“Consumers tend to have the impression that fresh is generally superior to frozen, but that assumption is misplaced,” Ronald Pegg, study co-author and associate professor at The University of Georgia College of Agricultural & Environmental Sciences, told FoodNavigator-USA.
For the study, titled "Nutritional comparison of fresh, fresh stored and frozen fruits and vegetables: Vitamin C, Vitamin A, Folate and Minerals," fresh and private-label frozen blueberries, strawberries, broccoli, green beans, corn, spinach, cauliflower, and green peas were purchased from six local supermarkets over a two-year period. A composite sample of each fruit or vegetable was prepared with equal quantities of the produce from each supermarket. Fresh produce was analyzed for nutrients on the purchase day and again after five days of storage in a kitchen refrigerator, to mimic consumers’ typical purchasing and storage habits of fresh produce.
Vitamins C, A, and folate proved to be susceptible to degradation by enzymatic and oxidative mechanisms in the fresh-stored versions, whereas minerals did not. And in most cases, the frozen produce was not statistically different from its fresh counterpart in terms of vitamin content.
If you put fresh produce in the fridge, it degrades over time and loses nutrients
Dr. Pegg said he wasn’t surprised by the study’s results, as he’s “always had the point of view that frozen was going to be similar to fresh,” though he was intrigued by the nutritional degradation of fresh-stored produce noted in each instance.
“What we did see, and this was interesting, that the vitamin content of samples stored in fridge for a little time, in every single case, always decreased from their fresh counterparts.
"And in many cases, the frozen version was superior to fresh-stored: be it in vitamin A, folate or vitamin C levels,” he said.
“If you put fresh produce into the refrigerator, this vegetable or fruit is a living material—it respires, there’s oxidation and enzymes operating. It degrades over time and loses nutrients. That’s normal and to be expected.
“Freezing in essence is nature’s pause button. It maintains freshness in what we call fresh foods, slows down enzymatic reactions, increases the time it takes for anything to degrade.”
Freezing is nature’s pause button
There were some small variations (e.g., vitamin C levels in fresh-stored and blanched, frozen spinach was significantly less than fresh; frozen green peas had significantly higher vitamin A levels than means of fresh and fresh-stored; and mean folate levels for blueberries, corn and green peas were significantly greater than their fresh-stored counterparts).
“The way the study was designed, we tried to reduce variability in that we prepared composite samples, went to six supermarkets, and purchased certain quantities of each,” Dr. Pegg said.
“But there is always some inherent variability. When a significant difference existed, such as frozen was superior to fresh-stored, that difference was not of huge magnitude. We’re not talking about a difference of 100 times. But it does bring back the message that frozen fruits and vegetables are not inherently different from their fresh counterparts.”