Formulation and Evaluation of a Selective Medium for Lactic Acid Bacteria-Validation on Some Dairy Products
Baida Djeghri-Hocine, Messaouda Boukhemis and Abdeltif Amrane
DOI : 10.3844/ajabssp.2010.148.153
American Journal of Agricultural and Biological Sciences
Volume 5, 2010
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.
© 2010 Baida Djeghri-Hocine, Messaouda Boukhemis and Abdeltif Amrane. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.