How do microorganisms spoil food?

Microorganisms spoil food by growing on it and breaking down its nutrients, which changes the food’s taste, smell, appearance, and safety. Warm and moist conditions encourage the growth of bacteria, fungi, and sometimes protozoa, which release enzymes and toxins that make food unfit for consumption. This is why perishable items like milk, bread, fruits, and cooked food spoil quickly if not stored properly.

1. Bacterial Spoilage

Bacteria such as Salmonella, E. coli, and Clostridium multiply rapidly in food. They decompose proteins and carbohydrates, producing foul odors, slimy textures, and toxins that cause food poisoning. For example, milk left outside turns sour due to lactic acid bacteria.

2. Fungal Growth (Moulds and Yeasts)

Fungi grow on bread, fruits, and vegetables when they are kept in damp places. Moulds appear as green, black, or white patches and release toxins called mycotoxins that are harmful to health. Yeasts ferment sugars in food, leading to sour taste and gas formation.

3. Food Poisoning and Contamination

Some microorganisms release harmful toxins in food, which may not always change its appearance but make it dangerous to eat. For example, Clostridium botulinum produces a toxin in improperly preserved canned food that can cause serious illness.

4. Visible Changes in Food

• Odor: Spoiled food often smells sour, rotten, or putrid.
• Texture: Sliminess, softness, or watery breakdown.
• Color: Growth of green or black mould patches, or discoloration of vegetables.
• Taste: Sour, bitter, or unusual flavors caused by microbial fermentation.