Bacteria, Yeasts, and Moulds

This section explains bacteria, yeasts, and moulds. Microorganisms are tiny living organisms that are not visible to the naked eye. They include bacteria, yeasts, and moulds. These microorganisms play important roles in food safety, food spoilage, and food production.

Bacteria:

• Bacteria are single-celled organisms that can multiply rapidly under the right conditions. Some bacteria are beneficial (e.g., those used in the production of cheese and yoghurt), but others can cause foodborne illnesses, such as Salmonella, E. coli, and Listeria.
• Conditions for bacterial growth: Bacteria thrive in warm, moist environments with a supply of food. They multiply rapidly in the temperature range of 5°C to 63°C, known as the danger zone.
• Control: To prevent bacterial growth, foods should be stored at correct temperatures (below 5°C for refrigeration, or above 63°C for hot foods), and good hygiene practices should be followed.

Yeasts:

• Yeasts are fungi that can cause food spoilage by fermenting sugars in food. Yeasts are responsible for the fermentation process in products such as bread, beer, and wine. However, they can also cause spoilage in foods like fruit juices and jams.
• Conditions for yeast growth: Yeasts need moisture, warmth (20°C-30°C), and a food source (usually sugars) to grow and reproduce.
• Control: Yeast growth can be controlled by refrigerating foods, using preservatives, or by sterilisation techniques such as pasteurisation.

Moulds:

• Moulds are also fungi and are visible to the naked eye. They grow as a fuzzy, green or black coating on food, such as bread, cheese, and fruits. Some moulds produce mycotoxins, which are toxic and can cause foodborne illness.
• Conditions for mould growth: Moulds grow best in humid, warm environments and on food that has a high moisture content.
• Control: Moulds can be controlled by storing food in dry, cool environments and by regularly checking for spoilage. Certain moulds can be killed by cooking or freezing, but some toxins may remain.

High-Risk Foods

High-risk foods are those that are most likely to support the growth of harmful microorganisms such as bacteria, yeasts, and moulds. These foods are particularly vulnerable to spoilage and contamination. They include:

• Cooked meats (e.g., roast chicken, ham, sausages)
• Dairy products (e.g., milk, cream, cheese)
• Eggs and dishes containing eggs (e.g., mayonnaise, quiche)
• Cooked rice and pasta
• Seafood (e.g., fish, shellfish)
• Prepared fruits and vegetables (e.g., salads, fruit juices)
• Foods containing sugar, such as jams and syrups

These foods need to be handled and stored carefully to prevent microbial contamination and spoilage.

Enzymes: Biological Catalysts

Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are usually made of protein and are vital for processes like digestion, metabolism, and fermentation. In food safety, enzymes are important in both the production of food (e.g., the fermentation of bread) and food spoilage.

• Function: Enzymes help break down food components such as starches, proteins, and fats. They also contribute to the ripening of fruits and vegetables and can be responsible for spoilage if they remain active after harvest or during storage.
• Action on Food: In the ripening process, enzymes can cause fruits to become soft or overripe. This is particularly problematic in fruits like bananas, avocados, and tomatoes, which can spoil quickly if not stored correctly.
• Control: The activity of enzymes can be controlled by temperature, pH levels, and the presence of inhibitors. For example, enzymes can be inactivated by refrigeration, freezing, or by applying heat (e.g., blanching vegetables before freezing).

Growth Conditions for Microorganisms and Enzymes

Both microorganisms and enzymes need specific conditions to grow and function properly. These conditions can be manipulated to prevent food spoilage:

    Temperature:

• Microorganisms and enzymes both have an optimal temperature range. For microorganisms, temperatures between 5°C and 63°C are ideal for growth (danger zone). Above 63°C, most microorganisms are killed, and below 5°C, growth is slowed or halted. Enzymes also have specific temperature ranges, with higher temperatures often speeding up enzyme activity until they become denatured (lose their shape and function).

    Moisture:

• Both microorganisms and enzymes need moisture to function. Dehydrating food or reducing moisture can slow or prevent microbial growth and enzyme activity. Drying, salting, and freezing are common methods of preserving food by reducing moisture.

    pH:

• The pH of the environment can affect both enzyme activity and microbial growth. Many bacteria, especially harmful ones, thrive in neutral pH environments (around 7), while yeasts and moulds grow best in slightly acidic conditions. Enzymes also have an optimal pH range that varies depending on the type (e.g., stomach enzymes work in an acidic environment, while others work in neutral or alkaline conditions).

    Oxygen:

• Many microorganisms, such as bacteria, need oxygen to grow (aerobic bacteria), while others can grow in the absence of oxygen (anaerobic bacteria). The presence or absence of oxygen can be manipulated in food storage to control microbial growth.

Control of Food Spoilage

To prevent or slow down food spoilage caused by microorganisms and enzymes, various methods of control are used:

    Temperature Control:

• Refrigeration (below 5°C) and freezing (below -18°C) are effective in slowing down or stopping microbial growth and enzyme activity. Cooking foods to temperatures above 75°C can kill most harmful microorganisms.

    Preservation Methods:

• Canning: Using heat to kill microorganisms and then sealing food in airtight containers.
• Salting: Removing moisture from food, which prevents the growth of microorganisms.
• Drying: Reducing moisture content in food, which inhibits microbial growth.
• Pickling: Using vinegar (acidic environment) to prevent bacterial growth.
• Use of preservatives: Chemical preservatives (e.g., ascorbic acid, sodium benzoate) can prevent the growth of microorganisms.

    Hygiene Practices:

• Practising good food hygiene, such as hand washing, cleaning surfaces and equipment, and preventing cross-contamination, can significantly reduce the risk of foodborne illness and spoilage.

By understanding microorganisms and enzymes, and how to control the factors that contribute to food spoilage, food safety can be better managed in preparation and storage.