I love a glass of orange juice with my breakfast, but I also tend to practice good oral hygine. Why does orange juice leave a hideous taste in my mouth if I drink it after I brush my teeth? It’s obviuosly some kind of chemical reaction (it tastes sulphur-ish), but what exactly is it?
I notice the hideous taste when drinking OJ after eating anything sweet (OJ after pancakes with syrup is abomidable).
I think the same mechanism underlies your OJ after toothpaste example.
OJ is sweet, but not overly so. It’s also very acidic, giving it a sour flavor. Perhaps if consumed after a very sweet item (syrup, toothpaste), the desensitized sweet receptors underreport to the brain’s taste center. At the same time, it business as usual for the sour receptors. And once this is neurologically integrated (not enough sweet, sour as usual) the result is that god-awful sour taste.
You shouldn’t be drinking it after brushing.
OJ is acidic (citric acid) and can damage the enamel. So brush your teeth after drinking it, as you should, and you won’t have any off-taste.
Down under they seem to agree that SDS (sodium lauryl sulphate, or sodium dodecyl sulphate) in the toothpaste desensitizes your sweet tastebuds.
http://www.publish.csiro.au/cyberscience/helix/TH49/TH49B1.htm
http://www.scifest.org.nz/bumpinto/experiments.htm
With just the sour and bitter tastebuds working, the orangejuice tastes extra sour and bitter after brushing.
SDS can also be found in most liquid soaps, so orange juice will also taste bad if you first gargle with shampoo 
Try beer after brushing your teeth! Now that’s yucky! That’s why I gave up brushing my teeth long time ago. or did you expect me to give up beer?
You dense people. Why brush your teeth BEFORE you drink something with sugar and citric acid in it??? That has to be the most pointless thing you can do.
You should have your breakfast, then brush your teeth. But you’re best to wait 20-30 minutes after your food before you brush.
Interestingly, barbitu8 managed to make this same point without calling our fellow members “dense.”
Yes he did, but I thought it was common knowledge. Sorry if I offended anyone.
There are toothpastes and mouthwashes out there that don’t contain the offensive chemicals (particularly saccharin) - use those and drink away.