Food preservation

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Food preservation

• F.6 Chemical Project

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Content

• 1.Introduction
• 2.The need to preserve food
• 3.Main principles of food
  preservation
• 4.Technical principles of food
• preservation
• 5.Common techniques of food
  preservation

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If there is no food preservation,

• Then...

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(No Transcript)
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The Total World Food Supply
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The Need to Preserve Food

• Food spoilage owing to microbial activities
• Caused by yeasts,fungi or bacteria
• either toxic in nature or produce toxic chemical
• eg.bread mould
• Food spoilage owing to chemical changes
• Oxidation of glycerides-gt peroxide
• Oxidation of phenols-gt browning of apple

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Food Spoilage
Reasons Microbial activities caused by yeast,
fungi, bacteria etc.. Chemical and biochemical
changes in food
How do the micro-organisms spoil the food? The
micro-organisms are toxin in nature. They produce
toxin chemicals when they act on the food.
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Examples of micro-organisms that spoiled
food Mould on bread Lactic acid bacteria in the
souring mild Clostridium botulinum on meat.
Principles of browning of apple The phenols in
apple is oxidized into diquinounes The
diquinones will undergo polymerization and
finally a brown products were formed
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Main Principles of Food Preservation

• 1.Killing of micro-organisms
• -micro-organisms found everywhere
• -rapid growth in damp warm environment
• -Produce toxic substances ,harmful to man
• 2.Inhibition of microbial growth
• -reproduce by simple cell division
• -necessary to keep food in conditions that are
  not favourable for microbial growth

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• 3.Retardation of chemical or biochemical changes
• -food undergo chemical or biochemical in storage
  even the absence of micro-organisms
• -Removal of air or water from food, and the
  inhibition of enzyme activities are common
  methods used to read the chemical or biochemical
  changes in food.

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Technique Principles of Food Preservation
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Changing of pH Value
Providing a favourable condition for the growth
of micro-organisms Advantages of increasing or
decreasing the pH value Extreme pH condition will
inhabit the growth of the micro-organism Examples
The use of vinegar in pickling ,use of lactic
acid in yogurt
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Use of Osmotic Process
Since the micro-organism require a minimum a
moisture content of 20 to growth Decreasing the
moisture content inside the cells by increasing
the solute concentration of food,would inhabit
the microbial growth PrincipleWater potential of
the micro-organism is higher than that in the
surroundings ,as water flow from higher water
potential to lower water potential ,the cells run
dry AdvantagesMicro-organism would not capable
to grow ExamplesPutting the food into
concentrated salt or sugar solution
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Removal of Moisture
Providing a favourable conditions microbial
growth in food and leading to hydrolytic reaction
during which food is spoiled. Advantages of the
removal of water Slowing down the microbial
growth rate.Suppressing chemical and biochemical
changes . ExamplesDrying and dehydration
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Altering Temperature
Providing a favourable condition for microbial
growth in food Advantages of decreasing
temperature Retarding the growth of
micro-organism Advantages of increasing
temperature a.Destroying the bacterial cells and
the spores b.Killing the micro-organisms
ExamplesHeat treatment,freezing
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Use of the Chemical Additives
Since many chemicals can inhabit the microbial
growth,the use of chemical , such
as Anti-oxidant can be used to reduce the
amount of dissolved oxygen in food .It can
retard the chemical and biochemical changes
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The Techniques of Food Preservation
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Heat Treatment
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Principle Heat kills micro-organisms, destroys
enzyme activity of micro-organisms in food.
Length of storage It depends on the heat
treatment and upon the type of food
Changes in quality The quality of food is
maintained
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Drying and dehydration
E.g. the dried food products such as biscuits,
vegetables, fruit, fish,shrimp and milk
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Principle Water is unavailable for reactions to
occur, and for micro-organisms to grow.
Length of storage This varies with the product,
storage conditions and the final moisture content
Changes in quality Often the reconstituted or
rehydrated food is comparable to fresh food
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Irradiation
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Principle Radiation destroys enzymes and
micro-organisms inside the food
Length of storage It significantly increases the
storage of any food in comparison to its
preservation by conventional methods
Changes in quality Nutrient destruction is no
greater than hat by conventional methods
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Refrigeration
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Principle Chilling slows down microbial
activities and chemical changes resulting in
spoilage
Length of storage After which time undesirable
off- flavours slowly develops
Changes in quality Freezing promotes the
retention of nutrients and does not destroy
nutrients
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Sugaring
In jam, fruits in heavy sugar syrup.Food is kept
in a strong sugar solution.
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Principle Water available for enzyme action and
microbial growth is removed by osmosis.
Length of storage When properly bottled or
canned, these fruits may be stored a year or
more.
Changes in quality these foods contain more
calories than fresh fruit.
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Salting
Salt Fish
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Principle Water essential for enzyme action and
microbial growth is removed by osmosis.
Length of storage Most product can be stored
three weeks to several months.
Changes in quality Its greater the loss in food
value, including loss of vitamins and minerals
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Canning
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Principle Cooking destroys enzymes and
micro- organisms.
Length of storage It can keep well for more than
one year when properly canned
Changes in quality 1. Colour and texture often
different from fresh product 2. No practical
effect on proteins, carbohydrates and fats 3.
Vitamin C and B are often destroyed.
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Pickling in Vinegar
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Principle Most micro-organisms do not grow well
in acidic solutions
Length of storage Picking alone is not enough
for long term storage.
Changes in quality It adds an appealing flavour
to the food
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Meat-curing
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Principle Sodium chloride ties up the water
otherwise used as a growth medium by
micro-organism
Length of storage It mainly depends on the
amount of chemicals used and the food product.
Changes in quality The quality of food is
generally maintained
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Use of food additives
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Principle The added substances inactivate or
kill micro-organisms, retard chemical spoilage.
Length of storage It depends on the nature of
chemical used and the formed product.
Changes in quality Quality is maintained or
enhanced.
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The End