Well, not exactly, but the heat treatment used before freezing is. As we reported back in April of this year and in 2011, broccoli has cancer fighting abilities in the form of sulforaphane which comes from the conversion of glucoraphanin with the enzyme myrosinase.
Unfortunately, before broccoli is frozen it is heat treated (blanched) to inactivate enzymes that, among other things, can cause off flavours to develop. This treatment also destroys the enzyme myrosinase that is needed to form sulforaphane.
But help is at hand, scientists from Illinois have developed two ways to allow the broccoli to keep its anti cancer abilities. One way is to reduce the temperature used for blanching. By reducing it from the recommended 86°C to 76°C, they preserved 82% of the enzyme. In another experiment, they added additional myrosinase from the related daikon radish. The percentage used was so small that taste was not affected but sulforaphane was produced.
The scientists hope that this will lead to a change in the processing of frozen broccoli, but until that time they recommend supplementing the broccoli with small amounts of raw vegetables that produce the enzyme such as radishes, cabbage, cress, horse radish (to name but a few).