… frozen broccoli is generally higher in vitamins C and A as well as some antioxidants, compared to fresh broccoli that’s been sitting in your crisper for several days,
… frozen vegetables are blanched to help preserve color, safety, and texture, which can reduce water-soluble and heat-sensitive nutrients, including sulforaphane.
… to make frozen broccoli even more nutritious. “Chopping broccoli and letting it sit for about 30–40 minutes before cooking allows an enzyme called myrosinase to activate, which helps increase the formation of sulforaphane,” Hadley says. “Adding a small amount of mustard seed after cooking can also help boost sulforaphane production, making both fresh and frozen broccoli more nutritionally impactful.
https://www.realsimple.com/fresh-vs-frozen-broccoli-is-one-healthier-11894791