Chapter 41: Food Microbiology – Spoilage, Fermentation & Safety

Chapter 41 details the dual roles of microorganisms in food, encompassing their capacity to cause spoilage and illness, as well as their essential use in producing fermented delights. Microbial growth in food is controlled by intrinsic factors, such as the food's chemical composition (e.g., carbohydrates favoring fungal spoilage; proteins and fats supporting bacterial putrefaction) and its water availability, pH, and physical structure. Extrinsic factors, including temperature, relative humidity, and the storage atmosphere, are also critical for preservation. Methods for controlling spoilage organisms involve physical processes like filtration, temperature modulation (refrigeration, pasteurization, canning), and high hydrostatic pressure (pascalization). Chemical controls use regulated substances (GRAS list) like organic acids or sodium nitrite to inhibit pathogens such as Clostridium botulinum, while radiation (radappertization) utilizes gamma rays to generate reactive oxygen species. Furthermore, packaging technologies like Modified Atmosphere Packaging (MAP) manipulate CO2 and O2 levels to extend shelf life. Food-borne illnesses are differentiated into infections, which require the pathogen to grow in the host (e.g., Listeria monocytogenes or E. coli O157:H7), and intoxications, which result from consuming toxins pre-formed in the food (e.g., Staphylococcus aureus or fungal aflatoxins and fumonisins). To prevent outbreaks, rapid and specific detection methods are employed, transitioning from traditional culture-based assays to modern molecular techniques, including nucleic acid methods (PCR, WGS), immunoassays, and biosensors. The PulseNet system, which uses PFGE to track outbreaks, is increasingly being replaced by Whole-Genome Sequencing (WGS) due to its superior resolution for pathogen subtyping. Finally, the chapter outlines fermentation, a critical process for developing foods like cheese, yogurt (using mesophilic or thermophilic lactic acid bacteria, or LAB), wine, and beer. Wine production involves yeast fermentation of grape must and malolactic fermentation by bacteria to reduce acidity. Beer requires initial malting and mashing of grains to create a fermentable wort before yeast inoculation. The production of complex foods like chocolate relies on a microbial succession of yeasts, lactic acid bacteria, and acetic acid bacteria to develop desirable flavors.