Detoxification of aflatoxin M1 by eight lactic acid bacteria strains, alone or in combination, as viable and heat-killed cells in PBS, MRS broth, and Karish cheese

Abstract

Abstract Aflatoxin M1 (AFM1) in milk is a major public health concern. It is a hydroxylated metabolite of aflatoxin B1 (AFB1), formed in the liver of animals after ingestion of contaminated feed and subsequently excreted into milk. Biological techniques could be used to combat this hepatotoxic and carcinogenic toxin. Therefore, this study evaluated the ability of eight lactic acid bacteria (LAB) strains to reduce AFM1 levels in phosphate-buffered saline (PBS), MRS broth, and Karish cheese using viable cells, while heat-inactivated cells, rendered non-viable by thermal treatment, were evaluated only in PBS. Eight standard LAB strains were tested, including Lactobacillus acidophilus (L. acidophilus) ATCC 4356 , Lactobacillus johnsonii (L. johnsonii) ATCC 3320 , Lactobacillus salivarius (L. salivarius) TISTR 390 , Lactobacillus bulgaricus (L. bulgaricus) EMCC-3 , Lactobacillus paracasei (L. paracasei) TISTR 453 , Lactobacillus helveticus (L. helveticus ) LH-BO2 , Streptococcus thermophilus (S. thermophilus) EMCC-2, and Bifidobacterium animalis subsp. lactis (B. animalis subsp. lactis) Bb12. Viable cells exhibited strong detoxification efficiency, with L. acidophilus ATCC 4356 achieving the highest AFM1 reduction (≈76%), followed by B. animalis subsp. lactis Bb12 and L. salivarius TISTR 390. Heat-killed counterparts showed minimal activity, confirming the essential role of metabolic processes in toxin removal. In MRS broth, a significant relationship was observed between pH decline and AFM1 degradation, where up to 80% reduction occurred at pH 3.0 after 20 days, emphasizing the influence of acidic and enzymatic conditions. Application in Karish cheese demonstrated the practical relevance of LAB under real food conditions. Mixed cultures of S. thermophilus EMCC-2, L. bulgaricus EMCC-3, and L. acidophilus ATCC 4356 or L. salivarius TISTR 390 reduced AFM1 by 74–78% after 20 days at 4 °C, accompanied by gradual acidification during ripening. In conclusion, these findings demonstrate that lactic acid bacteria (LAB), particularly multi-strain systems, effectively reduce aflatoxin M₁ (AFM₁) levels in dairy matrices.