Vegetables/Fruits fresh from the farm or just picked are healthier than frozen or canned ones. Frozenand Canned vegetables can still be a good choice. They need to be canned or frozen right after being harvested, when they still have all of their healthy nutrients.
Keep in mind how much salt is added to canned vegetables. Try to buy those without added salt. And, don’t overcook any vegetable, whether fresh, frozen, or canned. Instead of boiling them in water for longer periods of time, they should be lightly steamed.
Freezing food stops this nutritional depletion. As food freezes, moisture inside and outside it forms ice crystals. The slower something freezes, the bigger the ice crystals become — and the more damage they do to the structure of food, and therefore its flavour.
Study finds two out of three foods found to have more nutrients if frozen – probably (kidding ~ no source)
Broccoli : Frozen broccoli had higher levels of vitamin C and lutein and four times more betacarotene.
Carrots : Frozen carrots contained three times more lutein, twice as much betacarotene and more vitamin C and polyphenols than fresh.
Blueberries : Frozen had more vitamin C, polyphenols and anthocyanins
Peas and sweet corn : No significant difference found between frozen and fresh.