If you can't find fresh vegetables or are looking for produce that is not in season, frozen is a good alternative. Frozen vegetables are picked at the peak of ripeness, then blanched and flash-frozen to remove bacteria and lock in their essential vitamins and nutrients. The faster they are frozen after picking, the more nutrients they will retain. Plus, while fresh veggies have a lifespan of only a week to two at best, frozen veggies can last much longer in the safety of your freezer. For the most nutritious frozen fruits and veggies, select varieties prepared with little or no added salt, sugar or syrup and avoid choices with breading and sauces.
Canned vegetables can lose some of their vitamin C in the heating process during canning but when they are handled and canned quickly, much like frozen foods, the majority of nutrients are locked in and retained. If you opt for canned, do not purchase or use cans with dents, cracks, rust, punctures, or bulges, these are signs that the food inside could be unsafe. Immediately discard a canned product if it shows signs of swelling or it there's leaking from the can.