Chapter 20: Food Spoilage by Fungi and How to Prevent It

Fungal spoilage encompasses both visible degradation—changes in appearance, texture, odor, or flavor—and invisible contamination by mycotoxins that render food unsafe despite normal appearance. With approximately one-quarter of global harvested produce lost to fungal damage before reaching consumers, this represents a significant food security challenge affecting fruits, vegetables, grains, meats, and dairy products at multiple stages. The chapter identifies three primary mechanisms by which fungi compromise food: plant pathogens that continue deteriorating harvested tissue, necrotrophs that secrete toxins before saprophytic feeding, and specialized saprobes adapted to extreme food environments. These fungal groups possess remarkable tolerance mechanisms, including xerotolerance for survival in low-moisture conditions, psychrotolerance for growth at subfreezing temperatures, thermotolerance for heat resistance, acid tolerance for survival in acidic foods, and microaerophily for growth with minimal oxygen. Specific fungal species are linked to characteristic food spoilage patterns, such as Rhizopus stolonifer causing bread mold, Botrytis cinerea devastating berries, Penicillium species rotting citrus and apples, and Monilinia browning stone fruits. Certain fungi including Aspergillus and Fusarium produce dangerous secondary metabolites like aflatoxins, ochratoxins, vomitoxin, and zearalenone that contaminate grains and nuts. Prevention strategies operate along two principles: eliminating fungal propagules through sterilization, irradiation, or filtration, or inhibiting growth through environmental manipulation. Water activity reduction via drying, refrigeration for slowing metabolism, freezing for dormancy induction, chemical preservatives like propionates and benzoates, and oxygen exclusion through canning or modified atmosphere packaging all demonstrate the multi-faceted approach required. The chapter emphasizes that because fungal spores are ubiquitous in nature, absolute prevention is impossible; rather, effective food preservation combines multiple complementary techniques tailored to specific food categories and storage conditions.