L'impact de la viabilité des bactéries lactiques sur la qualité des laits fermentés du marché

Abstract

This study evaluates the microbiological and physicochemical quality of four fermented dairy products (Lben, Activia yogurt, flavored stirred yogurt, and fresh cheese) collected from the Wilaya of Mostaganem, Algeria. The main objective was to assess the evolution of lactic acid bacteria (LAB) viability and the compliance of physicochemical parameters from the time of commercialization until the end of the shelf life (expiry date). Microbiological counts performed on MRS and M17 media revealed excellent viability of the starter cultures, with bacterial populations maintained between 10⁷ and 10¹⁰ CFU/mL at the end of storage, confirming both the sanitary quality and the biological activity of the products. Physicochemical analyses, including pH, titratable acidity, total solids, fat content, and protein content, demonstrated remarkable stability, reflecting effective industrial control of manufacturing processes Catalase tests were negative for all isolates, confirming the absence of contamination by aerobic microorganisms. The study also highlighted a metabolic distinction among the products: while yogurts and fresh cheese maintained stable homofermentative activity, Lben exhibited a late heterofermentative shift at the end of its shelf life, characterized by gas production. Rather than indicating spoilage, this phenomenon reflects the natural microbial biodiversity inherent to Lben. In conclusion, the analyzed products complied with regulatory requirements and maintained their functional properties throughout their shelf life, emphasizing the critical importance of cold chain management in preserving this living microbial ecosystem.