Food Analysis Previous Exam III

University of Kentucky, Department of Animal & Food Sciences, FSC 535

1. True (T) or False (F) (20 pts.)

The dehydroascorbic acid content of a sample cannot be assayed with 2,6-dichloroindophenol.

Loss of phytol from chlorophyll makes the color change from green to olive-brown.

Xanthophylls are more polar than carotenes.

Myoglobins must be extracted prior to their analysis.

Kjeldahl assay measures only protein nitrogen.

The Biuret method quantifies only soluble proteins.

In SDS PAGE electrophoresis, separations are based on the charge of individual proteins.

Denatured proteins are generally less soluble in water than their native counterpart.

The Bradford Dye-Binding method of quantifying proteins uses a fluorescent indicator.

Cis-parinaric acid binds to the negatively charged regions of proteins.

 2. What is the difference in the assays that allows the SDS binding assay to measure total protein surface hydrophobicity and limits the use of fluorescent probes to measure only the surface hydrophobicity of soluble proteins? (6 pts.)

3. For calculating the protein content by the Kjeldahl method, the following equation is used:


5 mLs HCL x 0.1 N HCl x 14 x 6.25 x 100           =       43.75% protein

1000 x 0.1 gram sample

Describe the terms in bold type and the significance of these values. (6 pts.)

4. Describe three (3) mechanisms for the separations of proteins (not involving precipitation) and give an example of an analytical technique using each mechanism. (9 pts.)

5. Explain why (or why not) a colorimetric assay for vitamin A activity would (or would not) be accurate. (6 pts.)

6. Explain the mechanism that cause proteins to precipitate during Isoelectric precipitation and the mechanism that causes precipitation with ammonium sulfate. (4 pts.)

7. Describe the spectrophotometric assay of anthocyanins. (510-540 nm). (5 pts.)

8. What is a potential problem with the precipitation of protein with ethanol? (3 pts.)

9. Briefly describe how reflectance spectrometer works and some of its uses. (6 pts.)

10. List three vitamins that can be separated by HPLC and detected with a fluorometer (either in their native states or as derivatives). What is the advantage of a fluorometer over a dioade array detector? (6 pts.)

11. Briefly write down the differences between the following items. (14 pts.)

a. Dialysis vs. Ultrafiltration

b. Metmyoglobin vs. Oxymyoglobin

c. Bioassy vs. Physiochemical vitamin assay.

d. Kjeldahl vs MacroN Analyzer

e. Biuret vs. Lowry Method of Quantifying Protein

f. Chlorophyll vs. Pheophytin

g. Vitamin A vs. Carotenes

12. While your are working as the director of quality assurance for a major food company, your "Cheeze-Whiz" product has experienced a loss in viscosity compared to the product specifications. You suspect the whey protein (a major ingredient) is the blame. You are not sure if your supplier has substituted a cheaper protein source into his product or if the protein has somehow been improperly processed (e.g., exposure to high heat). Describe the analysis your would order to answer these question about the quality of the whey protein isolate and what you would hope to learn from each assay. (15 pts.)