There is no doubt that processed and canned fruits are safe, tasty, affordable and convenient. Consumers can have access to these products any time, regardless of geography, but are they also as nutritious as fresh fruits and vegetables? Factually speaking, both fresh produce and processed fruits and vegetables show nutrient loss when they undergo transportation and storage. Cooking destroys nutrients further, depending on the cooking method used and type of produce. So, can processed products really retain nutrition?
It is a fact that fruits and vegetables are almost 90% water, and once they have been harvested, they undergo moisture loss, deterioration and some amount of microbial spoilage. The moment the produce is harvested it loses its source of nutrients, the plant or tree, and so fresh fruits and vegetables begin to use their own nutrients. This is the reason that fresh produce has a very short shelf life and soon become unsafe and unfit for consumption. Since fruits and vegetables are so perishable, processing technologies have been developed so they can remain safe and stable and have longer shelf lives. Processes like freezing, canning and drying transform fruits and vegetables into processed products, and as happens with cooking, processing also leads to some amount of nutrient loss.
Several studies corroborate storing, cooking and processing all have a detrimental effect on the nutritional quality of fruits and vegetables. However, processing has other advantages because it arrests moisture loss, stops the produce from consuming its own nutrition and prevents microbiological growth. While processing is beneficial in these areas it also sometimes results in changes like loss of colour, texture, flavour as also nutritional quality as stated. Also, several steps taken prior to processing like washing, peeling and blanching cause loss of water-soluble nutrients. Nutrients may also be lost through oxidation, especially during heat treatment and storage. Nutrients like ascorbic acid (vitamin C) and thiamine are heat sensitive and so get lost during processing. Vitamins are also lost because of thermal processing. Removing the skin can also reduce mineral content of canned produce.
Retention of Ascorbic acid or vitamin C in a product, after it has been processed, is the gauge that helps measure nutrient quality. Ascorbic acid is used to estimate the nutrition loss as it is one of the most unstable nutrients during processing. It is affected by oxidation and leaches into water soluble media during processing, storage and cooking. On the other hand, other vitamins and minerals are more stable particularly Vitamin A and E. There are several studies which show that the initial thermal treatment of processed products can cause loss of vitamin C and B. However, they do become stable once the canned products are stored because of the lack of oxygen within the cans. Just like Vitamin C and B which are water-soluble and oxygen-labile, phenolic compounds too can change depending on the variety of fruits and vegetables. However, what is interesting to note is that Vitamin C losses during storage of canned goods tend to be quite small, when compared with storage losses in fresh and frozen products.
There are several scientific journals that point out that canned, frozen and fresh fruits are all nutritionally at par. In fact, some canned products could be more nutritious like canned tomatoes, which contain more lycopene and vitamin B, as compared to fresh tomatoes. Canning also helps to make fibre in beans more soluble allowing the body to absorb it better. High-heat canning, a method used for preserving food, prevents the growth of microorganisms and so makes them safer than fresh fruits and vegetables, which are anyway likely to lose nutrients during storage and cooking. Therefore, we could say that high heat canning process preserves foods better.
Fresh produce might be best because it offers quantity and a variety of nutrients but it has to be really fresh. If the fruits and vegetables have been sitting on the shelves for long, then it is likely that they have lost vitamins and phytonutrients. Fresh produce that comes straight out of the farm, and directly to you, has the most nutritional value. However, consuming frozen or canned fruits and vegetables also provide fairly good amounts of nutrients. In fact, the Centers for Disease Control and Prevention state that all fresh, frozen, dried or canned fruits and vegetables can count towards the five, fruits and vegetables a day goal, if they have no added sugars or fats or excessive sodium.