Colloidal systems in food

Colloidal systems in food

1. Colloidal systems in food Presented by: Mamta sahurkar (Food technology) Laxminarayan Institute of Technology, Nagpur

2. Mixtures Is made up of two or more substances mixed together. Chemical identity of components is retained and some mixtures are easy to separate Homogenous mixtures Compositions that look same throughout Eg: Food colorings and water Heterogenous mixtures Not the same throughout Eg: oil and water Colloids Mixture consisting of particles between the size of solutions and suspensions Eg: Milk Suspensions Particles are so large that they settle out unless you stir Eg: sand and water Solutions Paticles are very small can pass through filter paper Eg: food colouring and water

3. Solutions Examples of solution are: Fruit juices Sugar and water syrups Salt and water brine A solution is formed when A liquid is dissolved in another liquid. Eg: Fruit squash in water A solid is dissolved in liquid like sugar in cup of tea Solutions will not separate when left to stand.

4. Type of Solutions Solvent Examples

5. Terminologies Solution: Homogenous mixtures of two or more substances A liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent ).Eg: Salt in water, Sugar in water. Solute T he minor component in a solution, dissolved in the solvent. Eg: Sugar in sugar solution with water Solvent A  solvent  is the component of a solution that is present in the greatest amount. It is the substance in which the solute is dissolved. Eg: Water in salt solution

6. Solubility Solute Temperature Solubility Solid Increases Increases Gas Increases Decreases Solute Pressure Solubility Solid Increases Remains same Gas Increases Increases Parameters affecting solubility Temperature Pressure Maximum amount of solute that can be dissolved in a definite amount of solvent at a specific temperature Referred to as: Ability to dissolve.

7. Nature of Solvent/Solute Like dissolves in like Solute type Non polar solvent Polar solvent Non polar(Fat/Grease) Soluble( Soap) Insoluble(water) Polar Insoluble Soluble(Water) Ionic(Salt) Insoluble Soluble High solubility implies soluble Low solubility implies insoluble

8. Types of solutions An unsaturated solution is the one in which more solute can be dissolved in a solvent at a given temperature A saturated solution is a solution containing maximum amount of solute that will dissolve at a given temperature. A supersaturated solution is a solution that contains more solute that would dissolve in a saturated solution at a given temperature. Temperature increases

9. COLLOIDS ??? All prepared  food  dishes are examples of a mixture known as a  colloid . A colloid is a type of chemical mixture where one substance is dispersed evenly throughout another. Colloids are formed when one substance is dispersed through another, but does not combine to form a solution. There are many types of colloidal systems depending on the state of the two substances mixed together .  The mixture of the two substances is called a  colloidal  dispersion or a  colloidal  system .

10. Properties of colloids A colloid is a heterogeneous mixture The size of colloidal particles is small to be seen with naked eyes The colloids are large enough to scatter beam of light passing through it and making its path visible They do not settle down if undisturbed

11. Importance of colloids in foods Provides Texture Improves mouthfeel Gives structure Stability Important for maintaining rheological properties of food systems. Eg: Whipped cream , Mayonnaise, milk , B utter ,  G elatin ,   J elly .

12. COLLOIDAL SYSTEM A colloidal system consists of two separate phases : D ispersed phase (or internal phase) C ontinuous phase (or dispersion medium). A colloidal system may be solid, liquid, or gaseous. The substance which is dispersed is known as the disperse phase and is suspended in the continuous phase. Liquid two phase system vigorously mixed During mixing During mixing

13. System Dimension One phase system Below 1 mm Colloid 1nm to 0.5 micrometer Suspensions Above 0.5 micrometer ( High affinity between dispersed phase and medium or solvent loving ) (Low affinity between dispersed phase and medium or solvent repelling) Classification based on size

14. Main types of colloidal systems

15. A  sol  is a  colloidal solution   suspension of very small   solid   particles  in a continuous  liquid   medium. Sols exhibit characteristic optical properties. They may have an opaque or clear appearance to the naked eye when viewed under a microscope, but the dispersed particles are sufficiently large to scatter and polarize the incident light to some extent. This scattering of visible light by colloidal solution is known as Tyndall effect. When viewed through an ultramicroscope, colloidal particles appear to be in a state of rapid motion called Brownian motion. SOL

16. Sol A colloid  (aggregate of very fine particles dispersed in a continuous medium) in which the particles are  solid  and the dispersion medium is fluid. If the dispersion medium is water, the colloid may be called a hydrosol; and if air, an  aerosol . Lyophobic sols are characterized by particles that are not strongly attracted to molecules of the dispersion medium and that are relatively easily coagulated and precipitated . Lyophilic sols are more stable and more closely resemble true solutions. Many sols are intermediate between lyophobic and lyophilic types .   Eg: protoplasm , gel, starch in  water , blood, paint, and pigmented ink.

17. GEL A  gel  is a solid  jelly like  material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute  cross linked  system, which exhibits no flow when in the steady-state . By weight, gels are mostly liquid, yet they behave like solids due to a three-dimensional cross-linked network within the liquid. It is the crosslinking within the fluid that gives a gel its structure (hardness) and contributes to the adhesive stick

18. Sols and Gels Sols and Gels are both liquid loving (lyophilic colloids) Sol Liquid or colloid mixture in which solid particles are dispersed in liquid phase. Dispersed phase is attracted to molecules of continuous phase. GEL . Sometimes the mixture needs to be heated and stirred. When this solution cools the sol changes into gel which resembles a solid than liquid. Both protein and starch can be used for forming gel.

19. When a jelly is made, gelatin is dispersed into a liquid and heated to form a sol.As the sol cools, protein molecules unwind forming a network that traps water and forms a gel. If cornflour is mixed with water and heated, the starch granules absorb water until they rupture ,the starch then disperses in water and the mixture becomes more viscous and forms a gel on cooling

20. S.No Sol Gel 1 The liquid state of a colloidal solution is called sol The solid or semi solid (Jelly like) stage of a colloidal solution is called gel 2 The sol does not have a definite structure Possess honeycomb like structure 3 The dispersion medium of the sol may be water or alcohol; Dispersion medium will be hydrated colloid particles 4 The sol can be converted into gel by cooling Gel can be converted into sol by heating 5 The sol can be easily dehydrated Gel cannot be dehydrated 6 The viscosity of the sol is very low Viscosity of gel is very high 7 Sol is categorized into lyophobic and lyophilic No such classification of gel 8 Example: Blood Example: Fruit jelly, cooked gelatin

21. Other types of gel are formed with pectin and agar Pectin,a form of carbohydrate found in fruits in production of jam until it is set. However ,for it to gel there must be at least 50 per cent sugar and conditions should be acidic. Agar is a polysaccharide extracted from seaweed which is capable of forming gels. If a gel is allowed to stand for a time, it starts to ‘weep’ This loss of liquid is known as syneresis . Other types of gel

22. Emulsions: A solution of one liquid with another immiscible liquid When water and oil are shaken together, they form an emulsion. If it is left to stand oil will separate at the top of water. This is an unstable emulsion.Stable emulsion is formed when two immiscible liquids are held stable by a third substance.(Emulsifying agent)

23. Food emulsions: A food emulsion is basically a two-phase system consisting of a liquid, such as oil, wax or essential oil and water. Most of the dispersed droplets in food emulsions are between 0.1 and 10 micrometers. Food emulsions Oil in water emulsions Water in oil emulsions

24. Emulsifiers Emulsifiers are the substances which reduce surface tension at the interface of two normally immiscible phases,allowing them to mix and form emulsion They belong to the general class of compounds called surface active agents Functions of emulsifiers: To promote emulsion stability Control agglomeration of fat globules Modify texture Shelf life improved Modify rheological properties Control polymorphism and improve texture of fats

25. An emulsifying agent is made up of two parts: One is hydrophilic(water loving) and other is hydrophobic(water hating). The emulsifier holds the disperse phase within the continuous phase. This results in emulsion becoming stable

26. How do they work??? Emulsifiers reduce surface tension between the two immiscible phases due to their molecular structure They have both a polar group with affinity for water and non polar group with affinity for oil

27. Mayonnaise is an example of a stable emulsion of oil and vinegar, when egg yolk(lecithin ) may be used as an emulsifying agent. Stability of emulsions Stabilizers are often added to emulsions to increase the viscosity of the product. These help to improve stability of the emulsions, as over time emulsions may separate. Stabilizers also increase shelf life,E461 methylcellulose, used in low fat spreads.

28. The particles in suspensions are larger than those found in solutions. Components of a suspension can be evenly distributed by a mechanical means, like by shaking the contents, but the components will settle out. Example: Oil and Water Suspensions

29.   Solutions Suspensions Colloids Appearance Clear, transparent and homogeneous Cloudy, heterogeneous, at least two substances visible Cloudy but uniform and homogeneous Particle Size molecule in size larger than 10,000 Angstroms 10-1000 Angstroms Effect of Light (Tyndall Effect) none -- light passes through, particles do not reflect light variable light is dispersed by colloidal particles Effect of Sedimentation none particles will eventually  settle out none

30. Foams Foam is a two phase system in which the gas(air) phase is dispersed in a small amount of liquid(water) continuous phase Foam is desirable in beer, whipped egg white,ice cream,marshmellow etc. The gas bubbles are separated from each other by liquid walls that are elastic They have large amount of entrapped gases

31. Bubbly foam A bubbly foam is formed when the amount of gas incorporated is low enough to retain roughly spherical shape Polyhedral foam The gas to liquid ratio is so large that bubbles are pressed against one another in honeycomb like structure

32. Foam formation Air has injected into the liquid Large air bubbles have broken down into smaller bubbles Smaller bubbles have to be prevented from fusing during the formation of foam

33. Foam stability Foam becomes unstable due to drainage of water from their structure. Foam stability is desirable and can be enhanced by Increasing elasticity of bubble wall Increasing viscosity of the solution Adding polar foam stabilizers

34. Antifoaming agents: In food industries undesirable foams may be formed Excessive formation leads to the loss of quality of the product especially in fermentation processes. Antifoaming agents cause the collapse of foam and retard the formation of additional foam. Eg. Silicon oils

35. Thank you