Chem 336 - Spring 2002
Organic Chemistry III
Dr. Carl C. Wamser
Carey, pages 1045 - 1050:
Problems 26.15 - 30
1. Olestra, a new fat substitute, is considered a sucrose polyester, where the carboxylic acid groups are fatty acids. Write out a possible structure (or look it up). What aspects of its structure are like a typical fat?
It's considered low-calorie only because it doesn't get digested easily. If it were digested (completely hydrolyzed), what would the products be?
Olestra has a mix of fatty acids attached
to the OH groups of sucrose (typically 6 - 8 fatty acid esters
groups). This resembles the usual triglyceride structure for fats,
so it has a similar "mouth feel", and it behaves similarly
in cooking - even less likely than fats to break down on heating.
If our digestive enzymes could break it down, it would give sucrose
(and then glucose plus fructose) and 6 - 8 fatty acids. Per mole,
it would contain more energy than a typical triglyceride because
it has more fatty acids. Per gram, however, it would be about
the same as fats, since the great majority of the weight in both
molecules is the fatty acid chains.
A concern about Olestra is that it may act as a nonpolar, water-insoluble
medium that absorbs other important nonpolar nutrients (especially
Vitamins A and K) and escorts them out of the digestive tract
rather than allowing them to be absorbed.