Learn about Safe Food Production
Note that each module in the Qualification - Foundation Diploma in Food Production and Safety is a short course in its own right, and may be studied separately.
Learn to be Safe with Food
Anyone who works with food needs to understand how to keep it safe. When food deteriorates, it can become dangerous to eat.
Microscopic organisms are one of a number of things that can cause food spoilage. Food spoilage from these microorganisms is dependent on the ability of these microbes to grow and multiply. This is in turn affected by a range of factors such as water, pH, oxygen and temperature as well the physical structure of the food itself. Foods that spoil most rapidly are those that are moist, of neutral pH, are unrefrigerated, and ground or sliced. In contrast dry, acidic and refrigerated foods are more resistant to spoilage. Following we discuss how these factors affect food spoilage.
PH is a measure of how acidic or alkaline something is. Environments that are acidic have a pH below 7 and environments that are alkaline have a pH over 7. Microorganisms tend to thrive at a neutral pH of between 6.6 and 7.5 whereas most bacteria are inhibited at a pH below 4, although yeast and moulds can tolerate lower pH levels.
Water is an important constituent of all foods and even relatively dry foods such as bread and cheese contain over 35% water. Generally lack of water inhibits microbial growth. Bacteria in particular are unable to grow and multiply in dry environments. This is why drier foods are most likely to be spoiled by yeast and mould which can survive in slightly drier environments. Availability of water is affected by drying foods and by adding salt or sugar to foods
Oxygen can cause food spoilage by enhancing the action of food spoilage microorganisms as most microorganisms require oxygen to grow and multiply. Oxygen also aids the action of the enzymes involved in food spoilage and is capable of causing oxidative damage to foods by itself e.g. causing oxidative damage to the fat portion of food causing foods to have a strong smell and taste rancid.
Structure of food
Cutting, chopping, shredding or grinding foods increases the surface area of foods producing a greater surface area for microbial growth. The presence of an outer covering on food such as the skin on fruit and vegetables acts as a barrier to microbes. When cut through any of these processes, that protective barrier is removed. This is why fruits such as lemons last longer when they are whole and covered in rind rather than when they have been sliced.
Foods can also have natural protection from microorganisms e.g. cranberries produce benzoic acid which has antifungal properties and egg whites contain lysozyme which has antibacterial properties
Reducing food spoilage by microorganisms
An understanding of the causes of food spoilage can help to suggest interventions to prevent spoilage occurring. Here are some factors to consider:
1. Cover food or pack foods carefully to prevent the invasion of microorganisms. Also remove spoiled foods that are close to unspoiled foods to prevent cross contamination and remove any microorganisms present on foods for example by washing salad vegetables.
2. Lower the temperature a food is stored in to prevent microbial growth. Optimal temperatures are below 5oC for refrigerated foods and below -180C for frozen foods (although freezer temperatures can range from -26°C to -0°C.
3. Reduce the availability of oxygen to foods by using appropriate food production methods and packaging which minimises the oxygen available to foods. Also consider adding antioxidants to food where appropriate as these help to absorb oxygen and slow down the rate of oxidation, examples of antioxidants include vitamin C and vitamin E.
4. Consider adding preservatives to foods such as salt, sugar and vinegar, which are natural preservatives, and sodium chloride and citric acid which are chemical preservatives.
5. Reduce physical damage of foods by handling foods carefully e.g. taking care when picking fruits and vegetables and taking care when packing and transporting foods.
6. Kill microorganisms present in foods e.g. by cooking foods appropriately and pasteurising foods. However, sometimes this aspect of food preservation can be a balance between killing microbes and producing a quality food product, as processing that kills all the microorganisms in a food can also affect the taste, texture and nutritional content of a food.
7. Increase the acidity of food e.g. by adding an acid such as acetic acid.
Food Spoilage by Enzymes
Enzymes are catalysts in living cells which are capable of speeding up or slowing down a chemical reaction without being altered by the reaction itself. Enzymes are a natural constituent of food and they are also released by bacteria which invade food to allow them to obtain nutrients from the food. Enzymes themselves catalyse a wide variety of functions in plants and animals. In relation to foods, enzymes can help to control ripening and changes in the flavour, texture, nutritional content and colour of different foods.
The action of enzymes has had benefits to food manufacture. Examples of enzymes used in the food industry include proteases which are used to help tenderise meat, lipase which helps provide flavour to foods such as chocolate and cheese, and amylase which converts starches to sugars in industries such as brewing and baking.
Unfortunately, enzymes also have a negative side as they start to degrade food causing spoilage e.g. enzyme reactions cause the blackening of foods such as apples and bananas. Enzymes specifically linked to food spoilage include lipase, which causes cereals to discolour and promotes hydrolytic rancidity in milk and oils; ascorbic acid oxidises which causes the destruction of vitamin C in vegetables; pectic enzyme which promotes the softening and browning of fruits; and protease which leads to a reduction of gluten formation in flour.