"Health from Food" Series | Nutrients are lost after blanching vegetables, keep these key points in mind!

Vegetables are an important food in people's daily diet, containing various vitamins, cellulose and inorganic salts needed by the human body. In order to remove the peculiar smell and astringency of vegetables and maintain the color of vegetables, some vegetables need to be blanched when cooking. From a nutritional point of view, blanching will lead to the loss of water-soluble nutrients. When Chinese cabbage is blanched in 100℃ water for 2 minutes, the vitamin C loss rate is as high as 65%. If the heating time is too long, the vitamin C will be completely lost. In order to reduce the loss of nutrients, how should we blanch vegetables properly?

Blanching methods and operation points for common vegetables:

1. The small flower buds on the broccoli stems are densely packed together, making them very difficult to clean. Ordinary rinsing is not easy to remove insect eggs and pesticide residues, but blanching can effectively remove these pollutants. Note that the blanching time is about 2 minutes. To ensure the crisp taste of the broccoli, you can rinse it with cold water after blanching.

2. Green beans contain saponins and phytohemagglutinins, which can cause food poisoning if not cooked. Therefore, they must be blanched thoroughly in boiling water before eating to reduce the toxin content.

3. Spinach has a high oxalic acid content, which not only affects the taste, but also affects the absorption of minerals such as calcium, magnesium, and iron, and even causes urinary stones. Spinach can be blanched in boiling water for 30 to 60 seconds, which can remove most of the oxalic acid and maintain its taste and nutritional value.

4. Toona sinensis is almost harmless when fresh, but when left at room temperature for more than 3 days or in the refrigerator for more than 5 days, it will produce a large amount of nitrite, which can react with amines, the intermediate metabolites of proteins, to form carcinogenic nitrosamines. If Toona sinensis is handled properly, the risk of normal consumption is very low. Blanching before eating is one of the best ways to reduce nitrite. Blanching for 1 minute can remove more than 2/3 of nitrite and nitrate.

So what should we pay attention to during the blanching process?

1. Using boiling water and blanching for a short time can reduce the heat loss of nutrients.

2. Adding salt to water and placing the vegetables in a salt water solution can slow down the diffusion of soluble nutrients in the vegetables into the water.

3. The vegetables should be cooled down in time after blanching. The temperature of the vegetables after blanching is relatively high. After leaving the water, they will come into contact with the oxygen in the air and produce thermal oxygen, and the nutrients will continue to be lost. For this, the common method is to use cold water or cold air to cool down and dissipate heat.

4. Keep the vegetables intact as much as possible before blanching to reduce their contact area with water. If there are a lot of raw materials, add them in batches to ensure that the vegetables are in a higher water temperature.

The above are some precautions for blanching vegetables. In general, using some small methods during the blanching process of vegetables can effectively reduce the loss of nutrients.

Author: Han Lu, Henan University of Science and Technology

**Audit expert: ** Wang Yao, Associate Professor of the School of Food and Bioengineering, Henan University of Science and Technology