Not all vegetables are suitable for eating raw. Some are best blanched in boiling water before consumption, while others must be thoroughly cooked. Four types of vegetables should not be eaten raw:
Wild vegetables like purslane
Wild vegetables like purslane need to be blanched to thoroughly remove dust and insects to prevent allergic reactions.
Cruciferous vegetables
Cruciferous vegetables such as broccoli and cauliflower are rich in nutrients. Blanching them improves their texture, and their abundant dietary fiber becomes easier to digest.
Mustard and similar vegetables
Mustard and similar vegetables, such as turnips, contain a substance called glucosinolate. When hydrolyzed, it produces volatile mustard oil, which aids in digestion and absorption.
Vegetables high in oxalic acid
Vegetables high in oxalic acid, such as spinach, bamboo shoots, and water bamboo, have oxalic acid that binds with calcium in the intestines to form calcium oxalate, which is difficult to absorb and interferes with the body's calcium absorption. Therefore, they must be blanched in boiling water before being served in a cold salad to remove most of the oxalic acid. Additionally, vegetables like lettuce and water chestnuts should be peeled, washed, and blanched before being eaten raw to ensure they are more hygienic without affecting their taste or nutritional content.
Of course, not all vegetables can be used in cold salads. Starchy vegetables like potatoes, taro, and Chinese yams must be cooked, as their starch granules will not break down, making them indigestible. Kidney beans contain large amounts of saponin and hemagglutinin; if not cooked thoroughly, they can cause food poisoning. Kidney beans should be cooked for a long time until they are fully cooked and their color changes before they can be safely eaten. Bean sprouts are best stir-fried, and even if used in a cold salad, they must be cooked first.