Water in Food: Water is one of the most important constituents of food, as it affects texture, nutrient solubility, and preservation.

Moisture Content in Fruits and Vegetables:

• Fruits and Vegetables: Most fruits and vegetables contain 70-80% moisture. However, certain vegetables like leafy greens and melons may have up to 92-95% water content.
  • Examples:
    • Cucumber, lettuce, melons: 95% moisture
    • Many fruits and vegetables: >80% moisture
  • Starchy Vegetables: Tubers such as cassava, yam, and corn are starchy and contain less moisture (around 50%). These have a higher dry matter content compared to fresh fruits and vegetables.

Role of Moisture:

• Nutrient Solubility: Many nutrients in fruits and vegetables are soluble in water, making moisture essential for maintaining the nutrient profile.
• Perishability: Moisture acts as a medium for microbial growth, and foods high in moisture are more prone to spoilage. This is why fruits and vegetables tend to spoil quickly when exposed to air.
• Shelf Life Considerations: Retaining moisture or preventing its loss is crucial for extending the shelf life of produce. Harvesting at the time when the maximum water content is present can also ensure the produce is fresh and crisp.

Water Content Variation During Harvest:

• Temperature Influence: The water content of produce can fluctuate depending on environmental factors such as temperature and humidity at the time of harvest. This is why it’s ideal to harvest produce during cooler times of the day, as they are likely to have higher moisture content, which results in better texture and longer shelf life.
• Crisp Texture: Fruits and vegetables harvested with higher moisture content tend to be crisper, a quality highly valued in fresh produce.

Examples of Moisture Content in Foods:

• Fruits: 79-90% moisture
• Vegetables: 70-90% moisture
• Milk: 87% moisture
• Bread: 35% moisture
• Honey: 20% moisture
• Butter: 16-18% moisture
• Milk Powder: 4% moisture
• Edible Oil: 0% moisture

Water in Food Preservation:

Chemical and Physical Reactions: Water in food is involved in numerous chemical and physical processes that influence the quality and shelf life. For example:

• Removal of Water: Physical (drying) or chemical (binding with sugar or salt) methods to reduce water content can inhibit microbial growth and slow down enzymatic reactions, thus prolonging the food’s shelf life.
• Interaction with Food Macromolecules: Water interacts with proteins, carbohydrates, and fats, contributing to the texture and consistency of food. For instance, water binds to starch molecules in bread dough, affecting the dough’s elasticity and final texture.

Water Activity (aw) in Food:

Water activity (aw) is a crucial concept in food science and refers to the free or unbound water in a food product, which is available for microbial growth and chemical reactions. It is different from moisture content, which represents the total water present in the food.

• Definition of Water Activity (aw): Water activity is defined as the ratio of the vapor pressure of water in the food to the vapor pressure of pure water at the same temperature.Water activity values range from 0 (completely dry) to 1.0 (pure water). The higher the water activity, the more likely it is for microorganisms to grow.
• Importance of Water Activity: Microbial Growth: High water activity (close to 1.0) supports the growth of bacteria, yeasts, and molds, which can spoil food.Shelf Life: Reducing the water activity of a food product can significantly improve its storage stability. This is why many foods are dried or preserved with substances that bind water (e.g., salt, sugar, or humectants).
• Impact on Food Storage:Optimal Water Activity for Preservation: Food with a water activity between 0.2 and 0.4 is highly stable. This range reduces microbial spoilage and prevents non-enzymatic browning and lipid oxidation. Intermediate Moisture Foods: Foods with an aw between 0.6 and 0.9 are called “intermediate moisture foods” (e.g., dried fruits, jams). These foods require additional protection from microbial contamination to extend their shelf life.

Examples of Water Activity in Different Foods:

1. • Fresh Meat and Fish: 0.99 (high water activity, prone to microbial spoilage)
   • Bread: 0.95
   • Aged Cheese: 0.85
   • Jams and Jellies: 0.8
   • Dried Fruits: 0.6
   • Milk Powder: 0.2
   • Instant Coffee: 0.2 (very low water activity, highly stable)

By controlling water activity, food manufacturers can control spoilage, prevent microbial growth, and enhance the storage life of products.

Functions of Water in the Body:

Water plays several essential roles in maintaining bodily functions:

1. Building Material: Water is a key component of every cell in the body, making up a significant portion of their structure.
2. Universal Solvent: Water dissolves nutrients, allowing them to be transported throughout the body. It dissolves waste products, allowing the body to excrete them through processes like urination.
3. Regulation of Body Fluids:
   • Blood: Contains about 90% water and helps transport gases (like oxygen and carbon dioxide), nutrients, and waste products to and from cells.
   • Urine: Contains about 97% water and helps excrete waste material, including metabolic byproducts like urea and excess salts.
4. Chemical Reactions: Water is involved in many chemical reactions in the body, including the breakdown of sugars and fats. It is a crucial reactant in metabolism.
5. Lubrication: Water acts as a lubricant in joints, reducing friction and preventing damage to tissues.
6. Temperature Regulation: Water regulates body temperature through the process of evaporation. Sweat, which is mostly water, helps cool the body when it becomes overheated.

Sources of Water for the Body:

1. Direct Water Intake: The primary source of water for the body is drinking water.
2. Beverages and Liquid Foods: All liquids, such as soups, beverages (tea, juice), and milk, contribute to hydration.
3. Metabolic Water: The body also generates water through metabolic reactions like the breakdown of carbohydrates, fats, and proteins. This provides an additional source of water.

Health Problems Related to Water:

Dehydration: Dehydration occurs when there is insufficient water intake or excessive loss due to factors like vomiting, diarrhea, or sweating. Consequences of Dehydration: If untreated, dehydration can cause severe health issues, including kidney damage, heatstroke, and death. Symptoms include dizziness, dry mouth, and reduced urine output. Infants at Risk: Due to their higher body water content, infants are at greater risk of dehydration, especially during illnesses like diarrhea. Oral rehydration solutions, coconut water, or lemon-based drinks are essential for rehydration.

Edema: Definition: Edema is the abnormal accumulation of fluid in tissues, often caused by the body’s inability to excrete sodium effectively, leading to water retention. Causes: Kidney failure, heart disease, or excessive sodium intake can cause edema, leading to symptoms like swelling, especially in the legs, ankles, and abdomen. Excessive Water Loss: Excessive loss of water can occur due to prolonged sweating (in hot weather or strenuous physical activity), vomiting, or diarrhea. In these cases, it’s essential to replenish fluids promptly to avoid complications.