1. The effect of heat treatment on the protein denaturation and functional prope
ID: 282200 • Letter: 1
Question
1. The effect of heat treatment on the protein denaturation and functional properties of egg yolks was determined.The egg yolk consists of 2 phases: the plasma (aqueous phase) and granules (insoluble particles).In Fig. 4, the emulsion is most stable when the median diameter of the droplets are small.Refer to the following figures to answer the following questions.Support your answers with a discussion of the food chemistry concepts.
a. Estimate the temperature at which denaturation of the egg yolk protein occurs. Indicate the results in the above figures which support the denaturation temperature you determined.
b. Discuss the effects of the heat treatment on the 1°, 2°, and 3° structure of the proteins. Indicate the bonds that are altered by the processing treatment.
c. To ensure the microbial safety of the egg yolk, the company you are working for would like to heat the egg yolks to 75C before using as an emulsifier in mayonnaise. Would you support this decision? Based on the results in the figures, discuss the effect of heat on the functionality of egg yolk as an emulsifier.
d. Discuss the properties of a protein that are important for a protein to function as an emulsifier. Discuss how these properties change as a result of heat treatment and the effect of these changes on the effectiveness of the egg yolk proteins to function as an emulsifier.
granes 75 Temperature (C) Fig. 1-Changes in apparent viscosity of yolk, plasma and granules as related to temperature. 24.0:0.5 % dry matter ; viscosity mea- surement: shear rate-40 s at 25 C.Explanation / Answer
1) The denaturation of the egg yolk occurs between the temperatures of 70-75 degree celsius based on the graphs which shows a sharp increase in viscosity and a sharp decrease in solubility at the above mentioned range, also since tthe emulsiuon of yolk is most stable when the median diameter of the granules is small we can see that 70-75 degrees is aloso when the diameter of the granules increase sharply.
2) In terms of denaturation the tertiary structure oor the native functional structure will undegro un folding and form into its primary structure. Egg yolk contains the proteins lipoproteins, livetins and phosvitins. Various hydrogen bonds in the scondary structure are dispersed and a crosslinking and matrix formation occure giving egg yolk its characteristic texture.
3) The heating option would lower the yolk's value as an emulsifier. In various tudies it has ben shown that untreated plasma and granules function better as an emulsifier than heat treated plasma and granules
4) the emulsification properties of proteins depend on its ability to form around the granules adsorbtion spheres, and its ability to lower surface tension on the oil water interface. ALL this depends on the protein in yolk maintaining its Trtiary structure which is lost with the heat treatment.
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