Psychrotrophs

Psychrotrophs are microorganisms that can grow at refrigeration temperatures, typically around 0 to 7°C, but have optimum growth temperatures above 15°C. They are adapted to cold environments and are distinguished from true psychrophiles by their higher temperature of maximum growth. Psychrotrophs are common in soil, water, and particularly in food-processing environments, where they can contaminate products kept in the cold chain.

Physiologically, psychrotrophs maintain metabolic activity at low temperatures through adaptations such as membrane fatty acid composition that preserves fluidity, cold-active enzymes, and cold-shock responses. Their growth is slower at low temperatures, but they can multiply rapidly when temperatures rise toward their optimum, enabling them to cause spoilage during refrigerated storage.

Bacteria dominate the group and include genera such as Pseudomonas, Listeria monocytogenes, Brochothrix thermosphacta, and some Bacillus species, as well as various yeasts and molds. Listeria monocytogenes is of particular concern in food safety because it can grow at refrigeration temperatures and in some foods with low acidity, posing a risk to vulnerable populations.

In food microbiology, psychrotrophs are primarily implicated in spoilage of refrigerated products, including dairy, meat, fish, and ready-to-eat foods. They produce extracellular enzymes and metabolites that degrade texture, flavor, and appearance, leading to quality loss even when products are kept cold.

Control of psychrotrophs relies on a robust cold chain, proper sanitation, and processing steps such as pasteurization or sterilization where appropriate, along with packaging and storage practices that limit post-process contamination and growth during storage.