Introduction to Food Emulsions and Foams

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FOOD COLLOIDS: EMULSIONS &

FOAMS Prepared & Presented by:

Professor Abd Karim Alias Universiti Sains Malaysia

Abd Karim Alias, 2013 1

Photo courtesy of Jangray1985, Flickr

Photo courtesy of Danny Ngan, Flickr

Emulsion & Foam by Prof. Abd Karim Alias is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

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} Define these terms: disperse systems, colloids, emulsion, foam, amphiphilic, lipophilic, hydrophilic, emulsifier, stabilizer, surface tension, interfacial tension, plateau border.

}  Identify types of emulsion & foam

} Describe methods to form an emulsion & foam

} Explain why energy is necessary to form an emulsion

After completing this topic, you should be able to do the followings:


} Explain why an emulsion is inherently unstable } Explain the role of emulsifier and stabilizer

} Decribe the DLVO theory } Describe the various ways by which emulsion

and foam become unstable

} Explain the method to measure and predict emulsion stability

} Describe methods to stabilize emulsion and foam

After completing this topic, you should be able to do the followings:


} Food Emulsions: Principles, Practice, and Techniques --D.J. McClements, CRC Press, Washington DC, 1999

} Emulsifiers -- C.E. Stauffer, Eagan Press, St. Paul, Minnesota, USA, 1999

} Analysis of Food Emulsions -- Chapter 35 in Food Analysis, 2nd edition (S.S. Nielsen, ed.)

References

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What do mayonnaise, margarine, butter, milk and coconut milk have in common?

–Ans: Emulsion

What do ice cream, meringue, marshmallow, bread, and cake batter have in common?

– Ans: Foam

Emulsion & Foam are dispersed system

Questions:

Abd Karim Alias, 2013

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÷ The term Dispersed System refers to a system in which one substance (the dispersed phase) is distributed, in discrete units, throughout a second substance (the continuous hhase)

÷ Each phase can exist in solid, liquid, or gaseous state

DISPERSED SYSTEM (DISPERSION)

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• COLLOIDAL DISPERSION (SOL) – dispersions of two or more immiscible materials, containing structural entities in the size range 1 nm – 1 µm.

• The simplest type of colloidal system consists of a single dispersed phase of particles in a second continuous phase called dispersion medium.

TERMINOLOGY

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Dispersed phase

Continuous phase

Interface


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SOLID LIQUID GAS

SOLID Some glasses

Sol Smoke

LIQUID Emulsion Aerosol

GAS Solid foam

Foam

CONTINUOUS PHASE

DIS

PERS

ED P

HA

SE

TYPES OF DISPERSED SYSTEM


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• A system containing particles >1 mm which are prone to settle under gravity is usually referred to as a suspension.

• A dispersion or suspension of liquid droplets in a liquid continuous phase is called an emulsion.

• A foam is a coarse dispersion of gas bubbles in a liquid (or solid) continuous phase

TERMINOLOGY


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Diameter /µm0.1 1 10

Freq

uenc

y /%

0

5

10

15

20

25

30

35

Emulsion 1

Emulsion 3

Emulsion 5

Fig. 1

Polydispersity

• Monodisperse

• Polydisperse


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Volume Fraction φ=Total volume of the dispersed phase ÷ Total volume of the system

Close packing, fmax Monodisperse

Ideal ~0.6 Random ~0.5

Polydisperse

Much greater


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• In food systems, the term “colloids” generally includes dispersions containing larger particles (> 1 mm).

• Food dispersions encompass suspensions such as sugar fondant (solid sugar particles in a saturated sugar solution), emulsions such as milk, cream, and spread, and foams such as found in beer, ice cream and bread.

FOOD COLLOIDS


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Foam

Oil phase (containing flavours, fat

solublenutrients Fat crystals

Sugar crystals

Aqueous phase (containing flavours, water soluble

nutrients, salts, stabilisers

Emulsifier layer around

droplet

Macromolecule

Macromolecule adsorbed on droplet

surface


Introduction to Food Emulsions and Foams

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