Functional Properties of Proteins - Foams

FST 605 - Laboratory


Date Performed: January 19,1999

Report Due: January 26, 1999

The ability of a protein suspension to form a stable foam is dependent upon its physical form, the pH of the suspension and on the presence of other constituents. The following lab will examine some of the variables that are important in obtaining a stable foam with acceptable overrun.


The instructor will assign to you one of the following protein sources:

  • 1. Calcium Caseinate

    2. Whey 1

    3. Soy Isolate

    4. Egg

    5. Whey (2)

    •


    Methods

    General Procedure for Determining Foam Stability and Percent Overrun

    Place 1. 5 g of protein in 50 ml of water, buffer or salt solution and blend for one minute at the highest speed of the blender. Pour the foam into a graduated cylinder (l00 ml for whey protein, 250 ml for caseinate and soy) . Determine:

    a) Percent overrun = percent increase in volume of the material:

    Overrun = (total volume - 50 ml) X 100
 	__________________________________
			50 ml


    b) Foam stability = % overrun after 5 minutes

    Variables

    I. pH. Measure the foaming of protein suspensions as described above. Add 1.5 g protein to 50 ml of 0.67M phosphate buffer adjusted to pH 5, 6, 7, 8 and .2M glycine/NaOH adjusted to pH 9.0. Which pH gave the highest overrun at 10 minutes?

    II. Sugar. Select the pH that gave the best overrun at 10 minutes and prepare samples with 0, 5, and 10% sugar added. Which sample gave the greatest overrun at 10 minutes?

    III. Salt To the above sample with the greatest overrun at 10 minutes, add 0, 1.5 or 2.0 % NaCl and evaluate. Which sample gave the highest overrun at 10 minutes?

    IV. Fat. To the above sample selected as giving the highest overrun at 10 minutes add 0., 0.5 or 1.0% fat and evaluate. Which sample gave the greatest overrun at 10 minutes?


    What combination of pH, sugar, salt, and fat gave the best overrun at 10 minutes for the protein sample assigned to you? The instructor will provide you with data obtained by the rest of the group for the remaining protein sources.


    Results:

    For your protein source construct the following plots:

    1. pH vs overrun at 10 minutes

    2. Sugar vs overrun at 10 minutes

    3. Salt vs overrun at 10 minutes

    4. Fat vs overrun at 10 minutes


    Construct a table containing all the data from all of the groups .

    Discussion:

    What conditions provided the best combination of overrun and stability for each of the proteins tested? Discuss how each factor varied affects both overrun and foam stability.


    Questions

    1. What types of food products might contain foams of this type?

    2. What proteins are now utilized in these food products?

    3. How does a protein suspension incorporate air?

    4. From what you know about the structure of the protein utilized, explain why some proteins performed better than than others under any set of conditions you select .

    5. Some literature reports suggest that mild heat treatment of whey proteins improves their ability to form stable foams. How might this work?