The Growth Conditions, Enzyme Action, Mould Growth and Yeast Production

Growth Conditions for Food Spoilage Organisms

Understand the four basic growth conditions required for bacteria, yeast and mould: food, acidity, time, temperature and oxygen.

Microorganisms grow best on high-protein foods like meats, poultry, seafood, dairy products and cooked starches.

Spoilage organisms grow best in the natural acidity (pH) found in foods. Moulds and yeasts can grow in more acidic conditions.

Most bacteria, yeast and moulds grow rapidly in the “Danger Zone” temperatures between 8°C and 60°C.

Spoilage can occur quickly if food is left out at room temperature beyond two hours.

Aerobic bacteria require oxygen to grow, while anaerobic bacteria can grow without it. Some bacteria, like yeasts, can grow with or without oxygen.

Enzymes are protein molecules that catalyse or speed up chemical reactions in foods and cause changes such as browning, flavour changes, and nutrient loss.
Browning enzymes like polyphenol oxidase can cause food to darken when exposed to air. This can be controlled by applying heat, acid or reducing agents.
Lipase enzymes break down fats and oils, producing rancidity. Keep food cool or freeze it to slow down these enzymes and prolong the food’s shelf life.

Moulds are fungal organisms that can live in a wide range of habitats and grow on many different substrates, including food.
Certain moulds produce mycotoxins, harmful compounds that can cause illness. Never eat visibly mouldy food.
To prevent mould growth, store food properly. For example, bread should be kept in a cool, dry place, and fruits and vegetables should be refrigerated.

Yeasts are single-celled fungi that reproduce by budding and can cause fermentation in foods, often causing them to spoil.
Some yeasts are used deliberately in food production, such as in baking bread and brewing beer.
Yeast in beverages can produce carbon dioxide gas, which can cause the containers to bulge or burst.
Yeast can be controlled by keeping food cool and dry and by controlling the acidity of the food.