How does spoilage take place

Food can be contaminated through the misuse or mistaken handling of chemicals, including pesticides, bleach and other cleaning materials. All chemicals detergent, disinfectant, sanitiser used in the food preparation area should be removed before food preparation begins, to prevent any chemical contamination of the food.

Physical contaminants include stones, pieces of glass, and metal. Physical contamination can occur at any stage of the food chain: for example, stones, bones, twigs, pieces of shell or foreign objects can enter food during handling and preparation. These materials should be removed, if possible, for example by sieving or picking out the items with clean fingers. Food spoilage is the process of change in the physical and chemical properties of the food so that it becomes unfit for consumption.

Food spoilage is any undesirable change in food. Most natural foods have a limited life: for example, fish, meat, milk and bread are perishable foods, which means they have a short storage life and they easily spoil. Other foods also decompose eventually, even though they keep for a considerably longer time. The main cause of food spoilage is invasion by microorganisms such as fungi and bacteria.

Microbial spoilage is caused by microorganisms like fungi moulds, yeasts and bacteria. They spoil food by growing in it and producing substances that change the colour, texture and odour of the food. Eventually the food will be unfit for human consumption. When food is covered with a furry growth and becomes soft and smells bad, the spoilage is caused by the growth of moulds and yeasts look back at Figure 8. Microbial spoilage by moulds and yeasts includes souring of milk, growth of mould on bread and rotting of fruit and vegetables.

These organisms are rarely harmful to humans, but bacterial contamination is often more dangerous because the food does not always look bad, even if it is severely infected. When microorganisms get access to food, they utilise the nutrients found in it and their numbers rapidly increase. Food spoilage directly affects the colour, taste, odour and consistency or texture of food, and it may become dangerous to eat. The presence of a bad odour or smell coming from food is an indication that it may be unsafe.

But remember that not all unsafe food smells bad. Food contamination is when food is contaminated with microorganisms or substances and eating it could result in foodborne disease. Food spoilage is any undesired change in the natural colour, taste or texture of food items that makes it unfit for consumption because it has lost its quality and nutritional value.

The term contact spoilage is used when microbial spoilage is the result of direct contact or touching between the food and any contaminated or unclean surface such as shelves, food preparation boards or unwashed hands. It also includes food-to-food contact, for example between cooked meat and raw meat or between rotting fruit and sound fruit.

Physical spoilage is due to physical damage to food during harvesting, processing or distribution. The damage increases the chance of chemical or microbial spoilage and contamination because the protective outer layer of the food is bruised or broken and microorganisms can enter the foodstuff more easily. For example you may have noticed that when an apple skin is damaged, the apple rots more quickly.

Chemical reactions in food are responsible for changes in the colour and flavour of foods during processing and storage.

Foods are of best quality when they are fresh, but after fruits and vegetables are harvested, or animals are slaughtered, chemical changes begin automatically within the foods and lead to deterioration in quality.

Fats break down and become rancid smell bad , and naturally-occurring enzymes promote major chemical changes in foods as they age. Every living organism uses specialised proteins called enzymes to drive the chemical reactions in its cells. After death, enzymes play a role in the decomposition of once-living tissue, in a process called autolysis self-destruction or enzymic spoilage.

For example, some enzymes in a tomato help it to ripen, but other enzymes cause it to decay Figure 8. Once enzymic spoilage is under way, it produces damage to the tomato skin, so moulds can begin to can attack it as well, speeding the process of decay.

When the cells of fruits and vegetables such as apples, potatoes, bananas and avocado are cut and exposed to the air, enzymes present in the cells bring about a chemical reaction in which colourless compounds are converted into brown-coloured compounds. This is called enzymic browning. If the food is cooked very soon after cutting, the enzymes are destroyed by heat and the browning does not occur. For example, apples are prone to discolouration if cut open when raw, but when cooked they do not go brown.

Spoiled food is generally more a problem of appearance than a problem of disease causing. In food spoilage, the changes in appearance or texture of the food, such as rottenness, softness and change in colour, taste or odour are usually obvious, whereas in contaminated food such characteristics may not be noticed. A large majority of the microorganisms responsible for food spoilage are not pathogenic to humans. However, you should advise people in your community that they should not eat food that is spoiled because it is not nutritious and may make them sick cause vomiting.

Finally, we turn to the factors that can increase or delay the process of food spoilage. They include its water content, environmental conditions, packaging and storage. The amount of water available in a food can be described in terms of the water activity a w.

The water activity of most fresh foods is 0. This means that they have a very high water content and can support a lot of microbial growth.

Meat is traditionally dried by adding table salt to it. Can you suggest why salting enables the meat to be stored for a long time? You will learn more about salting, smoking, refrigeration and other food preservation methods in Study Session The salt draws out water from the meat so the a W is reduced. This makes the conditions too dry for harmful microorganisms to multiply in the salted meat.

No matter whether food is fresh or processed, the rate of its deterioration or spoilage is influenced by the environment to which it is exposed. Changing the environment can help to delay spoilage.

For example, storing foods at low temperatures reduces spoilage because both microbial and enzymic decay is faster at higher temperatures. Packaging is a means of safeguarding food when it is raw, or after it has been processed or prepared.

It helps to protect food against harmful contaminants in the environment or conditions that promote food spoilage including light, oxygen and moisture. The type of packaging is a key factor in ensuring that the food is protected. Packaging of foods in cans, jars, cartons, plastics or paper also serves to ensure food safety if it is intact, because it provides protection against the entry of microorganisms, dust, dirt, insects, chemicals and foreign material. Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions.

You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module. The entry and development or multiplication of infectious agents in the body of humans or other animals. Transfer of harmful microorganisms or their microscopic stages eggs, larvae from one source to another. Using the following two lists, match each numbered item with the correct letter. You are asked by a school head teacher to explain to some students about food contamination by microorganisms.

Write a plan of what you will tell them, including explaining why microorganisms are dangerous and under what conditions they grow and multiply. Suppose you went to a village for a house visit and found complaints of foodborne illness among the villagers. What possible ways of food contamination do you suspect and how will you teach the villagers about them?

You might suspect that the food handlers who prepare and serve food have been infected and have transmitted the infection through food to healthy people. The food might have become contaminated with chemicals like pesticides during transport, storage and preparation, or there may have been accidental or deliberate chemical contamination of food items. Hence you should tell them how they can prevent their foods from any contamination by avoiding cross-contamination, using correct food storage practice, frequent handwashing by food handlers, thorough cooking, separating raw food from cooked food, and avoiding coughing and sneezing over food.

The two peppers look different because one has been spoiled by enzyme reactions, which have also allowed moulds to grow on the fruit.

Enzymes are important to the normal functioning of living cells, but after the pepper is harvested and stored autolytic enzymes begin to spoil it. In short this allows you to use the content throughout the world without payment for non-commercial purposes in accordance with the Creative Commons non commercial sharealike licence. Please read this licence in full along with OpenLearn terms and conditions before making use of the content.

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These creatures require food to survive and damage food, making it more vulnerable to further deterioration. Bruises and cracks on raw produce leave areas where microorganisms easily may grow. Improperly packaged foods, dented cans and broken packages provide places for microorganisms, air, light and creatures to enter. Gentle handling of food items will help maintain food quality and safety longer. Temperature affects storage time, and food deteriorates faster at higher temperatures.

Recommended temperatures for storage areas are:. Microorganisms, both spoilage and pathogenic, grow rapidly at room temperature. To slow microbial growth, the enzymatic and oxidation processes, store foods at lower temperatures. Read more about microorganisms and temperatures. Microorganisms need time to grow and multiply. Other reactions, such as oxidation and enzyme action, also require time to develop. Purchase reasonable quantities, especially of perishable foods, to help avoid long-term storage.