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Food Spoilage

Food spoilage

A.4.1 Define food spoilage.

Food spoilage
Food becoming unfit for consumption, for example, due to chemical or biological contamination
  • PDF for topic A4 from msc-technology

A.4.2 Explain that food spoilage can be caused by physical spoilage, chemical spoilage or microbiological spoilage.

Physical damage to the protective outer layer of food during harvesting, processing or distribution increases the chance of chemical or microbiological spoilage.

Physical spoilage

  • Damage has occurred to the outer layer of food during production and distribution
  • Increases the chance of chemical or microbial spoilage.
  • Skin of the apple breaking or bread becoming stale

Chemical spoilage

  • Enzymes start to deteriorate the food such as breaking down the skin
  • Can lead to microbes entering and assisting the rotting
  • Rancidity

Microbiological spoilage

  • Microorganisms include moulds, yeasts and bacteria)
  • They continue to grow
  • Alter, flavour, texture and colour

Extra informational websites outlining the causes of food spoilage (physical, chemical, and microbiological)

Spoilage Spoilage
Mallard Browning Enzymic Browning

A.4.3 Explain that the two principal causes of chemical spoilage of food are enzymic spoilage and rancidity.

Chemical Spoilage

  • since it is a chemical reaction that occurs
  • that leads to rotting of food
  • Enzymic spoilage and rancidity.

A.4.4 Outline the changes that take place in enzymic spoilage.

Enzymes are proteins found in all plants and animals. If perishable and semi-perishable foods are not used while still fresh then enzymes ...

  • cause undesirable changes in colour, texture and flavour.
  • are destroyed by heat processing.

This link address enzymatic spoilage: enzymatic spoilage

A.4.5 Explain that enzymes are responsible for some browning reactions during food preparation.

Consider enzymic browning and Maillard reaction.

Maillard reaction

Chemical reaction with proteins and sugars when heated.
When meat is cooked the surface has the strongest flavours.

Enzymic browning

Chemical process of enzymes in fruits, vegetables and seafood
Causes the brown pigments to appear.
The peeling of an apple then left will start to brown (can be prevented by adding lemon juice)
Enzymic Browning Maillard Browning

A.4.6 Describe three types of rancidity, and outline how rancidity can be prevented.

Consider absorption, hydrolytic and oxidative rancidity.

Absorption rancidity

  • when lipids are stored near strong smelling foods or chemicals
  • making the food unpleasant

Hydrolytic rancidity

  • Enzymes react with the fats in the food
  • cause sharp, biting, acrid flavour

Oxidative rancidity

  • oxgyen comes in contact with the lipids
  • changes the flavour or odour of dairy products

Preventing rancidity

  • use of anti-oxidants which remove oxygen
  • Properly seal the food so oxygen contact is reduced

A.4.7 Explain the importance of rancidity in the shelf life of food products.

  • Understanding the speed or cause of hastening of rancidity
  • when food products are not protected
  • Preservatives need to be added to prolong shelf-life
  • Shelf life is increased

A.4.8 Define water activity (aw).

Water activity (aw)
The water in food that is not bound to food molecules, which can support the growth of bacteria, yeasts and fungi, and is measured on a scale of 0 (bone dry) to 1.0 (pure water).

More information concerning water activity

A.4.9 Describe the importance of water activity in microbial spoilage.

Microbial spoilage can be caused by bacteria, moulds and yeasts. Water activity of food is an important determinant of the type of food spoilage caused.
  • Without water bacteria, moulds and yeasts cannot grow.
  • Foods Aw as it relates to microbial spoilage

Food preservation

A.4.10 List the major reasons for preserving foods.

Consider extension of the safe storage life of food, safety, acceptability, nutritive value, availability and economic viability.

A.4.11 Describe five methods of preserving food, including chilling, irradiation (pasteurization, sterilization, canning), vacuum packing, use of acids and preservatives, and removal of water (dehydration, use of sugar and/or salt).

Irradiation Blast Chilling
Vacuum Package Dehydration
acids and preservatives Pasteurisation
Sterilisation, & Canning
use radiant energy


  • reduce the temperature of food
  • slows the bacterial growth
  • can be used on most foods
  • NB Freezing stops the growth


  • Ionising radiation, also known as irradiation.
  • Radiant energy contains wavelengths
  • That damage micro-organisms but not the food
  • NB Also ... "Broiling and toasting use low-level radiant energy to cook food" from above link.

Pasteurisation, Sterilisation, & Canning

  • using radiant energy
  • heats up the food
  • kills the micro-organisms

Vacuum packing

  • seal and remove air in a food package
  • micro-organisms cannot grow in a vacuum

Use of acids and preservatives

  • acid has preservative qualities
  • acid inhibits bacterial growth
  • an example is acetic acid (vinegar) in pickles.

Removal of water (dehydration use of sugar and/or salt)

  • The salt and sugar draws out moisture
  • Creates an environment that bacteria cannot live in

A.4.12 Explain how food preservation methods affect the organoleptic properties of foods.

Consider bread, fruit and milk.


  • is fermented and baked
  • changes the raw materials into something edible


  • add sugar and boil to make jam and jellies
  • sweetens the food


  • UHT processing
  • has a bitter flavour

A.4.13 Explain how food preservation methods affect the nutritional properties of foods.

Consider bread, fruit and milk.


  • the raw materials of flour, water, sugar, milk, and other raw materials
  • last longer because they have been preserved in the bread
  • improved access to nutrients


  • Depends on method
  • Canning and freezing maintain nutrient levels or minimal loss


  • UHT heating process
  • lose nutrients
  • often vitamins a added


Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.

Images are clickable links to its location.

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Page last modified on December 06, 2012, at 02:01 AM