Changes in Acid-pH Resistance of Food Spoilage and Pathogens Spore-Forming Bacteria in Cameroonian Indigenous Sorghum-Based Acidic Beers before and after Sublethal Thermal Stresses
James Ronald Bayoï *
Department of Biological Sciences, Faculty of Science, University of Maroua, P.O.Box 814 Maroua, Cameroon.
Roger Djoulde Darman
Department of Agriculture, Livestock and Postharvest Technology, National Advanced School of Engineering, University of Maroua, P.O.Box 46 Maroua, Cameroon.
Francois-Xavier Etoa
Department of Microbiology, Faculty of Science, University of Yaounde I, P.O.Box 812 Yaounde, Cameroon.
*Author to whom correspondence should be addressed.
Abstract
Fermented alcoholic beverages play a major role in the socio-cultural lives of people of Northern Cameroon. However, reports of shelf-life and health problems associated with indigenous sorghum-based alcoholic beverages are a major call for concern. This study aimed to highlight the additional effects of sublethal temperatures (no thermal treatment and 10, 45, 50 and 60°C for 45, 90, 180 min) and acidic pH of beers (2.79 and 2.63 for 45, 90, 180 min) on fate of four food spoilage and pathogens spore-forming bacteria. The experiments were carried out on real food products formed by two indigenous sorghum-based alcoholic beverages. Pasteurized traditional beers were significantly efficient on all unstressed bacterial spores after 180 minutes of treatment. In addition, spores of B. megapterium and G. stearothermophilus were more sensitive in white beer pH 2.79 and red beer pH 2.63 respectively. Previous thermal treatments of spores at certain sublethal temperatures have significantly (P=0.05) decreased the effect of both acidic beers on stressed spores. It was noticed that the spores of B. subtilis stressed at 10°C, G. stearothermophilus (former Bacillus stearothermophilus) spores submitted at 45°C and the spores of B. cereus thermally stressed at 50°C and 60°C for 45, 90, 180 minutes were significantly (P=0.05) less affected by the white beer at pH 2.79. Whereas, in the red beer at pH 2.63, the spores of B. subtilis sublethally stressed at 10°C and the spores of B. cereus stressed at 45°C, 50°C and 60°C were more acid resistant and very weakly affected by acid pH of the alcoholic beverages. The study delivered some overview on the potential microbial (stability and safety) consequences of the current tendency towards milder cold and heat treatments which are greatly used in the food-grade industry.
Keywords: Bacillus spores, alcoholic sorghum-based beverages, acid pH, sublethal thermal stresses, food safety.