Exogenous substances in food, including food additives and pollutants, generally account for a small proportion in food. However, they have a great influence on food. In a proper proportion, food additives and pollutants often show opposite effects.

Endogenous substances are divided into two categories, 15, which is the main content of food composition. Among them, inorganic components include water and inorganic components, and organic components include protein and amino acids, carbohydrates (including cellulose), lipids, vitamins, nucleic acids, enzymes, hormones, ethanol, alkaloids, pigment components, aroma components, taste components and toxic components, with a total of 13.

The above division of food ingredients is not based on the consideration of chemical composition and properties of substances. Like inorganic substances, vitamins, pigments, etc. Their specific substances, components and properties are not much. The reason for this distinction is to classify ingredients with the same or similar functions into one category from the perspective of food and nutrition, so as to facilitate the development and discussion of the whole content.

According to the content of food ingredients, food ingredients can also be roughly divided into six kinds, namely: water, protein, fat, carbohydrate (without cellulose), cellulose (commonly known as fiber) and inorganic substances. This is the general ingredient in 6, while vitamins, hormones and so on. It's all trace components. The total content of general ingredients in food is basically 100% of the total content of food ingredients. But for special foods, such as liquor, this relationship does not exist.

Composition difference

Only some of the ingredients in various foods are the same. And the content of these ingredients in each food is also very different. Therefore, food is a combination of one or more or various food ingredients, and it is a mixture. In other words, all kinds of food can be composed of food ingredients, which is the composability of food ingredients. It is precisely because of the combination that the internal differences of various foods are created, which leads to our evaluation of the nutritional value of food.