Chlorophyll to pheophytin

The stability of olive oil compared with other vegetable oils is attributed to the high-to-low ratio of oleic to linoleic acid, and to the degradation of the chlorophylls to pheophytins (60). In addition, olive oil is also rich in antioxidative phenolic compounds such as hydroxytyrosol (66). 

Walker (1964) proposed that the ratio of chlorophyll to pheophytin could be used as a colour index for heated green vegetables. Reflectance measruements of... 

HAISMAN D R and Clarke M W (1975), The interfacial factor in the heat-induced conversion of chlorophyll to pheophytin in green leaves , J Sci Food Agric, 26, 1111-1126. 

A change in color occurs during storage of dried vegetables, its extent increases with increasing water content. The conversion of chlorophylls to pheophytins continues in blanched vegeta-... 

Studies of chlorophyll degradation in heated broccoli juices over the 80 to 120°C range revealed that chlorophylls degrade first to their respective pheophytins and then to other degradation products in what can therefore be described as a two-step process. Both chlorophyll and pheophytin conversions followed a first-order kinetics, but chlorophyll a was more heat sensitive and degraded at a rate approximately twice that of chlorophyll This feature had been observed by other authors. Temperature dependence of the degradation rate could adequately be described by the Arrhenius equation. ... 

In the past, no snitable analytical methodologies were capable of investigating these multiple reactions and even today, the complete extraction and analysis of all the componnds is still a difficult task. The methods for extraction must be optimized for each sample according to the solubility of either phytylated (chlorophylls and pheophytins) or dephytylated (chlorophyllides and pheophorbides) derivatives, often requiring several repeated steps and the use of a single or a mixture of organic solvents. 

Organized molecular assemblies containing redox chromophores show specific and useful photoresponses which cannot be achieved in randomly dispersed systems. Ideal examples of such highly functional molecular assemblies can be found in nature as photosynthesis and vision. Recently the very precise and elegant molecular arrangements of the reaction center of photosynthetic bacteria was revealed by the X-ray crystallography [1]. The first step, the photoinduced electron transfer from photoreaction center chlorophyll dimer (a special pair) to pheophytin (a chlorophyll monomer without... 

Figure 23-17 The zigzag scheme (Z scheme) for a two-quantum per electron photoreduction system of chloroplasts. Abbreviations are P680 and P700, reaction center chlorophylls Ph, pheophytin acceptor of electrons from PSII QA, Qg, quinones bound to reaction center proteins PQ, plastoquinone (mobile pool) Cyt, cytochromes PC, plastocyanin A0 and Aj, early electron acceptors for PSI, possibly chlorophyll and quinone, respectively Fx, Fe2S2 center bound to reaction center proteins FA, FB, Fe4S4 centers Fd, soluble ferredoxin and DCMU, dichlorophenyldimethylurea. Note that the positions of P682, P700, Ph, Qa/ Qb/ Ay and A, on the E° scale are uncertain. The E° values for P682 and P700 should be for the (chlorophyll / chlorophyll cation radical) pair in the reaction center environment. These may be lower than are shown.

It is important to note that chlorophylls are converted to pheophytins in the presence of acids (unit F4.t). Formation of a significant... 

Fig. 9 Reversed-phase chromatogram of frozen pea extract. The C, 8-column was subjected to an isocratic elution by acetone water (70 17 13). The chlorophylls and pheophytins were detected by fluorescence, with the excitation wavelength at 413 nm and the emission wavelength at 669 nm. (From Ref. 107.)...

---