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flour is wheat flour, and starch is potato or sweet potato flour. It can’t be exchanged. For example, to make steamed bread, it must be flour, but starch can’t. But you can also use flour to make soup, but the effect is not good
starch is pure starch, while flour is ground from wheat. It contains not only starch, but also protein, minerals, etc.
the main component of flour is starch, about 70-90%, and the rest is protein, a small amount of fat and non starch sugars. Starch is a high polymer with a lot of glucose.