In fact, this principle is very simple, because the purple potato we often eat is very rich in anthocyanins. Anthocyanin is a water-soluble pigment. Lemon juice is squeezed into porridge. Lemon juice is acidic. When citric acid in lemon juice meets anthocyanin in purple potato, it will change the pH value of cell fluid, make it lower and acidic, so the color of purple potato porridge becomes red. This is a scientific experiment that students often study in class, and many students who have studied this kind of experiment will do it.
Because lemon juice is very acidic, it will change color when it meets many things. For example, lemon juice will change color when it meets iodophor. Squeeze lemon juice into iodophor solution, and the color of iodophor solution will fade. This is because lemon juice is rich in vitamin C, which has strong reducibility and can reduce the simple substance in iodophor to hydroiodic acid. Hydroiodic acid solution is colorless, so iodophor will fade when it meets lemon juice.
Lemon juice is also often used as a preservative for food, because citric acid in lemon juice can prevent other substances from oxidation. People eat fruits, such as apples and pears, which will turn brown when exposed to air, which is the reason for oxidation. Squeezing lemon juice on these fruits can prevent them from discoloring. So study is good. You won't know these interesting little scientific knowledge if you don't study. This knowledge is not only interesting, but also can be applied to daily life. Therefore, the school should lead children to do some small scientific experiments, so that children can find the fun of learning in the experiments.