How do you freeze veg?
As Welshonion says, the methods vary, but just about always involve blanching in boiling water. Vegies contain enzymes that aid their maturing process. Freezing alone doesn't deactivate the enzymes and frozen raw vegies will continue to mature and (eventually) deteriorate even if at a slower rate. Blanching in boiling water effectively stuns the enzymes into inactivity meaning the veg should be - as it were - frozen in time.
After blanching, the veg has to be plunged into iced water to chill them, to stop them cooking. Then it's a matter of drying them completely, bagging them - removing as much air from the bag as you can - and freezing them, ideally as rapidly as possible.
The professionals work on an industrial scale with instant blanching, instant chilling, instant drying and snap-freezing. Home freezing doesn't produce the same results but I do it quite a lot with a more than satisfactory outcome.