Yes, vegetables that are worried about pesticide residues need to be blanched.

For example, cauliflower, broccoli and other vegetables are not easy to clean, and there may be dust, parasites and pesticide residues.

Pesticides have high solubility in boiling water. Blanching water can remove some organophosphorus pesticides sprayed on vegetables, and boiling water can also kill pathogenic microorganisms and some parasites, so you can eat more safely.

In order to maintain the color of vegetables, or to remove off-flavor, astringency and oxalic acid, some vegetables must be blanched before cooking. But from a nutritional point of view, blanching will increase the loss of water-soluble nutrients. When Chinese cabbage was scalded in 100℃ water for two minutes, the loss rate of vitamin C was as high as 65%. After scalding for more than 10 minutes, vitamin C is almost lost. Therefore, appropriate methods should be adopted to minimize the loss of nutrients.

Using boiled water with large amount of water and short blanching time can reduce the heat loss of nutrients. Because there is oxidase in plant cells, it can accelerate the oxidation of vitamin C, especially at the water temperature of 60℃ ~ 80℃. In boiling water, oxidase is unstable to heat and soon loses its activity. At the same time, there is almost no oxygen in boiling water, which reduces the loss of vitamin C caused by thermal oxidation.

Adding 1% salt to blanching water can make vegetables in physiological salt solution and slow down the diffusion of soluble nutrients in vegetables into water.

Try to keep the vegetables intact before blanching and reduce the contact area between heat and water. In the case of more raw materials, it is necessary to feed them in batches to ensure that the raw materials are at a higher water temperature.

After blanching, the temperature of vegetables is relatively high, and after leaving water, they contact with oxygen in the air to produce hot oxygen, which is the continuation of nutrient loss. Therefore, vegetables after blanching should be cooled in time. The common method is to use a lot of cold water or cold air to cool down and dissipate heat. The former, because vegetables are put in water, soluble nutrients are lost due to the action of water; The latter is better because there is no such factor.

According to the analysis, the average preservation rate of vitamin C in blanched vegetables is 84.7%.