The appealing colours of fruit and vegetables are caused by pigments in the plant tissues that absorb light of certain wavelength. These pigments are caused by a large, structurally diverse group of compounds whose presence and relative concentrations vary with plant species, degree of ripeness, and growing conditions. They can be classified into two groups based on structure: compounds containing conjugated double bonds and compounds with metal-coordinated porphyrin rings (which also contain conjugated double bonds). Carotenoids and anthocyanins fall into the first group, while chlorophylls belong to the second.

 

Many natural plant pigments are available in purified, concentrated form for use as colour additives in the food industry. They are classified by the FDA as colours exempt from certification. Currently, 35 colours exempt from certification are approved as food colour additives, as shown in Table 1. Some of them, although naturally occurring, are available in synthetic form. In most cases, the synthetic form is chemically identical to the naturally occurring form and, therefore, is called “nature identical”. In general, naturally occurring colorants are more expensive and less stable than the synthetic FD&C colorants [1]. Thus many of the 26 colorants in this group are rarely used. For further information about the FDA Approved colours, please refer to the Code of Federal Regulations, Title 21, Food and Drugs, published by the Office of the Federal Register, USA [2].