“Frozen food” is a really broad category, including everything from freeze-dried fruits and vegetables to pre-processed meals. I plan on just discussing the effects of freezing on produce, because I think this is something relevant to the lives of a lot of people.
As a friend of mine who lives alone said: “if there’s no negative impact on freezing foods, then I’d waste less and save money.” For anyone who is already constantly powering a refrigerator/freezer combo, the difference between being able to use all of your carrots or chilli-peppers instead of throwing a few out once they go bad is dependant on whether you put them in the freezer. So, the question of how well these frozen foods maintain their nutritional values is a pertinent question.
Everyone knows that freezing turns the water in the cells into ice crystals, essentially rupturing the frozen membranes. This temperature based physical change deactivate all the enzymes (protein based engines of change in all life) and all bacteria currently living on the fruit/vegetable. This is both a good, and a not so good, thing.
The upside to freezing is that it better preserves nutrients and antioxidants in your food. The downside is that you rupture the cells and deactivate the plant’s remaining molecular protectors, meaning that once thawed it will go bad much more quickly.
A 2002-2005 study under Dr.Steinhart at Hamburg University analysed the effects of different types of storage and drying conditions on nutrient, ß-carotene, and antioxidant levels. A number of tests on ß-carotene levels found no significant differences between treatments, regardless of temperature. But, when they examined antioxidants, they found that after 2 weeks the frozen produce had significantly higher levels of antioxidants than those that had been kept at 4 degrees Celsius. Beans that were stored at -18 degrees Celsius for 4 months had higher average levels of antioxidants as those kept 7 days at room temperature. Nutrients remained more stable, over time, in frozen treatments than in those stored at temperatures above 0.
In general, freezing foods helps preserve their antioxidant and nutrient levels. You effectively prevent oxidation,and also digestion by bacteria and fungus, by keeping them below freezing. Freeze-dried foods, which are dried via freezing to make them keep longer, do not have the benefits of foods kept in freezing temperatures: they do not have higher levels of antioxidants or carotenoids.
This general tendency isn’t just true for produce, but also holds true with human breast milk. When you freeze something: you freeze it in its current state and deactivate all cellular machinery. The only downside is that it will go bad more quickly once thawed: keep in mind that freezing ruptures the cells since ice is less dense than water.
Ecologically, what is the impact of frozen food? Well, it takes a lot more energy to freeze, and keep frozen, than if it is consumed fresh. But, our world is not based on ideals, but instead realities. The reality is that a lot of food goes bad because it sits around, and that many of us have largely empty freezers where we could put produce we already buy but don’t use very often. If your money is short: don’t feel ashamed or guilty for feeding your family frozen fruits or vegetables.
I would certainly have thrown out fewer carrots and chili peppers, had I known about this earlier. I still prefer fresh produce, and it certainly has fewer logistical costs compared to buying anything from the frozen food aisle, but I now know there are even certain advantages to frozen food.
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