Instead of loss of "nutrition" I should have said loss of "quality" (color, flavor and texture). Sorry ...
As for fresh vegetables ... yes, they should be blanched before freezing to kill bacteria and decay causing enzymes (this is what I was thinking about when I said loss of nutrition). Yes, there is some nutritional loss when blanching (even more if not done properly) but then some nutritional loss is inevitable in cooking anyway! Yes, frozen vegetables are more nutritious and taste better than canned vegetables - the go from the field and are blanched and quick frozen at their "peak" - and do not undergo the "cooking" that canned vegetables undergo during the canning process.
Freezer burn is caused by dehydration and ice crystal formation on the surface of frozen foods not sealed in an airtight "vapor proof" package. It results in a loss of food quality and off flavors. This is why vacuum sealed foods can last so long without appreciable loss of quality or developing freezer burn. The more vapor proof the packaging (why you would want to use Freezer bags instead of other plastic bags) and the less air the better.
The National Center for Home Food Preservation has a good FAQ on Freezing
foods and a How To
freeze various foods section. You might also find this article on Safe Home Food Storage
of interest since it gives a lot of information on safe pantry/refrigerator/freezer storage of a variety of foods. And, here is a How To
site about vacuum sealing - not too comprehensive but good basic info.
A lot of which method you use will depend on for how long you want to store the food.