Importance of Water properties and water activity information given especially for the B.Sc and M.Sc Food Technology students.

Importance of Water properties and water activity information given especially for the B.Sc and M.Sc Food Technology students.

1. Dr.Ashwini.T Assistant Professor Food Process Engineering TDU, Bengaluru. Water Properties & Water Activity

2. Unit I Fundamentals of Food Composition & Food Chemistry - Water property and water activity

3. Introduction Water is an important constituent of all foods Present in 2 forms- Bound water Free water Bound water- part of molecule structure, not available for microbial growth, chemical and enzymatic reactions Free water- not bound to any cell components and readily available for microbial growth, chemical and enzymatic reactions 2 types of water measurement- Water content Water activity

4. Conti.. • Water: most abundant component in foods (60–95%) • Crucial for texture, stability, taste, shelf-life • Key concepts: Water properties & Water activity

5. Physical Properties of Water • Polarity – universal solvent • Hydrogen bonding – high cohesion • Density anomaly – max at 4°C • High specific heat – temperature regulation • High latent heat – important in drying & cooking

6. States of Water in Food • Free water – available for reactions & microbes • Adsorbed water – bound to macromolecules • Bound water – tightly associated, unavailable

7. • Influences texture (juiciness, crispness) • Affects stability (Maillard, lipid oxidation) • Controls microbial growth • Key in processing: drying, freezing, concentration Water in Food Systems

8. Water Activity ( a w ) – Definition • Ratio: vapor pressure of food water / pure water • Scale: 0 (dry) → 1 (pure water) • Pure water a w = 1, Dry foods a w ≈ 0

9. Importance of Water Activity • Better stability indicator than moisture • Controls microbial growth • Influences enzymatic & chemical reactions • Determines shelf-life

10. Microbial Growth v / s. Water Activity

11. Water Activity Control in Foods

12. Applications in Food Industry • Shelf-life prediction • Food safety assurance • Dry mixes & powders • Texture control in bakery, dairy, meats

13. Water activity Water activity is the measure of free water in the food product It is the water available in food for Microorganisms to grow Represented by a w The ratio of vapour pressure of food Substrate to that of pure water is called water activity(a w ) This is numerically equal to the equilibrium relative humidity (ERH) It is based on scale from 0-1 Pure water has a water activity 1.0 Most of the foods fall in a range of 0.2 to 0.99

14. Water activity of different Foods

15. WATER ACTIVITY LIMITS FOR MICRO-ORGANIMS Microorganisms Water activity Gram Negative 0.91 Gram positive 0.86 yeast 0.88 Mycotoxins 0.80 Molds 0.70 Absolute limit for all growth 0.6 The limiting value of water activity for the growth of any microorganisms is about 0.6 Below this value the spoilage of foods is not microbiological but may be due to insect damage or chemical reactions such as oxidation

16. WATER ACTIVITY IS IMPORTATNT..? Helps in determining quality and safety of foods Influences the shelf-life safety, texture, flavor and aroma of foods. Control spoilage Helps to predict which microorganism will not be potential source of spoilage Ways to control water activity- 1. removal of free water 2. adding sugar or salt

17. Summary • Water affects food quality, texture, processing • Water activity (aₚ) determines stability • Controlling aₚ is key for preservation & safety

18. References • Fennema, O.R. Food Chemistry • Fellows, P. Food Processing Technology • Journal articles on water activity in foods

19. Thank you