Wednesday, 17 August 2011

Food spoilage By Sempiri Geoffery

Food spoilage
By Sempiri Geoffery
Food spoilage can be defined as the deterioration a food product in the color, flavor, odor, or consistency. Food deterioration can either be a result of the growth of microorganisms, and/or the Chemical action i.e. enzymes and oxidation.
Food spoilage can also be defined as anything that affects the appearance, texture, smell, and taste of a food. It is caused by spoiling microbes that reproduce on the food and break it down.
There fore Food spoilage means the original nutritional value, texture, flavor of the food are damaged, therefore unsafe for Human consumption. Food spoilage can be microbial i.e. spoilage due to growth of yeasts, bacteria or moulds in food or chemical i.e. due to enzymatic activities, and oxidation
Microbial spoilage;
Three types of microorganisms cause food spoilage namely; yeasts, moulds and bacteria.
  1. Yeasts growth causes fermentation which is the result of yeast metabolism. Yeast can metabolizes sugar producing alcohol and carbon dioxide gas. This is known as fermentation.  The fermentation process is some times useful in processes like beer and wine Making, only that it is controlled fermentation i.e. a know strain of yeasts is used.
  2. Moulds grow in filaments forming a tough mass which is visible as `mould growth'. Moulds form spores which, when dry, float through the air to find suitable conditions where they can start the growth cycle again.  Mould can cause illness, especially if the person is allergic to molds. Usually though, the main symptoms from eating mouldy food will be nausea or vomiting from the bad taste and smell of the mouldy food.
Both yeasts and moulds can thrive in high acid foods like fruit, tomatoes, jams, jellies and pickles. Both are easily destroyed by heat. Processing high acid foods at a temperature of 100°C (212°F) in a boiling water canner for the appropriate length of time destroys yeasts and moulds.
Examples of Fungal Spoilage Include;
  • Storage rots in strawberry caused by Botrytis cinerea.
  • Black mummy rot of grapes caused by Guignardia bidwellii
  • Blue mould rot in tomato caused by Penicilliumi spp and  Fusarium spp.
  • Watery soft rot in apple caused by Sclerotinia sclerotiorum.
  • Blue mould on oranges caused by Penicillium digitatum.
  • Storage rots in grapes caused by Botrytis cinerea.
  1. Bacteria; Spoilage bacteria are microorganisms (too small to be seen with our naked eyes, without a microscope) that cause food to deteriorate and develop unpleasant odors, tastes, and textures. Bacteria can be round, rod or spiral shaped one-celled microorganisms. Bacteria can grow under a wide range of conditions. Bacteria can be spore-forming or nonspore-forming. They cause fruits and vegetables to get mushy or slimy, or meat to develop a bad odor because they generally prefer low acid foods.  Example of bacterial spoilage can be Soft rot in tomato caused by Erwinia carotovora.
In order to destroy bacteria spores in a relatively short period of time, low acid foods must be processed for the appropriate length of time at 116°C (240°F) in a pressure cooking. Temperatures higher than 100°C [212°F] can be obtained only by pressure cooking.
It is highly advisable not to choose to eat spoiled food. This is because eating spoiled food caused by bacteria can cause food poisioning due to presences of Pathogenic bacteria.

They grow rapidly in the "Danger Zone" – the temperatures between 40 and 140 °F – and do not generally affect the taste, smell, or appearance of food. Food that is left too long at unsafe temperatures could be dangerous to eat, but smell and look just fine. E. coli O157:H7, Campylobacter, and Salmonella are examples of pathogenic bacteria.

Chemical Spoilage;
  1. Enzymatic Spoilage
Enzymes are proteins in nature and are found in all plants and animals. If uncooked foods are not used immediately, enzymes can cause undesirable changes in color e.g. enzymatic browning of peeled cooking bananas and apples, texture and flavor. Enzyme activity is easily stopped by heat processing. Heating denatures enzymes. Freezing does not stop enzyme activity, but it effectively retards it, particularly at temperatures below 0°F (-18° C).
  1. Oxidative Spoilage
Atmospheric oxygen can react with some food components which may cause rancidity or color changes especially in fatty foods. In fresh vegetables or fruits, oxygen is absorbed by the product and acts to ripen it or carry out other changes. In other materials like the fats in meat or the oils in nuts, oxidation occurs and contributes to rancidity. Oxidation reduces rapidly as temperatures are lowered, but continues at below-freezing temperatures.
Others include;
  • Insect Spoilage
Insects and rodents can also cause food spoilage especially in stored cereals and grains. Infestations by insects and rodents, account for a very big percentage of losses in cereal and grain foods in storage.  They cause off odors, and also eat up part of the food. Foods attacked by insects and rodents will have their remains such as skeletons and wings rendering them unacceptable.
  • Low temperature injuries
The internal structures of the food such fruits and vegetables can be damaged by exposure to very low temperature. E.g. chilling injuries and freezing burns in fruits and vegetables kept very low temperatures.

Some Simple Ways on How to Prevent Food Spoilage

  • Proper cooking of food i.e. proper temperature/time combination for your kitchen cooking
  • Always check the quality of the food products before buying-for example, if the vegetables/fruits are not fresh, don’t buy unless are for immediate use.
  • Expiration dates- Always read the expiry dates before buying any food item from a shop or supermarket. All foods should be labeled with an expiration date.
  • Refrigeration unit- If you own a refrigeration unit, a daily check should be done to ensure proper temperature regulation. The temperature should not exceed 41 degrees. When the food cools down, put it in the fridge if you are not going to eat it soon i.e. when you want it consumed the following day. Food in the fridge can last up to months if frozen.
  • Always let the food cool before covering it. If you cover a hot food, it will moist and produce water which may cause food spoilage.
  • Always wipe the container dry before putting the food.
  • Always use clean materials e.g. spoons when serving food. E.g. if you used spoon with your saliva can spoil the food.