Vitamin C is a fragile micronutrient [1,2]. Any manipulation of the fruit which contains it, can destroy it.
Let's talk for orange juice, for example.
Virtually, staring with harvesting of the orange, vitamin C degrades.
And this trend continues due to mechanical (squeezing), thermal (pasteurisation) and chemical (adding preservatives) treatments when the orange juice is made.
Furthermore one should take into account orange juice that has been placed into a bottle, stays on the supermarket shelf for weeks, after it has been transported from the made factory to the supermarket.
And the question born of your own accord: how much of the vitamin C listed in the nutritional label is actually in the orange juice I drink?
Long story short: how much vitamin C is actually present in a glass of orange juice, taking into account could have been passed months since harvesting-squeezing-bottling to drinking?
Is the nutritional label correct?
This question worth for other vitamins and other susceptible micronutrients in other foods, as well.