9 Interpret your results: a In which tube(s) did protein digestion occur? How do you know? b In which tube(s) did no protein digestion occur? How do you know? c What effect does pH have on protein digestion with pepsin? Why? d What other effects does acid have in the stomach? Procedure 3 Demonstrate Lipid Emulsification Let’s examine what happens during the process of emulsification. In this exercise you will use four substances to observe emulsification in action: 1 Lipids: The source of lipids for this exercise is vegetable oil. Emulsifying agent: Detergents are considered to be emulsifiers because they have both polar parts and nonpolar parts, similar to bile salts. The emulsifying agent in this exercise will be a liquid detergent. Distilled water. Sudan red stain: This is a stain that binds only to lipids. The sole purpose of this stain is to make the lipids more visible during the procedure. Safety Note 1 Obtain a glass test tube and add approximately 2 ml. of distilled water to it. Safety glasses and gloves are required! 2 Add about 2 ml. of vegetable oil to the water. 3 Place a rubber stopper into the tube and shake it vigorously for 15 seconds. Allow it to stand for 2 minutes. What happens to the oil and water? А 4 Add three or four drops of Sudan red stain, and shake the tube again for 15 seconds. What color is the oil? What color is the water? 5 Add about 1 ml. of liquid detergent to the mixture and shake the tube vigorously for 15 seconds. Allow the tube to stand for 2 minutes. What has happened to the solution? Is it still two distinct colors? Explain your results.