[lathyrus_long]

Sophisticated growers routinely get lab tests that provide a breakdown by element of the leaves, fruit, or other parts of the plant. This is mostly to assess plant health, but also gives an indication of the nutritional value to humans.

It's possible to manipulate the element breakdown of the edible parts of the plant over a surprisingly wide range with an appropriate nutrient solution. For example, they grow low-potassium vegetables for people at risk of hyperkalemia:

https://www.mdpi.com/2311-7524/7/4/87/pdf

Of course the lab test doesn't indicate whether the elements are in a form available to humans. I'm not aware of any biochemical mechanisms by which hydroponic vegetables with the same element breakdown would be less nutritious, though I'm not sure how you'd prove none exist.