There are some who claim that new varieties of vegetables have fewer nutrients than heirloom varieties. In a recent study at the USDA Vegetable Lab in Charleston SC, Mark Farnham and Michael Grusak grew out several broccoli varieties (number unknown) but included heirlooms as well as a series of new varieties released over the last 30 years.
They were looking for trends and differences between the crops and years of introduction.
The study looked at concentrations of calcium, copper, iron, potassium, magnesium, manganese, molybdenum, phosphorus, sulfur, and zinc.
Nothing consistent over the years.
In some years and with some minerals the older varieties had higher concentrations and in other years, the newer hybrids had higher concentrations. So it depends on the year, the cultivar and the specific mineral.
Myth-busters says – false – newer varieties are equal in mineral concentrations as older heirlooms and this hasn’t been bred out of them.