In which food product is casein mainly found?

Casein is a type of protein that is primarily found in milk and dairy products. It constitutes about 80% of the protein content in cow's milk and is known for its ability to form a gel or curd when acidic conditions are present, such as when making cheese. This unique property makes casein particularly valuable in various culinary applications, including cheese-making and as a food additive in processed foods.

In contrast, meat contains different types of proteins, primarily muscle proteins, while vegetables and fruits are largely composed of carbohydrates, vitamins, and minerals, but contain negligible amounts of casein. Therefore, milk is the correct choice as it is the primary source of casein in the diet.