I enjoyed a couple of brussel sprouts myself for dinner tonight. Not sure if they had experienced frost in their lives but tasted OK to me and they are definitely best in winter.
Here's some confirmation:
"A few of these vegetables actually react to cold conditions and frost by producing sugars, which make these notoriously bitter vegetables taste rather sweet. Brussels sprouts and kale show this characteristic most prominently. ... Some root vegetables also become sweeter after a few frosts."
