Heme is actually originated from the Greek word for blood and is responsible for the red color of two important pigments in animal species: hemoglobin, existing in the blood, and myoglobin that resides in the muscular tissues (Table 6.2). Basically, myoglobin gives the red color to meat and during processing, this pigment is subjected to chemical and color changes, for instance freshly cut meat renders a purplish color (Delgado-Vargas et al., 2000; Suman & Joseph, 2013). Upon exposure to air, a delightful red hue is observable at the surface of the meat according to the oxygenation of myoglobin (an oxygen molecule is bound to the heme compound akin to the oxygenation process of hemoglobin).
Several types of chlorophylls have been mentioned in the literature. Accordingly, chlorophyll a plus chlorophyll b are among two commonly used colorants in food processing because they are abundant agents in green plant tissues and are available at the relative ratio of 3:1. Tetrapyrrole derivatives are the core components of these natural colorants and in this view, they resemble heme pigments. In contrast to the heme group that contains iron as the central atom, magnesium is located at the central part in chlorophylls. Also, the pyrrole unit IV exists in the hydrogenated form within chlorophylls. Another feature of chlorophylls is their water-insoluble 20-carbon phytyl group, as shown in Table 6.2 (Delgado-Vargas et al., 2000; Delgado-Vargas & Paredes-Lopez, 2002). Most of the leafy (lettuce, broccoli, cabbage etc.) and nonleafy (gilki, peas, asparagus, etc.) vegetables as well as unripe fruits are green owing to the chlorophyll pigment. Chlorophyll is relatively a labile molecule, but its stability can be increased by de-esterifying the chlorophyll and via the addition of copper ions. These copper complexes have a satisfactory green color and are more stable compared with its intact counterpart. In addition, the bright green chlorophylls can change to olive brown pheophytins by replacing the magnesium of the molecule with hydrogen.