Very soon, summer farmers’ markets will be re-appearing, and lots of local fruits and veggies will be here for us to enjoy again. But right now, you may be relying on frozen or canned, or getting fresh ones at the supermarket that have traveled many miles to get here. And you may be wondering, what’s best nutritionally in the colder months…fresh from afar, or frozen/canned?
What makes fruits and veggies so good for you, and how can they lose those good things after harvest? The nutrients that they have in abundance are vitamins A and C, folic acid (one of the B vitamins), potassium, anti-oxidants, and fiber. These nutrients can “get lost” by leaching into water (in processing and cooking), and by chemically changing.
Common sense tells us that, if you pick a tomato, rinse it and eat it, there’s very little loss of anything. It tastes, looks, and smells best then, too…a delight for the senses! So, it’s always best to eat fresh, just picked produce. Of course, we can’t always do that.
Vitamin C is by far the most delicate nutrient. It begins to degrade almost immediately after harvest. So we lose some no matter what (unless we eat that tomato right off the vine!). Some fresh veggies have lost half their vitamin C after 48 hours. Often 50% or more is lost in the freezing and canning process. But take heart! Some veggies, such as broccoli, red pepper, tomatoes and leafy greens are such good sources that even after that loss, they still have plenty to spare. And once frozen or canned, further losses are minimal; however, if fresh veggies are left to languish in the fridge for a week, some can lose all of their vitamin C!
B vitamins are also water soluble, and some folic acid is lost after harvest, but its nickname is “the foliage vitamin”; leafy greens can stand losses because they have a lot.
Good news about anti-oxidants …some of them actually increase after the produce is harvested. Also, heat treating before canning and freezing can give them a boost. They are in high concentrations in the peels, so if the edible peel is removed in processing, some anti-oxidants are removed also.
Vitamin A as beta-carotene, fiber and potassium are more stable nutrients, and so are less likely to decrease during processing or shipping.
Here are some tips to help you take this info to the produce aisles (or gardens):
- Fresh is definitely best if eaten within 24-48 hours of harvest. So, when the weather warms, get thee to the farmers’ market, CSA, or your own backyard garden!
- If fresh produce is older than 48 hours from harvest, it may have less of some vitamins than frozen or canned. Of course you can eat it anyway, unless it’s visibly slimy or moldy. It will still have some vitamin content, and it will have anti-oxidants, potassium and fiber. Definitely much better than not eating any!
- If you cook veggies in water, use the cooking water, in soup or another recipe.
- Watch the sodium in canned veggies. Get “no salt added” varieties or get frozen, which doesn’t have added sodium.
Maryann Ludlow, RD, CD, CDE, is a registered dietitian at the UVM Medical Center.