Signs of Food Spoilage

This section explains the signs of food spoilage. Food spoilage refers to the process where food becomes unsuitable for consumption due to changes in its appearance, smell, texture, and taste. Spoilage is often caused by microorganisms such as bacteria, yeasts, and moulds, or by enzymic action. The signs of food spoilage can vary depending on the type of food and the cause of spoilage, but some common signs include:

    Change in Appearance:

• Discolouration: Foods may change colour, such as fruit turning brown due to oxidation or the growth of moulds on surfaces.
• Mould Growth: A visible fuzzy or powdery layer may form on the surface of food. Moulds can appear in colours such as green, black, or white.
• Softening and Sliminess: The texture of the food may become soft or slimy, particularly with fruits, vegetables, and meats.

    Off Odours:

• Spoiled food often develops unpleasant, sour, rancid, or rotten smells. This is a result of the breakdown of proteins, fats, and carbohydrates by microorganisms or enzymes.

    Changes in Texture:

• Food may become mushy or slimy due to microbial or enzymic activity. For example, meat may become soft and lose its firmness, while fruits may become overly soft or wrinkled.

    Tasting Unpleasant:

• The taste of spoiled food is often bitter, sour, or rancid. This happens when microorganisms or enzymes break down the components of the food, creating undesirable by-products.

Enzymic Action in Food Spoilage

Enzymes are biological catalysts that speed up chemical reactions. In food, enzymes are naturally present and can contribute to spoilage, even in the absence of microorganisms. Enzymic action is responsible for various changes in food, especially during ripening, but it can lead to undesirable effects if not controlled.

    Role of Enzymes in Food Ripening:

• Enzymes are involved in the natural ripening process of fruits and vegetables. For example, enzymes break down starches into sugars, soften cell walls, and alter the flavour and aroma of the fruit.
• Example: In bananas, the enzyme amylase breaks down starch into simpler sugars, causing the fruit to soften and change colour as it ripens.

    Enzymic Browning:

• One of the most common forms of enzymic spoilage is enzymic browning, which occurs in fruits like apples, pears, and bananas when they are cut or damaged.
• This happens when the enzyme polyphenol oxidase (PPO) reacts with oxygen in the air and causes phenolic compounds in the fruit to oxidise, resulting in brown spots.
• Control: To prevent enzymic browning, fruits can be treated with ascorbic acid (vitamin C) or citric acid, which inhibit the enzyme. Alternatively, keeping the fruit in an airtight container or at lower temperatures can slow down this process.

    Texture Changes:

• Enzymes can also cause a breakdown in the texture of food. For example, enzymes like pectinase break down pectin in fruits, causing them to soften. While this is a natural part of ripening, it can lead to spoilage if the fruit becomes overripe.
• Example: Enzymatic breakdown of proteins in meat can cause it to become overly soft or mushy.

    Rancidity of Fats:

• Enzymes such as lipase break down fats in food into free fatty acids and glycerol. This process is known as rancidity, which causes off-flavours and smells. It is particularly common in fatty foods like nuts, oils, and meat.

Mould Growth

Moulds are fungi that grow on food, often as a fuzzy or hairy layer. They reproduce by releasing spores, which can spread and lead to further contamination. Moulds can grow on a variety of foods, including bread, cheese, fruit, and vegetables.

    Conditions for Mould Growth:

• Moulds grow best in warm, moist environments. They also need a food source, such as organic material (e.g., bread, fruit, or cheese).
• Temperature: Moulds typically thrive at room temperature, but they can also grow in refrigerators, particularly on moist food.
• Moisture: High moisture content in food supports mould growth. Dry foods, on the other hand, are less likely to develop moulds.
• Air: Moulds need oxygen to grow, so foods stored in airtight containers are less likely to develop mould.

    Appearance of Mould:

• Mould often appears as a fuzzy or velvety coating on the surface of food. It can be green, black, white, or even blue, depending on the type of mould.
• Example: Bread is particularly susceptible to mould, often developing green or blue moulds if left out in a warm, moist environment for too long.

    Health Risks:

• Some moulds produce mycotoxins, which are toxic and can cause foodborne illness. Eating food contaminated with toxic mould can lead to symptoms like nausea, vomiting, and diarrhoea, or more serious health issues in extreme cases.
• Example: Moulds on bread or cheese may not always be harmful, but moulds on certain grains, nuts, and fruits can produce harmful mycotoxins.

    Control of Mould Growth:

• To prevent mould growth, store food in dry, cool environments and ensure it is properly sealed.
• Refrigeration: Keeping perishable items like fruit and dairy products in the fridge can slow down mould growth.
• Freezing: Freezing food can prevent the growth of mould, although it may not kill existing mould spores.
• Use of preservatives: Some food products contain preservatives, like sodium benzoate, which inhibit mould growth.

Yeast Action

Yeasts are a type of fungus that can cause both desirable and undesirable changes in food. Yeasts are used in the production of food products such as bread, beer, and wine through the process of fermentation. However, under certain conditions, yeast can also cause food spoilage.

    Fermentation by Yeasts:

• Yeasts, such as Saccharomyces cerevisiae, are used in food production to ferment sugars into alcohol and carbon dioxide.
• Example: In bread making, yeast ferments the sugars in the dough, producing carbon dioxide, which causes the dough to rise. The alcohol produced during fermentation evaporates during baking.

    Yeast Spoilage:

• Yeasts can also cause spoilage in foods, especially in high-sugar environments such as fruit juices, syrups, and jams. When yeast ferments sugars in these foods, it produces alcohol and carbon dioxide, which can lead to a sour or fermented taste.
• Example: Fruit juices left open or in warm conditions can ferment and develop an unpleasant taste and smell due to yeast activity.

    Conditions for Yeast Growth:

• Yeasts grow best in warm, moist environments, typically between 20°C and 30°C. They require a food source, usually sugar, to grow.
• Example: Yeast can grow in sugary foods like jams, fruit juices, and syrups if stored at room temperature or in warm conditions.

    Signs of Yeast Spoilage:

• The signs of yeast spoilage include bubbling (due to the production of carbon dioxide), off-odours (like a sour or alcoholic smell), and a change in texture or appearance (such as frothing on the surface of the food).

    Control of Yeast Growth:

• Refrigeration: Storing food containing yeast in the fridge can slow down or stop fermentation.
• Pasteurisation: Heating liquids, such as fruit juices or wine, to a high temperature can kill yeast and prevent fermentation.
• Proper Sealing: Ensuring that food is stored in airtight containers can prevent yeast from getting access to oxygen, reducing the likelihood of fermentation.

By understanding the signs of food spoilage, enzymic action, and the roles of moulds and yeasts, it becomes possible to better manage food safety and prevent the growth of harmful microorganisms and enzymes. Proper handling, storage, and hygiene are key to preserving food quality and ensuring it remains safe to eat.