Nutritional Differences Between Frozen & Fresh Vegetables

Are there nutritional differences between frozen and fresh vegetables and fruits? Interestingly, research shows that the nutritional differences between fresh and frozen produce depend largely on for how long you are planning to store the food in the fridge or refrigerator before you cook and eat it. In general, fresh produce starts to rapidly lose its nutritional value within hours after harvest. Fresh spinach, for example, loses 75% of its vitamin C within seven days of harvest when stored at stored in the refrigerator at 4°C (39°F).
Vegetables and fruits that are chosen for freezing, on the other hand, are typically blanched and frozen immediately after harvesting, which means they still have a high nutritional value when the blanching begins. However, the blanching process – which is used to deactivate spoilage-causing bacteria before the food is frozen; will cause loss of nutrients. This nutrient loss can vary significantly among different vegetables. The actual freezing will usually not have a significant impact on the nutritional value of the vegetables.
Let's look at some nutrition facts about common fresh vegetables and how they compare to their frozen counterparts:

Fresh vs. Frozen Broccoli

Vitamin C begins to degrade immediately after harvest. According to a study published in the journal Food Chemistry in 1998, fresh broccoli loses 56% of vitamin C (on a dry weight basis) during the first 7 days after picking if it is stored at 20°C (68°F). However, according to the same study, storing broccoli in the refrigerator at 4°C (39°F) can reduce the vitamin C loss to almost zero during the same seven day period.
According to a study published in the peer-reviewed Journal of the Science of Food and Agriculture in 2000, broccoli loses about 50-55% of its vitamin C content during blanching and subsequent freezing. Furthermore, a 1998 study published in the journal Food Chemistry found that frozen broccoli loses a further 10% of its vitamin C when stored at –20°C (–4°F) for 12 months.

Fresh vs. Frozen Green Beans

According to a UC Davis study, green beans can lose as much as 77% of their vitamin C content when stored at 4°C (39°F) for seven days. This loss will increase to a whopping 90% if the beans are stored for 16 days in the refrigerator, says a 1999 study published in the Journal of Food Science. In contrast, green beans lose only about 28% of vitamin C during blanching and subsequent freezing.
Whether fresh or frozen, green beans are a good source of carotene. Steam blanching is thought to result in little or no loss in beta-carotene, and according to a 1992 study published in the Journal of Food Quality, freezing will not have a significant effect on the beta-carotene content of green beans, either. The losses of beta-carotene are minimal also when fresh beans are stored in the refrigerator (around 10% on average when refrigerated for 16 days, according to a 1999 study published in the Journal of Food Science.

Fresh vs. Frozen Spinach

Even when refrigerated properly, the fine leaves of spinach lose their impeccable nutritional value very fast. Fresh spinach is an excellent source of folate, a nutrient many women are deficient in, but the vegetable starts to lose its folate the moment it is harvested. A 2004 study published in the journal Food Chemistry and Toxicology found that only 53% of folate in packaged spinach was retained after 8 days of storage at 4 °C (39°F). If the spinach was stored at 10 °C (50°F), the folate concentration was reduced to 23% already within six days.
When steam-blanched (instead of water-blanched) and frozen promptly after harvesting, spinach will retain much of its folate content.
If you only compare the folate concentration of fresh vs. frozen spinach, you will likely conclude that frozen spinach is the better option unless, of course, you are able to source spinach directly from a farmer. However, if you compare other nutrients in spinach, it is no longer clear that opting for the frozen product is the best way to go. Let's look at vitamin C: According to a study published in the journal Food Chemistry in 1998, fresh spinach loses 75% of its vitamin C when refrigerated for a week at 4°C (39°F). However, the loss of vitamin C will be almost equal (61% according to a study published in the International Journal for Vitamin and Nutrition Research) when spinach is blanched and frozen. Additionally, a 1998 study published in the journal Food Chemistry has shown that frozen spinach can lose a further 30% of its vitamin C if stored at –20°C (–4°F) for 12 months.

So What's the Conclusion?

Research shows that there are significant nutritional differences between frozen and fresh vegetables and fruits; however, it is difficult to prove any claims that one would be better than the other. If you are wondering whether you should choose a fresh vegetable or its frozen counterpart for your next healthy meal, make an estimate of how long it has been since the vegetable was harvested. Additionally, think about which vitamins and minerals that vegetable is famous for. Vitamin C, for example, is not as sensitive to the blanching and freezing process as it is to continued storage in the fridge.