When you're in a hurry and busy, you don't always have time to use fresh foods and commit to preparing a meal.
Who has never wondered, then, whether it's better to go for canned vegetables, frozen, vegetables or not to eat vegetables at all?
Some say that fruits and vegetables retain their richness in vitamins and antioxidants if they are not kept for more than 3 days in the refrigerator. This is confirmed by 2 British studies: frozen products would often be preferable, from a nutritional point of view, to fresh fruits and vegetables that would have been in the refrigerator for more than 3 days. The trouble is that both of these studies were commissioned by a British trade organization, the frozen food organization.
The fiber, vitamins, minerals, antioxidant molecules and other active molecules in fruits and vegetables are affected by storage conditions anyway. Thus, water-soluble phenolic compounds are sensitive to oxidation and inevitably degrade in both the freezer and the refrigerator. Freezing appears to reduce the nutrient concentrations of vegetables, as they are blanched (= heated) before being frozen.
The British Frozen Food Federation commissioned a report from Leatherhead Food Research (1) and the University of Chester (2) to assess the impact of storage conditions on fresh and frozen fruit and vegetables.
The researchers analyzed products purchased in British supermarkets. Fresh produce was stored in a refrigerator at 4°C for 3 days, and frozen produce was stored in the freezer at -20°C, replicating the rhythm of a consumer who would shop twice a week. After preservation, the researchers analyzed their content in vitamin C, polyphenols, anthocyanins, lutein and beta-carotene.
Results: concentrations measured in frozen produce were similar to those of fresh produce before refrigerated storage. In contrast, vitamin and antioxidant concentrations had declined during their refrigerated storage to levels often below those of frozen produce. This loss was particularly marked for berries. For example, fresh blueberries had vitamin C levels above 50 mg/kg, while after being stored for 3 days in the refrigerator, the level was only 20 mg/kg. In 2/3 of the cases, frozen fruits demonstrated higher antioxidant concentrations than fruits and vegetables stored for 3 days in the refrigerator.
According to Rachel Burch (Leatherhead Food Research), author of one of the studies, the results "show that frozen products can be nutritionally comparable to fresh produce before storage." The authors state that the loss of nutritional quality due to preservation is probably greater than consumers realize.
Unfortunately, in stores, whether fresh or frozen, there is no way to verify how long they have been stored in the freezers or on the shelves, but chances are that between harvest and arrival in the store, it has already been more than 3 days...
Of course, you'll have a better chance of getting the benefits of fresh fruits and vegetables if you shop more often.
In conclusion, eating fresh fruits and vegetables as soon as possible after harvesting is the best option, but unfortunately it is not always feasible in everyday life.
Unless you have your own vegetable garden or orchard.
Failing that, it's best to opt for frozen products it seems which is the "best" alternative.
Sources:
(1) R. Burch. Nutritional content of fresh vs frozen foods. Leatherhead Food Research. 19/04/2013.
(2) G. Bonwick and C. S. Birch. Antioxidants in Fresh and Frozen Fruit and Vegetables: Impact Study of Varying Storage Conditions. University of Chester.