4
$\begingroup$

I recently purchased Dextrose from a local bulkfood store. I want to use it instead of table sugar. My concern is that it may be l-glucose instead of d-glucose. According to Wikipedia l-glucose is too expensive to produce but l-glucose produces laxative effects which is what I'm experiencing when I consume this dextrose.

Any tests I can do to check if it's truly d-glucose?

$\endgroup$
1

1 Answer 1

5
$\begingroup$

The canonical experiment is to measure the optical activity (rotation of plane polarized light) by a solution of the substance. Dextrose, unsurprisingly, is dextrorotatory (rotates light to the "right"). l-glucose is levorotatory (rotates to the "left"). Two things to keep in mind: There are different d and l nomenclatures. A compound labeled "D-" is not always dextrorotatory.) Also, optical activity is only definitive if you've already established the compound is d-/l-glucose. If it's fructose ("levulose") or some other carbohydrate, the normally occuring isomer could be the levorotatry one.

Given that you likely don't have a polarimeter handy, another easy experiment you can do is to add some yeast to a weak solution of the sugar. Yeast can readily use d-glucose, but should have a difficult time fermenting l-glucose. The reason for this is that the enzymes which catalyze the utilization of glucose are chiral, and will only match the typical d- configuration. l-glucose won't fit, like a left foot doesn't fit well into a right shoe.

All that said, it's so exceedingly unlikely that you were sold l-glucose that it boggles the mind. First off, there's the labeling concern. "Dextrose" specifically means the d- isomer, so anyone selling l-glucose as dextrose is committing fraud. Secondly, the price differential is astronomical. Spot checking, from a chemical supplier l-glucose costs over \$50 per gram (so ~\$400 per teaspoon). In comparison, d-glucose of a similar grade from the same supplier is around \$0.04 per gram (so \$0.30 per teaspoon). With over a thousand-fold price differential, someone along the way would recognize if they were accidentally selling l-glucose.

$\endgroup$
1
  • $\begingroup$ Ok, then I should be sound assuming that I'm consuming d-glucose. I am going to try the yeast trick eventually. Thank you R.M. $\endgroup$
    – user8893
    Apr 14, 2016 at 15:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.