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Food Spoilage & Preservation
Transcript of Food Spoilage & Preservation
- When foods are spoilt their original nutritional value, texture, and flavour are damaged, They become harmful to people and/or they become unsuitable to eat. Why do foods spoil? Causes of Food Spoilage Food spoilage is caused by the action of three main catalysts Moulds Yeast Bacteria Enzymes Food Preservation Sun-drying Sugar Preservation Earliest Methods Food Preservation Recent Methods of Food Preservation Irradiation Shell life Perishable Foods Non-perishable foods Semi-perishable foods Shelf life is the length of time that foods, beverages, pharmaceutical drugs, chemicals, and many other perishable items are given before they are considered unsuitable for sale, use, or consumption. Perishable foods are foods like fresh meat, seafood, and ripe fruits, they are foods that can decay.
examples include; They are foods that do not spoil or decay.... for example; canned goods, all pasta types, sugar, flour, curls (and chips if air-sealed), spices are non perishable as well.
- Semi-perishable foods are those that do not require refrigeration, but still have a limited shelf life. They include potatoes, onions, pumpkins and salamis.
-These items are usually kept on shelves in the storeroom complex, where they get plenty of air circulation around them.
- They have low water content a. Micro-organisms
c. Foreign Infestation (commonly insects) Micro-organisms The micro-organisms responsible for food spoilage are moulds, yeast and bacteria. Yazmin Velarde by 10 Red - They are microscopic fungi that live on plant or animal matter.
- They grow from tiny spores that float around in the air.
- When some of these spores fall onto a piece of damp food, they grow into mould. The mould feeds itself by producing chemicals that make the food break down and start to rot.
- As the food rots, the mould grows and becomes even more visible.
- Most moulds are not harmful, but a relatively small proportion of the moulds, found on foods are capable of producing toxic materials
- Easily destroyed by heating and high temperatures. mould on bread mould on tomatoes - Yeasts are tiny living organisms which are not visible to the naked eye, but which can be seen through the microscope.
-They multiply very fast and they react on certain components of foods like fruit juices, syrups etc. This reaction is called yeast fermentation.
- During yeast fermentation, the sugars present in the food are broken up to form alcohol and carbon dioxide. For this reason, yeast is useful for producing bread, yogurt, cider, and alcoholic beverages
- There is also a type of yeast (called false yeast) grows as a dry film on a food surface, such as on pickle brine. False yeast occurs in foods that have a high sugar or high acid environment.
- Like moulds, yeast easily dies when exposed to high heat.
- Can be bought either dried or fresh. dried yeast fresh yeast - are round, rod or spiral shaped living microorganisms.
- Bacteria, ike all living cells, give off waste products. It is these waste products that make food spoil as the bacteria reproduce and use the food for their own needs. The waste products of the bacteria, which are on a molecular level, can often be toxic, , which when eaten can cause food poisoning.
- They also vary in their requirement for food, moisture, acidity, temperature and oxygen. Bacteria can grow and develop rapidly between 20°C and 53°C
- Bacteria generally prefer low acid foods like vegetables and meat coccus bacteria bacili spirillae A). food spoilage caused by Enzymes B). food spoilage caused by (chemical reaction catalysts) = they are basically organic living cells that can activate chemical reactions.
= Food spoilage due to the chemical reactions as in cutting apples; it becomes brown while tomato cause develops a black scum.
= Enzymes are sensitive to heat and are easily destroyed by heat. They can act from 0°C to 60°C. All enzymes are inactivated by temperatures above 80°C.
Therefore, enzyme activity can be prevented by heating foods to temperature which inactivate the enzymes. It can also be prevented by cooling (as in freezing and refrigeration) by elimination of air, by protection from light and by addition of anti-oxidants. Foreign Infestation (Spoilage by Insects) A). food spoilage caused by Spoilage by Insects Worms, bugs, weevils, fruit flies, moths cause extensive damage to food as they carry bacteria which causes food contamination.
They reduce the nutritional value of food and make it unfit for human consumption. a fruit fly on a banana enzymes causing apple to brown black scum on tomatoes also caused by enxymes - Food preservation is the process of treating and handling food to stop or greatly slow down spoilage - Usually involves preventing the growth of micro-organisms that cause food spoilage (moulds, yeast, and bacteria,),
- Many methods of food preservation also involve retarding the oxidation of fats which cause rancidity. - The most common methods include drying, smoking, salting, and many others that have been used by the earliest cultures. drying chillies smoking fish - It is one of the most ancient food preservation techniques,
- In early cultures it usually involvesd spreading harvested fruit and vegetables on racks and allowing the sun to dry them.
- This process reduces water activity sufficiently to prevent bacterial growth, (since bacteria requires sufficient moisture to grow rapidly) and therefore preserving the food examples of usual sun-dried foods are sultanas currants apricots Salting - Salting is the preservation of food with dry edible salt.
- Salting is used because most bacteria, fungi and other potentially pathogenic organisms cannot survive in a highly salty environment, because the salt will draw out the moisture and dehydrate the bacteria present the food being salted. examples of foods that usually undergo this process: runner beans ham herring fish - Sugar preservation is very common method used to preserve fruits, where canned or bottled fruit is preserved in a syrup of sugar and water or fruit juice,
- If the fruits are rolled in sugar, they are called crystallied fruits. This is where the preserved material is cooked in sugar to the point of crystallisation and the resultant product is then stored dry.
- A modification of this process produces glace fruit (i.e. glace cherries) where the fruit is preserved in sugar but is then extracted from the syrup and sold, the preservation being maintained by the sugar content of the fruit and the superficial coating of syrup. examples of foods preserved by this method strawberry jam orange marmalade glace cherries - Is a recent method of food preservation that involves ionising gamma rays from a radioactive source to destroy the moulds and bacteria that cause spoilage.
- The rays pass through the food just like microwaves in a microwave oven, but the food does not heat up to any significant extent. Exposure to gamma rays does not make food radioactive.
- Used to inhibit the sprouting of potatoes and onions
- Used to prolong the shelf life of soft tropical fruits, spices, and seafood.
- To date, in Australia and New Zealand, only herbs and spices, herbal infusions and some tropical fruits are approved for irradiation mangoes papayas litchis/lychees examples tuna chicken steak flour sugar spices The End examples include potatoes nuts onions