Daniel L. Schadler and Anna A. George
Department of Biology, Oglethorpe University, Atlanta, Georgia 30319
Answers to Questions:
Q. 1. The procedure described here for production of methyl salicylate involves an overall reaction that includes two acid-catalyzed transesterification reactions between aspirin (acetylsalicylic acid) and methanol. Draw the structures of the reactants and products of the overall reaction.
See Figure below
2. The transesterification reactions described in Question 1 are equilibrium dependent. Why, then, is the use of a large excess of methanol important in the overall reaction?
Since the reaction is equilibrium dependent, the large excess of methanol will drive the reaction toward the synthesis of methyl salicylate and methyl acetate. Methanol is both the solvent and a reactant in the reaction. By the law of mass action, the large amount of methanol forces the reaction toward the right in the reaction as shown in the answer to Question 1.
3. It is reasonable to hypothesize that fungistasis is a proportional phenomenon; that is, exposure to a larger amount of a fungistatic agent will induce greater inhibition than exposure to a lesser amount. How would you test this hypothesis using the bioassay procedure described here?
To test if fungistasis is a proportional phenomenon, the experimenter could vary the exposure of a fungus to the fungistatic agent in a systematically increasing manner. For example, using the procedure described in this exercise, a control with no fungistatic agent would be set up, then treatment exposures to 1, 5, 10, 15, etc. microliter amounts of the fungistatic agent. If the phenomenon is proportion, then the growth of the fungus should decrease with increasing exposure to the agent. If fungistasis shows a threshold effect, however, no growth inhibition would occur until a critical amount of the agent was used.
4. As noted in the Introduction, it may be possible to use volatile oils to control post harvest diseases of fresh produce such as fresh fruits and vegetables. What problems do you think would be encountered when attempting to put this into practice; consider both the culinary art and the food science perspectives.
There is not a single correct answer to this question; students will likely propose some that show even more creativity and insight than the one offered here.
One problem that may be encountered when using volatile oils to control post harvest diseases in plants is ensuring treatments that are thorough enough to control the disease. Adequate exposure times and treatment concentrations would have to be determined. The removal of the volatile oil would also have to be considered, since any residual material may give the food an odor or a taste that would be unacceptable to consumers. On the other hand, fruits or vegetables with novel odors or tastes may find a niche market that would be successful for them.
