1. Intro to Physical Chemistry in Foods

It is the branch of food science that studies how physical and chemical principles explain the structure, behavior, and stability of food systems.

physical chemistry of foods

Importance of physical chemistry in food science

• provides the foundation for understanding food behavior at molecular and macroscopic levels

• links chemical composition with physical properties to guide food design, processing, and storage

Give practical examples of how physical chemistry applies in food science.

• explains ice cream graininess after repeated freezing and thawing (ice crystal growth)

• predicts sugar concentration needed to prevent crystallization in candies

• explains mayonnaise stability as an emulsion

• guides shelf-life prediction using reaction kinetics

How does physical chemistry explain food structure and properties?

By describing intermolecular forces (hydrogen bonding, van der Waals, ionic forces) that determine texture, solubility, and stability.

• Example: mayonnaise stability due to lecithin.

How is physical chemistry applied in food processing and preservation?

It explains phase changes (freezing, drying, evaporation) through thermodynamics and heat transfer, helping optimize freeze-drying, pasteurization, and baking.

How does physical chemistry relate to texture and sensory quality?

It links colloidal science with mouthfeel and explains crystallization phenomena in chocolate (tempering), ice cream (ice crystals), and sugar syrups (supersaturation control).

How does physical chemistry help in shelf-life and stability?

It predicts chemical changes (Maillard browning, oxidation) and physical changes (phase separation, sedimentation), guiding the use of stabilizers, emulsifiers, and packaging.

How does physical chemistry support product innovation?

By enabling controlled modification of viscosity, gel strength, and aeration, allowing the creation of novel products like plant-based dairy alternatives or low-fat creamy foods.

What role does physical chemistry play in safety and quality control?

It provides analytical techniques such as spectroscopy, chromatography, and calorimetry to ensure product consistency, safety, and compliance with regulations.

What are the three states of water?

• free

• bound

• immobilized

This water behaves like pure water and supports microbial growth.

free water

This water is tightly bound to molecules, unavailable to microbes, and doesn’t freeze easily.

bound water

This water is trapped in structures like gels and is partly available.

immobilized water

It is the ratio of vapor pressure of water in food to that of pure water at the same temperature.

water activity

How does freezing affect food quality?

It reduces microbial activity but large ice crystals damage texture, causing graininess.

A change in amorphous solids (like sugars) from brittle to rubbery; important for storage stability in dried foods.

glass transition

What is the glass transition in foods?

A change in amorphous solids (like sugars) from brittle to rubbery.

What does the First Law of Thermodynamics state and how does it apply to food?

Energy is conserved; in cooking, heat transfer changes temperature or phase but energy is not lost.

What does the Second Law of Thermodynamics imply for foods?

Systems move toward disorder (entropy), explaining why foods degrade over time.

What does Gibbs Free Energy (ΔG) tell us about food processes?

• ΔG < 0 → process is spontaneous.

• Example: Chocolate fat bloom occurs when unstable polymorphic fat crystals rearrange.

What are the main types of dispersed systems in foods?

• solutions

• colloids

• suspensoids

How are dispersed systems stabilized?

• Emulsifiers reduce surface tension, preventing coalescence.

• Thickeners increase viscosity, slowing separation.

It is the formation of a protein gel network, e.g., yogurt, tofu, gelatin desserts.

gelation

Why is glass transition important in dried foods?

It determines stickiness, caking, and overall storage stability.

What factors affect reaction rates in foods?

• temperature

• concentration

• catalysts

It predicts how reaction rates change with temperature → useful for shelf-life testing.

Arrhenius Equation

How does surface tension affect foods

Influences foaming (whipped cream, meringues) and emulsification (mayonnaise).

It controls flavor retention and release, and interactions with packaging.

adsorption

What are the three modes of heat transfer in foods?

• Conduction – heat transfer in solids (baking bread).

• Convection – fluid heat transfer (soups, frying).

• Radiation – energy transfer via waves (grilling, microwaving).

Give examples of mass transfer in foods.

• Salt diffusion during meat curing.

• Water migration in baked goods, leading to staling.