Prerequisite: 

Importances of Water in Food

Structure of Water

Forms of Water in Food

Physical Properties of Water

Chemical Properties of Water

Moisture determination in Food

Water activity of Food

pH & Buffers

Water is a fundamental component in both food and biological systems, playing crucial roles due to its unique properties. Its presence and behavior are essential for chemical reactions, nutrient transport, structural stability, and metabolic processes in all living organisms.

Properties of Water

1. Polarity: Water is a polar molecule, with oxygen being slightly negative and hydrogen slightly positive. This polarity allows it to form hydrogen bonds with other molecules, making it an excellent solvent.

2. High Specific Heat Capacity: Water can absorb a significant amount of heat before its temperature rises. This property stabilizes temperatures in biological systems and food during heating and cooling processes.

3. High Heat of Vaporization: It takes a considerable amount of energy for water to evaporate. This property is essential for cooling mechanisms in biological systems, such as sweating, and in food processing, like drying and steaming.

4. Cohesion and Adhesion: Water molecules stick to each other (cohesion) and to other surfaces (adhesion). These properties contribute to capillary action, which is essential for nutrient and water transport in plants.

5. Density Anomaly: Water is denser in its liquid state than in its solid state. This is why ice floats, creating an insulating layer on bodies of water that supports aquatic life during freezing temperatures.

Importance of Water in Biological Systems

1. Solvent for Biochemical Reactions: Water is the solvent in which almost all biological reactions occur. It dissolves nutrients, gases, and wastes, facilitating cellular functions.

2. Nutrient and Waste Transport: Blood, which is primarily water, carries nutrients and oxygen to cells and removes waste products.

3. Temperature Regulation: Water helps regulate temperature in organisms, absorbing heat with minimal temperature change and cooling organisms through evaporation (e.g., sweating).

4. Cell Structure and Stability: Water contributes to cell turgor (firmness) in plants, maintaining structure and rigidity, and in animals, it provides cells with a balanced environment for protein stability.

Importance of Water in Food Systems

1. Solvent and Medium for Reactions: Water dissolves salts, sugars, and proteins in food, enabling enzymatic and chemical reactions during cooking and digestion.

2. Texture and Palatability: The water content of food affects its texture and mouthfeel. For instance, water gives fruits and vegetables crispness and affects the juiciness of meats.

3. Heat Transfer: Water efficiently transfers heat during cooking methods like boiling, steaming, and braising, ensuring even cooking and texture changes.

4. Food Preservation: Controlling water activity (the availability of water for microbial growth) is crucial for food preservation. Dehydration, freezing, and adding salts or sugars reduce water activity, extending shelf life.

5. Fermentation: Water is essential for microbial activity in fermentation processes, such as in bread-making, yogurt, and alcoholic beverages.

Water Activity in Food Systems

• Water Activity: This refers to the amount of free water available for microbial growth and chemical reactions. High water activity promotes bacterial growth, while low water activity (as in dried or salted foods) inhibits it, aiding in food preservation.

In summary, water's unique properties make it indispensable for biological stability, nutrient transport, cellular reactions, and food structure. Its behavior and availability influence everything from metabolic processes in cells to the taste, texture, and preservation of food.