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Physical and chemical changes
during food spoilage
What is food spoilage?
• Food spoilage is the process of changing the physical and chemical
properties of the food so that it becomes unfit for consumption.
• Food spoilage is any undesirable change in food.
• Most natural foods have a limited life: for example, fish, meat, milk and
bread are perishable foods, which means they have a short storage life and
they easily spoil.
• Other foods also decompose eventually, even though they keep for a
considerably longer time.
• The main cause of food spoilage is invasion by microorganisms such as
fungi and bacteria.
Food
Food
deterioration Economic loss
Food spoilage
Food groups
Highly Perishable
Meat
Fruit
Milk
Vegetables
Eggs
Semi perishable
Potatoes
Nuts
Flour
Stable (non-perishable)
Rice
Dry beans
Classification of Foods on the Basis of
Stability
Food nutrients
Food
Vitamins
Proteins
Lipids
Human Growth
Energy
Building materials
Carbohydrate
Major causes of food spoilage
Physical
• Temperature
• R.H.
• Light
• Mechanical damage
Chemical
• Enzymatic reaction
• Non enzymatic reactions
• Rancidity
• Chemical interaction
• Bacteria
• Yeast
• Molds
Others
Microorganisms
• Insects
• Rodents
• Animals
• Birds
Spoilage
The food may become unacceptable due to the following factors:
1) Growth and activities of micro-organisms principally bacteria, yeasts and molds
(This is by far the most important and common cause of food spoilage).
2) Activities of food enzymes (enzymatic browning is a common example).
3) Infestation by insects, parasites and rodents.
Biological hazards
Types of Spoilage
4) Chemical changes in a food (i.e. not catalyzed by enzymes of the tissues or of
micro-organisms). For example the chemical oxidation of fats producing rancidity as
well as non-enzymatic browning reactions in foods like Maillard Browning.
5) Physical changes or damages such as those caused by freezing (freezer burn), by
drying (caking) etc.
6) Presence of foreign bodies.
Physical hazards
Chemical changes
Chemical changes in a food (i.e. not catalyzed by enzymes of the tissues or of micro-
organisms). For example the chemical oxidation of fats producing rancidity as well as
non-enzymatic browning reactions in foods like Maillard Browning.
Chemical reactions take place in the presence of atmospheric oxygen and sunlight.
Two major chemical changes, which occur during the processing and storage of foods,
are lipid oxidation and non-enzymatic browning which deteriorate sensory quality,
colour and flavour .
Chemical changes
Lipid oxidation is influenced by light, oxygen, high temperature and the presence of
iron and copper, and water activity. Control of these factors can significantly reduce the
extent of lipid oxidation or rancidity in foods.
Non-enzymatic browning is one of the major causes of deterioration which takes place
during frying, cooking, storage of dried and concentrated foods through Maillard,
caramelization and ascorbic acid oxidation.
Chemical changes
Maillard reaction occurs due to reactions between reducing sugars and amino acids in
the presence of heat and results in formation of black brown insoluble pigments.
Caramelization of sugars occurs in presence of high heat and low moisture content in
the food. Oxidation of fatty acids to other chemicals like aldehydes, ketones, alcohols
and esters also results in off-flavours.
Chemical changes
Maillard reaction occurs due to reactions between reducing sugars and amino acids in
the presence of heat and results in formation of black brown insoluble pigments.
1912. Louis Camille Maillard a
French physician and chemist
Chemical changes
Maillard reaction occurs due to reactions between reducing sugars and amino acids in
the presence of heat and results in formation of black brown insoluble pigments.
Chemical changes
Maillard reaction occurs due to reactions between reducing sugars and amino acids in
the presence of heat and results in formation of black brown insoluble pigments.
Chemical changes
Caramelization of sugars occurs in presence of high heat and low moisture content in
the food.
Chemical changes
lipid oxidation or rancidity in foods.
Chemical changes
RANCIDITY
Hydrolytic Rancidity Oxidative Rancidity
Hydrolytic Rancidity
Triacylglycerol Glycerol Free fatty acids
(Volatile bad odour)
Chemical changes
Oxidative Rancidity
Chemical changes
Ascorbic acid
Chemical name for vitamin C is ascorbic acid, it’s chemical formula is C6H8O6.
As the name says, ascorbic acid is an acid. This means it can release protons (H+) and
lower the pH of a water solution.
By lowering the pH of a solution, it becomes more sour. Once ascorbic acid has given
away/released its proton, the name changes to ascorbate.
This reaction is reversible though, when conditions permit the proton can sit back on
the ascorbate.
Chemical changes
Ascorbic acid oxidation
‘donation’ of two electrons (e–), ascorbic acid also releases two protons. This will result
in a new stable molecule: dehydroascorbic acid
Chemical changes
 Hydroxylation of monophenol to o-diphenol
 Dehydrogenation of o- diphenol to o-quinone
ENZYMATIC BROWNING Polyphenol
oxidase
Phenolic
substrate
O2
O2
O2
O2
O2
O2
O2
Phenolic
substrate
Polyphenol
oxidase
Physical changes
Physical changes or damages such as those caused by freezing (freezer burn), by
drying (caking) etc.
Freezer Burn
Freezer burn is a condition that occurs when frozen food has been damaged by
dehydration and oxidation, due to air reaching the food. It is generally caused by food
not being securely wrapped in air-tight packaging.

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2T. AGM Physical and chemical changes during food spoilage.pptx

  • 1. Physical and chemical changes during food spoilage
  • 2. What is food spoilage? • Food spoilage is the process of changing the physical and chemical properties of the food so that it becomes unfit for consumption. • Food spoilage is any undesirable change in food. • Most natural foods have a limited life: for example, fish, meat, milk and bread are perishable foods, which means they have a short storage life and they easily spoil. • Other foods also decompose eventually, even though they keep for a considerably longer time. • The main cause of food spoilage is invasion by microorganisms such as fungi and bacteria. Food Food deterioration Economic loss Food spoilage
  • 3. Food groups Highly Perishable Meat Fruit Milk Vegetables Eggs Semi perishable Potatoes Nuts Flour Stable (non-perishable) Rice Dry beans Classification of Foods on the Basis of Stability
  • 5. Major causes of food spoilage Physical • Temperature • R.H. • Light • Mechanical damage Chemical • Enzymatic reaction • Non enzymatic reactions • Rancidity • Chemical interaction • Bacteria • Yeast • Molds Others Microorganisms • Insects • Rodents • Animals • Birds
  • 6. Spoilage The food may become unacceptable due to the following factors: 1) Growth and activities of micro-organisms principally bacteria, yeasts and molds (This is by far the most important and common cause of food spoilage). 2) Activities of food enzymes (enzymatic browning is a common example). 3) Infestation by insects, parasites and rodents. Biological hazards
  • 7. Types of Spoilage 4) Chemical changes in a food (i.e. not catalyzed by enzymes of the tissues or of micro-organisms). For example the chemical oxidation of fats producing rancidity as well as non-enzymatic browning reactions in foods like Maillard Browning. 5) Physical changes or damages such as those caused by freezing (freezer burn), by drying (caking) etc. 6) Presence of foreign bodies. Physical hazards
  • 8. Chemical changes Chemical changes in a food (i.e. not catalyzed by enzymes of the tissues or of micro- organisms). For example the chemical oxidation of fats producing rancidity as well as non-enzymatic browning reactions in foods like Maillard Browning. Chemical reactions take place in the presence of atmospheric oxygen and sunlight. Two major chemical changes, which occur during the processing and storage of foods, are lipid oxidation and non-enzymatic browning which deteriorate sensory quality, colour and flavour .
  • 9. Chemical changes Lipid oxidation is influenced by light, oxygen, high temperature and the presence of iron and copper, and water activity. Control of these factors can significantly reduce the extent of lipid oxidation or rancidity in foods. Non-enzymatic browning is one of the major causes of deterioration which takes place during frying, cooking, storage of dried and concentrated foods through Maillard, caramelization and ascorbic acid oxidation.
  • 10. Chemical changes Maillard reaction occurs due to reactions between reducing sugars and amino acids in the presence of heat and results in formation of black brown insoluble pigments. Caramelization of sugars occurs in presence of high heat and low moisture content in the food. Oxidation of fatty acids to other chemicals like aldehydes, ketones, alcohols and esters also results in off-flavours.
  • 11. Chemical changes Maillard reaction occurs due to reactions between reducing sugars and amino acids in the presence of heat and results in formation of black brown insoluble pigments. 1912. Louis Camille Maillard a French physician and chemist
  • 12. Chemical changes Maillard reaction occurs due to reactions between reducing sugars and amino acids in the presence of heat and results in formation of black brown insoluble pigments.
  • 13. Chemical changes Maillard reaction occurs due to reactions between reducing sugars and amino acids in the presence of heat and results in formation of black brown insoluble pigments.
  • 14. Chemical changes Caramelization of sugars occurs in presence of high heat and low moisture content in the food.
  • 15. Chemical changes lipid oxidation or rancidity in foods.
  • 16. Chemical changes RANCIDITY Hydrolytic Rancidity Oxidative Rancidity Hydrolytic Rancidity Triacylglycerol Glycerol Free fatty acids (Volatile bad odour)
  • 18. Chemical changes Ascorbic acid Chemical name for vitamin C is ascorbic acid, it’s chemical formula is C6H8O6. As the name says, ascorbic acid is an acid. This means it can release protons (H+) and lower the pH of a water solution. By lowering the pH of a solution, it becomes more sour. Once ascorbic acid has given away/released its proton, the name changes to ascorbate. This reaction is reversible though, when conditions permit the proton can sit back on the ascorbate.
  • 19. Chemical changes Ascorbic acid oxidation ‘donation’ of two electrons (e–), ascorbic acid also releases two protons. This will result in a new stable molecule: dehydroascorbic acid
  • 20. Chemical changes  Hydroxylation of monophenol to o-diphenol  Dehydrogenation of o- diphenol to o-quinone ENZYMATIC BROWNING Polyphenol oxidase Phenolic substrate O2 O2 O2 O2 O2 O2 O2 Phenolic substrate Polyphenol oxidase
  • 21. Physical changes Physical changes or damages such as those caused by freezing (freezer burn), by drying (caking) etc. Freezer Burn Freezer burn is a condition that occurs when frozen food has been damaged by dehydration and oxidation, due to air reaching the food. It is generally caused by food not being securely wrapped in air-tight packaging.