Disadvantages of Canned Vegetables
The main disadvantage is the loss of nutrients in canned vegetables. Although heat kills germs and preserves the vegetable, it also affects the nutrient content of the product.
In addition to heat treatment, preliminary operations to canning (trimming, washing, peeling) can also have a definite effect on nutrient content. For example, canned tomatoes need to be peeled. This is done by alkaline treatment of the tomatoes. Although this treatment enhances peeling, it also produces a loss of labile vitamins such as folate, ascorbic acid, and thiamin. Blanching, another preliminary operation, also produces losses of vitamins.
Lund (1988) studied the loss of essential nutrients in canned vegetables. For example, green peas lost 78% of biotin, 59% of folate, 69% of vitamin B6, and 5% of thiamin. Carrots lost 75% of vitamin C and 80% of vitamin B6. More than 50% of biotin, folate, and vitamin B6 are lost in canned tomatoes.
The elevated temperatures experiences by canned vegetables accelerate reactions that would otherwise occur more slowly. This is the reason of loss of essential nutrients in canned vegetables. The particular losses of canned vegetable will depend of a multitude of factors: the nature of the food, the chemical composition, the pH of the environment in which the vegetable is canned, the presence of pro-oxidants and anti-oxidants, and so forth.