Color, pigments pheophytins

The chlorophyll pigments are not stable to heat. The green color disappeared after the canning process largely due to the breakdown of chlorophylls into pheophytins. This was also evidenced by the large change in a value from -8.1 to +0.3 (see Table VIII). 

Nuclear magnetic resonance spectroscopy (NMRS) has also been used to detect adulteration in olive oil (Mannina et al., 2003). To improve the color of virgin olive oil, chlorophyll molecules are sometimes added. This addition may be detected by NMRS because chlorophyll and pheophytin, the regular tetrapyrrole pigments of olive oil, give a different spectrum. 

Roy et al. (1991) extracted the pigments of green leafy vegetables in methanol-acetone-diethyl ether (1 1 1) the extracts were evaporated, reconstituted in the same solvent, and separated by TLC on silica gel G plates with a chloroform-petroleum ether-toluene-acetone (5 4 4 3) mobile phase. Pheophorbide b, mixed carotenoid, pheophorbide a, chlorophyll b, pheophytin b, chlorophyll a, pheophytin a, and carotene bands were obtained. This method can be used to detect artificial and natural colorants in food products. 

The chromatogram obtained on separating pheophytins a and b from their respective Cu and Zn complexes (Figure 7.19) [27] enables detection of a possible alteration or adulteration of food color. As can be deduced from the retention times of these complexes, their separation from the rest of the pigments is perfectly practicable. 

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