Are fresh foods superior to canned and frozen? Well, for most of the time, fresh foods are the best in terms of quality (flavor, texture, and nutrients). This is almost true if you were the one who raised and harvested them, and the food in question is in season. But if the food is out of season, we would be dealing with produce that require transport and extended storage period. In most cases, additional process like canning or freezing has to be carried out. This is to ensure the produce reaches the customer without compromising quality.

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However, the common belief is that fresh, especially fresh-from-the-farm fruits and vegetables are always superior to canned and frozen. For this reason, most people opt for fresh produce. Well, the truth is that the difference is not significant. And there are some instances that frozen foods contain more vitamins and minerals than their fresh counterparts. The same thing can be said for canned foods.

Here’s how.

FLASH FREEZING OF PRODUCE AT ITS PEAK QUALITY

Fruits and vegetables are perishable food items. To prevent them from deteriorating quickly, they are usually flash frozen at the same location where harvested. Clarence Birdseye, an American inventor, developed the concept of flash freezing in 1942 when he was looking for a way to eat fresh vegetables during the winter. Flash freezing is a process whereby the food is subjected to extremely low temperature in just a few hours. In the case of vegetables, they are first washed and blanched prior to freezing. Blanching involves placing the vegetables in boiling water for several minutes to kill the harmful microorganisms.The process also helps preserve the color, texture, and flavor by deactivating enzymes. Enzyme activity speeds up the degradation of fruits and vegetables.

Blanching is generally not performed for fruits prior to flash freezing as the blanching temperature may adversely affect their quality. However, adding vitamin C or sugar to fruits prior to flash freezing helps slow down enzyme activity.

Because flash freezing reaches ultra low temperatures in a short period, only small ice crystals form. This reduces the damage to the cell membrane of the produce. And since the produce is frozen at its peak quality, the nutrients and minerals are retained and maintained. In some cases, produce that has been frozen can contain more vitamins and minerals as compared to fresh produce that has been transported for a long period, or displayed at the market or sitting in your kitchen prior to consumption.

In fact, this work studied vitamin retention between frozen and fresh fruits and vegetables. The study found no consistent differences between frozen and fresh. However, frozen blueberries, corn, and green beans contained more vitamin C than their fresh counterparts. Furthermore, frozen broccoli contained more riboflavin (B vitamin) than fresh.

CANNING INCREASES BIOAVAILABILITY OF SOME NUTRIENTS

Canning involves placing foods in jars and then heating them at a temperature that prevents the growth of harmful microorganisms. However, the temperature can also lead to losses in nutrients as the vitamins leech into the liquid. The same thing happens when we boil vegetables or fruits at home. Exposure to oxygen and light also affects nutrients negatively. But more is lost during processing that involves heat. This is especially true for fruits and vegetables rich in water-soluble vitamins and minerals. Vitamins C and B vitamins are particularly sensitive.

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But how much exactly is lost during canning though?

Well, the amount of nutrient loss is not that significantly different from that of produce not consumed immediately. Remember that a vegetable or fruit starts dying once removed from the mother plant. And in some instances, some canned foods contain more nutrients than fresh.

How?

The heating and cooking increase the bioavailability of some nutrients.

One good example of this is canned tomatoes, the most consumed vegetables in the United States. When canned, tomatoes can significantly increase its lycopene content. This work studied the effect of heat treatment on carotenoid (lycopene is a carotenoid) content of cherry tomatoes. Canned tomatoes increased its lycopene content two-folds. The canned tomatoes contained 11.60 mg/100 g of lycopene, whereas the raw tomatoes only contained 5.12 mg/100 g of lycopene. Lycopene is an antioxidant that helps reduce the risk of developing prostate cancer.

Cooking also have a similar positive effect in the heart-protecting carotenoid content in carrots, spinach, and cabbage.

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Fruits and vegetables are rich in nutrients. They contain vitamins, minerals, and plant chemicals that our bodies need to stay healthy. And a lot of these nutrients are not found in animal food. A good example of an essential nutrient is vitamin C. This vitamin is not sourced from animal food in significant amounts. And our bodies cannot synthesize vitamin C either. So a meat-based diet will not be sufficient. In order to consume an adequate amount of vitamin C, one must get it from fruits or vegetables, or otherwise from supplements.

But when it comes to the actual amount of nutrients, produce are at their peak just right after harvest. Detached from the mother plant, their nutrients gradually break down. According to Food and Agriculture Organization of the United (FAO), post-harvest losses of vitamin C in green vegetables can be high after a few days of storage. In fact, a 2007 study revealed that vegetables generally lose 15-77% of vitamin C a week after harvest. The rate of loss varies depending on the produce. One study found that mature spinach could lose up to 80% of vitamin C after 3 days. Nutrient loss accelerates if they are mishandled or exposed to elements such as heat and light during storage. But a lot of factors come into play, really.

Here’s how exactly fruits and vegetables lose nutrients over time.

Keep reading.

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HARVESTING AND RESPIRATION

The first thing that affects the freshness of fruits and vegetables is the manner they are harvested. Harvesting by machine increases the risk of damaging the produce. Many root vegetables are hardy, and they are usually harvested this way. Carrots, parsnips, and potatoes are usually harvested by machine.

Delicate vegetables such as tomatoes and salad leaves are easily damaged, which speeds up the nutrient loss. Harvesting by hand helps minimize the damage and increase the shelf life of produce. Since delicate vegetables are vulnerable to bruises and cuts, it is ideal to harvest them before fully ripe. Damage causes cells to break open, exposing the nutrients.

Ideally, fruits and vegetables must be harvested once they have reached their peak ripeness or desirability. At this stage, they are full of flavor and nutrients. They do not die after harvest though. This is very evident in onions, potatoes, and other root vegetables which sprout. They continue to respire, and take in oxygen for days, weeks or even longer. Some produce can stay notably fresh for longer periods. For example, potatoes can stay fresh in a cool, dark place for 3 months.

The main factor that dictates the rate of nutrient loss is the finite nutrients in store. After harvest, produce cannot replace organic materials such as carbohydrates and proteins. Fruits and vegetables use them up during respiration. During this process, the produce lose moisture and heat. This in return leaves us fewer nutrients once we consume it. The loss is much quicker in fruits and vegetables with higher respiration rates. Furthermore, the longer the produce respires, the more nutrients are lost. Sweet corn, mushrooms, asparagus, and peas have extremely high respiration rates. Aging follows once the nutrient reserves have been exhausted.

HEAT, OXYGEN, AND LIGHT

During processing, cooking, and storage, it is inevitable to expose the produce to many elements. Heat, oxygen, and light particularly accelerate the loss of nutrients. Many vitamins are sensitive to these elements. This is why cooking fruits and vegetables lose nutrients during cooking. More is lost when they are cooked in water. This is especially the case for water-soluble vitamins and minerals. Many vegetables could lose half of their vitamin C after boiling. Studies have shown that vitamin C and B vitamins are most sensitive. Fat-soluble vitamins D, E and K , fiber and minerals are less fragile and largely not affected by cooking.

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Not known to many, exposure to oxygen does affect the nutrients in fruits and vegetables. When cutting fruit or vegetable, the inside gets exposed to air. The apparent effect here is discoloration in fruits like apples and bananas. However, the presence of oxygen also affects many vitamins. Vitamins are antioxidants—they react to oxygen. And the longer a fruit or vegetable is exposed, the less vitamins it will have. Vitamin C is most the sensitive to oxidation.

Light also affects the nutrients in fruits and vegetables. B vitamins are especially sensitive to heat and light. However, the adverse effect is not always the case. A study by the U.S. Department of Agriculture (USDA) found out that spinach leaves exposed to continuous light were more nutrient-dense than those exposed to continuous dark. The light increased the amount of carotenoids and vitamins C, E, K and B9 (folate).

WAYS OF PREVENTING NUTRIENT LOSS IN FRUITS AND VEGETABLES

One of the most common ways of preserving nutrients of fruits and vegetables is storing in a low temperature environment. Most delicate vegetables should be chilled. The low temperature slows down physical and chemical reactions in the cells, thus protecting the nutrients. Storing broccoli at 32ºF (0ºC) for 7 days retains most of its vitamin C. If stored at 68ºF (20ºC), broccoli can only retain up to 44% of vitamin C. Transport vehicles have refrigerated facilities to provide a temperature-controlled environment. This keeps the produce as fresh as possible. In atmospherically-controlled facilities, fruits like pears and apples can remain fresh for up to 1 year.

However, the flavor of some hard vegetables such as potatoes, squash, onions can be affected by the chill air in the fridge. They will do fine in a cool, dark, ventilated area such as a cabinet or a kitchen pantry.

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Many people believe that fresh is better than frozen. It is true if the produce is for immediate consumption. Food grown and those purchased locally is superior in nutrition. However, if the produce takes time to reach the destination, it is better frozen than fresh. Vegetables that are frozen right after harvest tend to preserve more nutrients than their fresh counterparts. This is very helpful for produce that take several days before it reaches the store.

To fight nutrient loss against oxidation, one common way is storing fruits and vegetables in air-tight containers. This prevents the produce from being exposed to oxygen. When cutting fruits, cut them in large pieces. The less surface area that there is, the more nutrient that is retained.

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