Advances in studies on carotenoids in Malus pumila

Carotenoids are important components responsible for the coloration of apples, with both the composition and content of carotenoids deciding fruit appearance and nutritional value. We reviewed the recent advances in the study of carotenoids in apples, including carotenoid content and composition, changes during fruit development and storage, genes and enzymes involved in the carotenoid biosynthetic pathway, and the relationship between environmental factors and accumulation of carotenoids. The regulatory mechanism of the carotenoid biosynthesis pathway in the apple remains to be further studied.