All of us have some reservations about using frozen foods and quite rightly the fresh and juicy fruits and vegetables are irreplaceable. Only that busy and cost-conscious consumer can benefit somewhat from availability of frozen and canned foods. Like canned foods, frozen foods have a long shelf-life and are provided in a ready-to-eat form easy to use in meals. But, we cannot guarantee total retention of nutrients in frozen fruits and vegetables compared to fresh counterparts.
Why frozen is better than food that is allowed to freeze?
Temperature of freezing versus frozen vary.While freezing involves slightly higher temperature for longer time, the slow process allows formation of large ice crystals in the fruit or vegetable which destroys its cells leading to nutritional as well as textural losses. Whereas when foods are frozen, they are subjected to very low temperature for a short time that does not allow large ice crystals to form and maintain its maximum flavor, texture, and color after thawing.
Fruits and vegetables are highly perishable foods as they are a great food for microorganisms (full of nutrients) and undergo enzymatic and oxidative changes during storage. When fruits and vegetables are frozen microorganisms cannot grow, chemical reactions are reduced, and cellular metabolic reactions are delayed. Also , texture , flavor and nutritional properties are retained best in frozen fruits and vegetables compared to canned or dehydrated.
Ideal temperature for frozen food storage
-18 degree C (minus eighteen degree celsius)
Nutritional losses at different steps involved in freezing:
Peeling– Fruits and vegetables such as peaches, tomatoes or carrots are required to be peeled before freezing. This is not done by a manual process like at home and often involves use of hot water, hot sodium hydroxide solution or mechanical peelers. Nutritional losses occur as the peel contains several antioxidants and valuable fiber. Also, some carotene in the foods is lost due to oxidation as the peeled surface comes in contact with air.
Blanching– During blanching, hot water or steam is used to either facilitate peeling or stop enzyme activity. The water soluble vitamins such as folic acid, vitamin B12, vitamin C, biotin, etc are lost to some extent during the hot water treatment. While fruits are extremely sensitive to heat, mostly vegetables are blanched before freezing. Steam blanching is a better alternative to hot water blanching in order to preserve the water soluble nutrients.
Freezing -Freezing process has little effect on the nutritive value of the food but the blanching step itself is responsible for the major losses.
Frozen storage– Foods are known to remain well preserved at -18 degree C , but storage at higher temperatures and/or for long periods of time can cause vitamin losses and marked effects on color and flavor, which results in lower quality at the retail level. Vegetables that have been blanched have higher losses of vitamins C, B1 and B2 during frozen storage compared to unblanched.
We have , time and again, emphasized the importance of eating fresh, locally grown and seasonal fruits and vegetables and still stand by that ideology. The frozen fruits and vegetables cannot replace fresh ones in daily diet. But, their nutritive value is not very low and can be a part of healthy balanced diet once-in-a-while especially when you want to use peas for pulaos, corn for mexican salad, or strawberries for a smoothie.