Table

Metalloproteins — Functionality and Color

Protein(s)

Hemoglobin, myoglobin Chlorophyll binding proteins Ceruloplasmin Haemovanadin

Metal (cofactor)

Fe Mg Cu V

Main Function

Transport of O2 and CO2 Photosynthesis Liver functionality O2 transport in ascidians

Color

Green

Blue

Apple-green

Source: Adapted from Hendry (1996).4

In the food industry, betalains are the most important pigments of the ^-heterocyclic group (Chapter 8). In addition, this subgroup of pigments has been related to melanins, which are the main pigments in hair and skin of mammals (Chapter 6). Purines and pterins are pigments of this group; they are important in fish and insects, whereas flavins (another member) are widely distributed (e.g., riboflavin is involved in redox biological processes) (Chapter 6). Interestingly, some marine invertebrates are pigmented by riboflavin; the same is true for several bacteria. Other ^-heterocyclic pigments, such as phenazines (bacterial pigments) and phenoxazines (present in bacterial and invertebrate organisms), are briefly discussed in Chapter 6.

The group metalloproteins comprises a large number of proteins that are widely distributed among living organisms because their biological function is essential for life (Table 3.1). These metalloproteins are not considered food additives, but chlorophyll has commercial importance (Chapter 9). However, the quality of some foods is related to coloration of metalloproteins (e.g., the red color of meat products). Another important aspect of metalloproteins is that some of them could be produced through biotechnology in sufficient quantity to be considered potential colorants in the future.5

However, and as pointed out above, the tremendous variability of organisms over the world means that a large group of miscellaneous pigments do not fit into this classification. In particular, it is common to find reports on the discovery of new pigments in bacteria, fungi, and invertebrates, whose structural characteristics are a clear reflection of their functionality and specificity in the host organism.4

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