Chapter 20 – Solutions and Colloidal Dispersions

1. Chapter 20 – Solutions and Colloidal Dispersions Mrs. Wagner – Food Science

2. Solutions • Mixtures of at least two substances – a solute dissolved in a solvent. • Solutes can be: • Solids – salt, sugar, vitamin C • Liquids – acetic acid in vinegar • Gases – carbon dioxide found in carbonated beverages • The solvent is always a liquid, usually water.

3. Solutions • Food Scientists study how solutions function – they study the reactions in the body. • Ex. Glucose and water-soluble vitamins ate in solution when they are carried in the blood. • After studying such solutions as fruit juice, coffee, tea, etc. nutritionists and food scientists gather new information, create new methods of production and preservation, and pass along nutrition advice to people.

4. Solutions • Unsaturated – As long as a solution contains less solute than can be dissolved in it at a given temperature. • Saturated – A solution that contains all the solute that can be dissolved at a given temperature. • A point is eventually reached when no more solute will dissolve. • Figure 20-1 Page 311 in your text

5. Solubility • The temperature of a solution affects solubility. • Can of Soda – How fast will it become flat? • At what temperature?? • Cold? • Room Temperature? • Warmed up?? • WARMED UP – Gases escape more quickly at a higher temperature!!

6. Solubility • The solubility of most solids dissolve in a liquid increases as the temperature rises. • Instant Iced Tea Example • Supersaturated Solution – is one that contains more dissolved solute than it would normally have at that temperature before it was heated.

7. Solutes and Phase Changes • The amount of solute in a solution affects the temperature at which the solution boils or freezes. • When a solid is dissolved in a liquid, the solution boils at higher temperature and freezes at a lower temperature than the pure solvent does. • The more solute present in a solution, the higher the boiling point and the lower the freezing point.

8. Vitamins and Minerals in Solutions • Water-soluble vitamins and minerals are lost through the cooking process. • Depends on two factors: • Surface Area: a thinly sliced potato will lose more nutrients than a densely cut piece. • Cooking Time: Length of…longer cooking time, more nutrients are lost • Where are all of the vitamins and minerals??

9. Vitamins and Minerals in Solutions • In the water!! • Use it or lose it… • Use it in mashed potatoes or soup!

10. Colloidal Dispersions • The particles of one substance is distributed or dispersed in another substance without dissolving. • Much like a solution, however, different mainly due to particle size.

11. Phases in Colloidal Dispersions • Phases in Colloidal Dispersions • Solid • Solid in liquid – Gravy • Liquid in solid – Baked Custard • Liquid • Italian Salad Dressing is a liquid dispersed in another liquid – vinegar and oil • Gas • Beaten egg whites, gas is dispersed in a liquid

12. Phases in Colloidal Dispersions • The substance that is dispersed within another is called the dispersed phase. • The substance that extends throughout the system and surrounds the dispersed phase is called the continuous phase.

13. Properties of Colloidal Systems • Particle Dispersion – Under stable conditions, particles in a colloidal dispersion will not settle on the bottom – they remain suspended in the liquid. • Ex. Calcium and Magnesium Phosphates that are colloidally dispersed in milk.

14. Properties of Colloidal Systems • Tyndall Effect – When a light beam passes through a colloidal dispersion, you can see the path of light. The dispersed particles are large enough to scatter, or deflect, visible light. • Figure 20-3 Page 314 in your text

15. Properties of Colloidal Systems • Concentration – The concentration of solids in a colloidal dispersion has almost no effect on boiling or freezing point. • Stability – The curdling of milk is due to the instability of the protein casein.

16. Colloidal Dispersions • Two Main Types • Emulsions • Foams

17. Emulsions • Mixture of two liquids that do not normally blend. • Because they cannot combine naturally they are said to be immiscible. • Two basic emulsions • Oil-in-water • Water-in-oil • Tiny droplets = oil-in-water emulsion

18. Emulsions • Emulsions found in the food industry: Milk – Cream – Ice Cream – Butter – Processed Cheese – Mayo • All are opaque because the particles are large enough to deflect light rays from their normal path.

19. Temporary Emulsions • Vinegar-and-oil salad dressing • Shaking or stirring will mix them, but only for a short time…then the oil is floating on the vinegar. • Reason – Each has molecules that attract like molecules and repel dissimilar molecules.

20. Permanent Emulsions • Adding an emulsifier to a mixture can keep one liquid permanently dispersed in the other. • The molecules of an emulsifier usually have a polar end that dissolves well in water and a non-polar end that dissolves in fat. • The emulsifier holds the emulsion together.

21. Emulsifiers in Foods • Egg yolk – Mayo • Starch – Gravy/Sauces • If gravy starts to separate, add water so that the polar end has something to grab onto.

22. Emulsifiers in Foods • Common Food Emulsions • Milk – Homogenization – prevents the fat (cream) from separating • Mayonnaise – oil-in-water • Butter – water-in-oil – agitating cream – 80% butterfat by weight

23. Food Foams • Whipped Cream – Air is beaten into the cream, while protein in the cream serves as an emulsifier. • The more viscous a liquid is, the better the foam – that is why cream creates a better foam than milk!

24. Food Separation Techniques • Knowing how to separate the solvent from the solute in solutions allows food scientists to produce the powdered products that consumers can re-dissolve to make instant fruit drinks, iced tea, etc. • Usually done through evaporation • Distillation is also used – method where evaporation of a liquid occurs and then condense the vapors.

25. Food Separation Techniques • Filtration – Pouring a liquid through a porous material such as filter papers to catch solid particles • Drip Coffee Makers • Osmosis – Movement of a fluid through a semi-permeable membrane • Salt on eggplant to draw out fluid/water – a.k.a sweating the eggplant