Your intake of polyphenols is one of the mandatory pillar of durable health.
Polyphenols are part of the natural defenses of plants.
Plants which grow in a low bacterial fungus and insect environment do not need polyphenols and consequently synthesize less polyphenols than plants in the wild or in organic farming.
Carbonaro, M., & Mattera. M. (2001). Polyphenoloxidase activity and polyphenol levels in organically and conventionally grown peach (Prunus persica L., cv. Regina bianca) and pear (Pyrus communis L., cv. Williams). Food Chemistry, 72, 419-424.