(Food Science)
Physical & Physiological Changes in Food
(Colloidal Chemistry, Enzymes & Protein Denaturation)
Prepared For:
Food Science & Nutrition / Dietetics / Food Technology
Students
Prepared By:
Alina Siddiqui
Includes Topics:
✔ Colloidal Chemistry – Emulsions, Foams, Sols, Gels
✔ Osmotic Pressure in Foods
✔ Enzymatic Browning & Enzymes in Food Processing
✔ Protein Denaturation
✔ Short Questions | Long Questions | MCQs with Answers
This study material is designed to help students understand
concepts in a simple, clear and exam-oriented manner with
real-life food examples.
1
,Physical & Physiological Changes in Food
Food undergoes a variety of changes during processing, storage, cooking, transportation, and
preservation. These changes affect the appearance, texture, flavor, nutritive value, safety, and
shelf-life of food. Understanding these transformations is essential in food science, nutrition, food
technology, and food service management, as it helps maintain quality and improve consumer
acceptability.
1. Physical Changes in Food
Physical changes are changes in the form, structure, or state of food without altering its chemical
composition. These changes mainly affect texture, shape, appearance, and consistency, but the
original nutrients remain the same.
Key Types of Physical Changes
a) Phase Changes (State Changes)
Food can change its physical state during processing:
• Freezing – Water converts to ice; reduces microbial growth and increases shelf life.
• Melting & Thawing – Ice melts to water; may cause drip loss in meat & fish.
• Evaporation & Drying – Removal of water results in concentrated texture.
• Condensation – Water vapor turns to liquid during storage, may cause spoilage.
Example:
Milk freezes into ice cream, bread loses moisture and becomes stale, vegetables lose firmness when
frozen badly.
b) Changes in Texture
Processing techniques such as cutting, grinding, heating, and cooling affect texture:
• Softening of vegetables during cooking
• Tenderization of meat
• Swelling of cereals and pulses during soaking & cooking
• Gel formation in jelly and custard
• Firming during refrigeration
Texture change influences mouthfeel, palatability, and consumer acceptance.
2
, c) Colloidal Changes in Food
Many foods exist as colloidal systems, meaning particles are dispersed in another substance without
dissolving completely.
Common Food Colloids
• Emulsions – Milk, mayonnaise, salad dressing
• Foams – Cream, cake batter, beaten egg white
• Sols – Soups, sauces, gravies
• Gels – Jelly, custard, cheese, curd
These affect stability, thickness, smoothness, and structure of foods.
d) Osmotic Changes
Due to osmosis, water moves from lower solute concentration to higher solute concentration.
Examples:
• Salting pickles → Water comes out of vegetables
• Sugar in jams → Prevents microbial growth
• Rehydration of dried foods → Water moves back inside food tissue
This is very important in preservation techniques.
e) Mechanical Changes
These occur during handling and processing:
• Cutting, slicing, peeling
• Grinding wheat into flour
• Churning milk into butter
• Mixing & kneading dough
These do not change chemical nature but modify usability and appearance.
2. Physiological (Biochemical) Changes in Food
Physiological or biochemical changes occur due to enzymatic reactions or metabolic activities within
food. These changes may affect nutritional value, color, taste, aroma, and shelf life.
Such changes commonly occur in:
• Fresh fruits & vegetables
3
Physical & Physiological Changes in Food
(Colloidal Chemistry, Enzymes & Protein Denaturation)
Prepared For:
Food Science & Nutrition / Dietetics / Food Technology
Students
Prepared By:
Alina Siddiqui
Includes Topics:
✔ Colloidal Chemistry – Emulsions, Foams, Sols, Gels
✔ Osmotic Pressure in Foods
✔ Enzymatic Browning & Enzymes in Food Processing
✔ Protein Denaturation
✔ Short Questions | Long Questions | MCQs with Answers
This study material is designed to help students understand
concepts in a simple, clear and exam-oriented manner with
real-life food examples.
1
,Physical & Physiological Changes in Food
Food undergoes a variety of changes during processing, storage, cooking, transportation, and
preservation. These changes affect the appearance, texture, flavor, nutritive value, safety, and
shelf-life of food. Understanding these transformations is essential in food science, nutrition, food
technology, and food service management, as it helps maintain quality and improve consumer
acceptability.
1. Physical Changes in Food
Physical changes are changes in the form, structure, or state of food without altering its chemical
composition. These changes mainly affect texture, shape, appearance, and consistency, but the
original nutrients remain the same.
Key Types of Physical Changes
a) Phase Changes (State Changes)
Food can change its physical state during processing:
• Freezing – Water converts to ice; reduces microbial growth and increases shelf life.
• Melting & Thawing – Ice melts to water; may cause drip loss in meat & fish.
• Evaporation & Drying – Removal of water results in concentrated texture.
• Condensation – Water vapor turns to liquid during storage, may cause spoilage.
Example:
Milk freezes into ice cream, bread loses moisture and becomes stale, vegetables lose firmness when
frozen badly.
b) Changes in Texture
Processing techniques such as cutting, grinding, heating, and cooling affect texture:
• Softening of vegetables during cooking
• Tenderization of meat
• Swelling of cereals and pulses during soaking & cooking
• Gel formation in jelly and custard
• Firming during refrigeration
Texture change influences mouthfeel, palatability, and consumer acceptance.
2
, c) Colloidal Changes in Food
Many foods exist as colloidal systems, meaning particles are dispersed in another substance without
dissolving completely.
Common Food Colloids
• Emulsions – Milk, mayonnaise, salad dressing
• Foams – Cream, cake batter, beaten egg white
• Sols – Soups, sauces, gravies
• Gels – Jelly, custard, cheese, curd
These affect stability, thickness, smoothness, and structure of foods.
d) Osmotic Changes
Due to osmosis, water moves from lower solute concentration to higher solute concentration.
Examples:
• Salting pickles → Water comes out of vegetables
• Sugar in jams → Prevents microbial growth
• Rehydration of dried foods → Water moves back inside food tissue
This is very important in preservation techniques.
e) Mechanical Changes
These occur during handling and processing:
• Cutting, slicing, peeling
• Grinding wheat into flour
• Churning milk into butter
• Mixing & kneading dough
These do not change chemical nature but modify usability and appearance.
2. Physiological (Biochemical) Changes in Food
Physiological or biochemical changes occur due to enzymatic reactions or metabolic activities within
food. These changes may affect nutritional value, color, taste, aroma, and shelf life.
Such changes commonly occur in:
• Fresh fruits & vegetables
3
