the need for complex and rich media to allow growth. Owing to their complex requirements which also varied significantly with species, the formulation of selective media for LAB is difficult. Approach: A culture medium for LAB was previously developed based on deproteinated whey supplemented with yeast autolysate and de-lipidated egg yolk. Based on this previously developed medium, some selective media were formulated and their potential for LAB selection and enumeration was examined. Results: In this study, it was considered as a basis to define a selective medium, by adding a pH indicator and some inhibitory compounds to select the LAB flora of various dairy products including milk, disinfected or not, fermented milk and yoghurt. The addition of sodium azide to inhibit the contamination flora, including Gram negative floraand purple bromocresol allowed a direct selection of the Gram + and lactose + flora. An acidic pH (5.0) can also be helpfully considered after protein hydrolysis to avoid protein denaturation. Conclusion: To complete this study, additional work is needed concerning the improvement of culture medium selectivity by considering other inhibitors, of the Gram negative flora (like lithium chloride for instance), of fungi (like actidione), of the Gram positive flora (excepting the LAB flora) and an association of these inhibitors.

Optimization of Split Pea and Dry Figs-Based Media for the Growth of Lactobacillus plantarum through Plackett-Burman and Response Surface Methodological Approaches

“…Their growth is possible only on rich and complex culture media which must essentially comprise a source of nitrogen (amino acid, peptide), a carbon source, vitamins, minerals and trace elements. These nutrients must be made to optimal concentrations (Djeghri-Hocine et al, 2010). Therefore, determining a suitable growth media appears to be difficult.…”

Formulation of Culture Medium for the Enumeration of Lactic Streptococci and Lactobacilli from Fermented Milk Products

“…"Sodium azide was added to inhibit the contamination flora, including Gram negative flora and purple bromocresol allowed a direct selection of the Gram + and lactose + flora. For all samples medium M3 appeared to be the most appropriate for growth of Gram + and catalasebacilli, owing to the high growth rates and the colony diameters ranging from 1-2 mm" [18]. "LC (Lactobacillus casei) agar appeared appropriate for Lactobacillus paracasei and MRSB (MRS with bile) for yoghurt starter bacteria Latobacillus delbrueckii ssp.…”

Cultivation media for lactic acid bacteria used in dairy products

“…With regard to bulk media, additional steps are required for preparation and handling, and trained individuals must be involved in the preparation of the starter culture. There are also issues related to these media such as achieving high cell density and additional quality control steps to ensure that LAB reach maximum growth (Ibrahim and Daguri, 1995, 1996; Yamani and Ibrahim, 1996; Burns et al ., 2008; Djeghri-Hocine et al ., 2010; Hayek and Ibrahim, 2013). The literature reveals significant research aimed at developing new media or finding alternative low cost ingredients to lower costs or to obtain higher cell density (Kurbanoglu, 2004; Vázquez et al ., 2004 a , 2004 b ; Djeghri- Hocine et al ., 2007 a ; Aguirre et al ., 2008; Burns et al ., 2008; Zhang et al ., 2009; Djeghri-Hocine et al ., 2010).…”