Topic 2: Part B Flashcards
Food processing
conversion of raw plant and animal tissue into convenient and practical forms for consumption
Basic principles of food processing to achieve preservation include
- moisture removal
- heat treatment
Moisture removal
removing biological active water in an attempt to stop microorganism growth
Heat treatment
pasteurization, blanching, canning, baking, cooking, sterilization
Low temp treatment
cold storage
Acidity control
controlling pH of the food by adding an acidulate
Traditional non thermal processing
through chemical additives or food processing
Non thermal processing innovations
irradiation, high pressure
Food processing aids
specific food additives like gums, natural colouring agents, enzymes and sweeteners
Food spoils because of
microbiological, chemical, physical or enzyme induced decay
Decrease in food losses is achieved mainly by..
food preservation and food additives
Food preservation is the use of specific processing techniques to…
reduce spoilage microorganisms in food to improve safety and shelf life
Biologically active water in tissues is one of the;;
primary causes of food spoilage.
Food with a high aw.. and foods with low aw..
- deteriorate quickly,
- can be stored for extended periods
Other major causes of spoilage
- biological changes: growth of microorganisms
- chemical changes: oxidation or enzyme reactions
- physical changes: separation of water and oil that can occur in foods like mayo/yougurt as they age
3 main classes of food preservation
- chemical: addition of salt, sugar or chemical preservation
- biological: fermentation
- physical: drying, heating, cooling, irradiation
Chemical food preservation
addition of sugar, salt, or chemical preservatives to reduce food spoilage. salt and other preservatives such as potassium sorbet lower the water activity in foods.
Preservatives
additives that maintain the freshness of a food
Biological food preservation
fermentation lowers the pH of the food product, resulting in taste changes. encourages growth of friendly bacteria which can inhibit growth of pathogenic bacteria.
Salt or vinegar may be added to control…
bacterial growth during fermentation
Fermentation
preservation technique that involves bacteria or yeast acting on the carbohydrates of a food
Physical
- drying
- thermal processing
- cooling
- irradiation
Drying
involved removal of water form the food. the food is preserved because of microorganisms cannot survive in dry habitat. in ancient times drying was done predominantly by sun
4 ways of drying
- oven/plate drying
- spray drying
- drum drying
- freeze drying
Problems with drying by heat
- loss of heat sensitive nutrients such as vitamin C, riboflavin and niacin
- can alter sensory properties (colour, texture, etc)
Oven/plate drying
food spread on slatted floor or on shelves inside kilns or dying rooms. hot air is blown over and through the food. can also be placed on trays that travel through tunnel of hot air. the high temp removes the moisture form the food and often the moisture from the air by creating a vacuum environment
Drum drying
- Food is evaporated
- Concentrated product poured over large heated drums that keep rotating and get coated with more and more food product
- The thin layer of the food product on the heated drum dries very quickly into thin layers.
- These layers are further ground to obtain powders.
- example is mashed potatoes. NOT good for milk
Spray drying
spray nozzle sprays tiny droplets of liquid into chamber and the high temp immediately dries these droplets. by the time the droplets get to the bottom of the chamber they are dried and collected. vacuum ensures constant removal of moisture to speed drying process. milk powder dried by this method has better solubility. (coffee, egg whites)
Freeze drying
food is first frozen then placed in vacuum where ice is evaporated via sublimation. most effective method of drying because food isn’t exposed to high heat (more vitamins intact) but expensive
3 pretreatments used
- physical
- blanching
- chemical
Physical pretreatments
some fruits have their skin exposed to lye or hot water to crack skin before drying. shortens drying time and improves texture of end product
Blanching pretreatments
quick exposure to heat. used for fruits or veggies. pre treatment in freezing or drying. main purpose to inactivate enzymes that affect colour and texture and decrease oxidative degradation of the food.
Chemical pretreatments
some veggies and fruits are dipped in sulphite solution or exposed to sulphur dioxide gas before drying to prevent growing and to protect against loss of vitamin a and C. can destroy thiamin, may cause allergic reactions
