As a new type of sanitary product, plastic wrap is increasingly used in homes. While it plays a role in preventing the mingling of flavors and maintaining the freshness of various dishes in the refrigerator, does it actually protect the nutritional content of the food?
Relevant personnel conducted the following experiment: Fresh vegetables such as tomatoes, winter melon, chili peppers, cucumbers, yellow chives, and lettuce were washed, cut using ordinary household methods, and air-dried. They were then stir-fried in a wok and divided equally into two bowls. One bowl was covered with plastic wrap, while the other was not. Both were placed in the refrigerator simultaneously. After 6 hours and 24 hours, respectively, they were taken out to measure their vitamin C content, and the results were quite interesting.
Covering dishes with plastic wrap while they are hot and not yet cooled: In dishes without plastic wrap, the preservation rate of vitamin C was 85%, whereas in covered dishes, it was 71%. It appears that covering hot dishes with plastic wrap not only fails to preserve the vitamin C in vegetables but actually increases its loss. Therefore, one should not cover freshly cooked dishes immediately with plastic wrap. To protect vitamin C, the vegetables must be completely cooled before covering them with plastic wrap.
Covering cooled dishes with plastic wrap: After 6 hours in the refrigerator, the covered and uncovered vegetables were compared. For example, 100 grams of uncovered tomatoes contained 19 mg of vitamin C, while covered tomatoes contained 22 mg. Winter melon contained 25 mg and 30 mg of vitamin C, respectively. White radish contained 25 mg and 27 mg, respectively. The preservation effect of plastic wrap on green peppers is more significant. 100 grams of uncovered green peppers contained 59 mg of vitamin C, while covered ones contained 66 mg, equivalent to the vitamin C in one large peach. Therefore, covering dishes with plastic wrap in a timely manner after cooking can effectively protect their nutritional content.
After more than a day, the effectiveness of plastic wrap varies by vegetable: When the experiment was extended to 24 hours, the results differed from those at the 6-hour mark. At this point, the protective effect of plastic wrap on vitamin C cannot be generalized and depends on the specific vegetable. For instance, 100 grams of covered yellow chives contained 1.33 mg more vitamin C than uncovered ones, and lettuce leaves contained 1.92 mg more, similar to the 6-hour results. However, some vegetables showed drastically different results. For example, after 24 hours of storage, 100 grams of covered sword beans lost 1.5 mg of vitamin C, and radishes lost 3.4 mg. Even more significantly, 100 grams of cucumbers lost 3.8 mg. This means that a bowl of covered cucumbers left in the refrigerator for a day and a night loses an amount of vitamin C equivalent to that in five apples.
As is well known, vitamin C is a nutrient that the human body cannot synthesize on its own and must obtain from external sources. Its required quantity is the largest among all vitamins. Vegetables and fruits are a major source of vitamin C for the human body, and the intake of vitamin C from vegetables in three daily meals is particularly important. Therefore, reducing the loss of vitamin C in vegetables can effectively ensure the body's daily normal intake of this vitamin. The correct and rational use of plastic wrap can achieve事半功倍 (twice the result with half the effort).