Food Chemistry Previous Exam III

University of Kentucky, Department of Animal & Food Sciences, FSC 434

1. True (T) or False (F) (2 pts. Each)

Trypsin cleaves peptide bonds on the amine side of Lysine and Arginine.

Water is liberated when trypsin cleaves peptide bonds.

Emulsions of fat in water generally have a higher concentration of lipophilic odor compounds in the head-space compared to a comparable mixture of without the fat.

Coenzymes are often comprised of water soluble vitamins.

Phospholipases are classified as hydrolases.

 The lipoxygenase enzymes contains copper at their active site.

Beta-carotene contains vitamin A activity.

Folic acid degradation usually involves bond cleavage at the C⁹-N¹⁰ position.

Thiamine (Vitamin B₁) is stable in an alkaline environment .

Chlorophyll is classified as a water soluble pigment.

 Aroma compounds bind to proteins by hydrophobic interactions.

2. Knowing the mechanism of the catalytic triad of serine proteases and that a similar mechanism is employed in lipases, diagram a likely step-by-step hydrolysis of a fatty acid from a triglyceride by a lipase. Be sure to show the enzyme acylation, transition intermediate and deacylation steps. Label each step. (10 pts.)

3. What is the purpose of malting barely for the brewing industry (3 pts).

4. What are two distinct differences between the activity of Lipoxygenase I and Lipoxygenase II? (4 pts).

5. Contrast the relative rate of antioxidant activity of "-tocopherol compared to other tocopherols in a food system and in a living-biological system. Give a plausible explanation for your answer. (5 pts)

6. Characterize the conversion of ascorbic acid to dehydroascorbic acid. How does this conversion effect vitamin C activity? (4 pts).

7. Describe the changes of Chlorophyll to Pheophytin and Chlorophyllide. How do these changes effect the color of foods. (4 pts).

8. What is the major difference between the hydrocarbon carotenes and xanthophylls. What is the main structural feature that contributes to their color. (4 pts).

9. Describe the characteristic of anthocyanins that allows them to be easily distinguished from other pigments of similar color? (4 pts).

10. Contrast deoxymyoglobin, oxymyoglobin and metmyoglobin with regard to their structure and color. (6 pts).

11. Describe the structural basis for the most widely accepted theory of sweet receptors. (6 pts).

12. Define Aroma Value. (2 pts).