AboutJohn Locke Expertise I will answer all biology-related questions through the undergraduate level. I will explain unclear concepts and suggest approaches to solving problems, but would prefer not to completely solve homework problems for you. If you are completely stumped on homework, tell me what you already know and I will help you as much as possible. Please do not ask me for ideas on school research projects; part of research is determining a suitable area of investigation, and that's not a task that should be completed by someone else.
Experience I have a BS in Bioengineering with a concentration in Chemical Engineering (which included a heavy focus on biology), and have taught biology, biochemistry, and related subjects for some time now.
Education/Credentials BS Bioengineering, Penn State University
MCAT/DAT/OAT Instructor
We have been doing an experiment on preserving apples. We put a half an apple in lemon juice, water with citris acid, water and in an air tight bag.(We also had a control.) we are unsure why the apple which was in the water went brown at the edge of the flesh- it was about a mm thick... WE are also unsure why the apple in the citris acid turned pink at the edge of the skin. And why the apple in the lemon juice went slimy. Can you help us with these questions?
Thanks
Monique, Heath, and Jack.
Answer I can answer some of your questions broadly, but I unfortunately cannot determine the exact reason for all of the observed results. The apple in plain water turned brown due to normal oxidation, which is the same process that would occur had the apple been left in an open air environment. Being in water slowed down the oxidation process a lot--the water you were using almost certainly had less oxygen in it than air, and it's the reaction with oxygen that is responsible for fruit turning brown. Nonetheless, the organic acids within the apple did react with some oxygen and thus became oxidized. This process also involves the enzyme polyphenol oxidase: http://recipes.howstuffworks.com/question168.htm
I'm not entirely sure why placing the fruit in citric acid caused it to turn pink. I can tell you that the fruit does not brown when placed in citric acid because the citric acid reacts with oxygen instead of the apple (this makes it an antioxidant, and you may be familiar with ascorbic acid being marketed as an antioxidant). The apple became slimy when placed in the lemon juice because of various substances within the lemon juice. If there was any pulp in the lemon juice at all, that would adhere to the apple and produce a slimy surface coat. I doubt that any chemical reaction occurred--it was simply a case of material from the lemon juice adhering to the fruit surface.
