Unripe oranges Id say.
Apples juiced are often unripe too/you just drinking it faster than you could eat it.
Unripe oranges are also a pain for sensitive teeth. I learned it the hard way.
In part because juicing leaves behind concentrated antinutrients, skin eruptions and canker sores are a common problem. We do not recommend juicing on a regular basis.
for some people the acidity of orange juice is enough to give them canker sores. My father gets them if he drinks oj. That doesn't stop him but he just knows that his mouth's lining just might be a little more sensitive than other peoples'. Maybe he produces less saliva than others so the natural rinse may not happen as quickly either. who knows but I just assume that everyone is not made the same. You just might be a little more sensitive to the acid level of the juice.