Pheophytins a and

As pheophytin a and pheophytin b are the major degradation derivatives formed during extraction, food processing, and storage, some authors reconunend converting chlorophylls into the more stable pheophytins by treatment with HCl, ion exchange resin, or oxalic acid to estimate the chlorophyll contents. ... 

Homero-Mendez, D., Gandul-Rojas, B., and Mmguez-Mosquera, M.L, Routine and sensitive SPE-HPLC method for quantitative determination of pheophytin a and pyropheophytin a in olive oil. Food Int., 38, 1067, 2005. 

Zaprometov, M. N., N. V. Zagoskina and T. F. Koretskaya. Effect of some precursors on the formation of phenolic compounds in tea plant tissue cultures. Fiziol Rast 1976 23 1274. Higashi-Okai, K., S. Otani and Y. Okai. Potent suppressive activity of pheophytin A and B from the non-polyphenolic fraction of green tea (Camellia sinensis) against tumor promotion in mouse skin. Cancer Lett 1998 129(2) 223-228. 

Although the structures of the plant reaction centers are not yet known in detail, photosystem II reaction centers resemble reaction centers of purple bacteria in several ways. The amino acid sequences of their two major polypeptides are homologous to those of the two polypeptides that hold the pigments in the bacterial reaction center. Also, the reaction centers of photosystem II contain a nonheme iron atom and two molecules of plastoquinone, a quinone that is closely related to ubiquinone (see fig. 15.10), and they contain one or more molecules of pheophytin a and several... 

P680 is the primary electron donor, Ph is pheophytin-a and Q-Fe is a plastoquinone-iron complex. 

Porphyrins and their derivatives play critical roles in many biological functions. Some of the most remarkable examples are protoporphyrin IX and its iron complex that constitutes the heme prosthetic group, and the magnesium complexes of pheophytin a and bacteriopheophytin a that are known as chlorophyll a and bacteriochlorophyll a, respectively. These natural compounds are illustrated in Fig. 1 together with the structure of porphin,... 

Povoledo et al. (1975) also observed absorption bands at 410 and 670 nm for lake humic acids extracted without prior organic solvent extraction. They concluded that the pigments responsible for these bands were chlorophyll derivatives, notably pheophytin a, and reported the approximate content in humic acid from a Canadian lake sediment was 0. %. They reported that other pigments (e.g., carotenoids) were also present in lake humic acids without prior organic solvent extraction. Bourbonniere and Meyers (1978) extracted humic substances from Lake Huron surficial sediment without prior organic solvent extraction and measured visible spectra in 0.05N NaHC03 solution (pH 7.3-8.7) which gave 465/ 665 values of 3.92 for humic acid and 10.66 for fulvic acids. 

Table 1 is the compilation of pigment data obtained from analyses of the sediment trap samples. The data reveal, from the increase in the relative amounts of pheophytin-a and pheophor-bide-a, a large degree of Mg and Mg plus phytol loss, respectively. The deeper sample, upon microscopic examination, was found to contain a majority of broken, relative to intact, phytoplankton cells (diatom dominated) occurring mainly in fecal pellets. Thus, the change in the distribution of tetrapyrrole pigments, occurring with depth in the water column, reveals the combined effects of senescence/death and predation. The latter is evidenced by the increase in pheophorbide-a relative to pheophytin-a (37,40). 

The losses of magnesium and phytol through the combined effects of cellular senescence and predation (i.e. aerobic heterotrophy) in the water column lead to pheophytin-a and pheophorbide-a becoming the primary chlorophyll-a derivatives deposited in marine sedimentary environments. Though it is not known at present, the heterotrophic processes which cleave phytol more than likely also affect the 10-carbomethoxy group. Studies are underway to investigate the amounts of pyro-pheophorbides in water column detritus and surface sediments. 

Chlorophylls. Chlorophyll pigments are responsible for the greenish hues in virgin olive oil. Their content may range from 10 to 30 mg/kg. The main chlorophyll present in packed oil is pheophytin a. Chlorophyll a occurs in the oil just after production. Minguez-Mosquera and co-workers (1990) reported the presence of chlorophyll a, chlorophyll b, pheophytin a and pheophytin b in fresh oils. Psomiadou and Tsimidou (2001) found no chlorophyll a and only... 

The major pigments of rapeseed oil are the chlorophylls a and b, (Table 3.95). (Canola Council of Canada 1981 Niewiadomski etal., 1965) and their decomposition products pheophytin a and b. 

Table 1. (Bacterio)chlorophyll d i (Bacterio)pheophytin a and bacteriochlorophyll 663 in higher paints, cyanobacteria and photosynthetic bacteria.

Thirty-nine chlorophyll transformation products were separated on a C g colunw (. = 400nm) using a 40-min gradient from 90/10 methanol/water to 90/5/5 acetone/methanol/wato- [457]. Positive identification of methylated compounds within fiactions was made by thermospray MS. Pheophoibide a methyl ester, zeaxanthin, pyropheophorbide a methyl ester, isorenieratene, pheophytin a and b and pyiopheoph5 in a and b were confirmed. 

Chlorophyll a and b, pheophytin a and Z>, and -carotene from olive oil extracts were separated and quantitated on a silica column (A = 409 nm, 430 nm, or 452 nm) using a 98.5/1.5 hexane/IPA mobile phase. Detection limits of 0.5 ng total injected were reported and amounts from 0.1 to 45 pg/g were quantitated by this method [713]. 

Drexler and Ballschmiter [714] separated pheophytin a and b, chlorophyll a, a, and b, and xanthophyll in <10min using a diol coliunn (A = 425 nm) and a 100/2 hexane/ethanol mobile phase. In the same work, a description of the separation of... 

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. 

Table 3.28 shows that the composition of hydroperoxide isomers derived from an unsaturated acid by autoxidation ( 02) differs from that obtained in the reaction with 02- The isomers can be separated by analysis of hydroperoxides using high performance liquid chromatography and, thus, one can distinguish Type I from Type II photooxidation. Such studies have revealed that sensitizers, such as chlorophylls a and b, pheophytins a and b and riboflavin, present in food, promote the Type II oxidation of oleic and linoleic acids. 

Table 17.15. Chlorophylls a and b in vegetables and from the chlorophylls gives pheophytins a and b, fruit both of which are olive-brown. Replacing mag-...

Both chlorophylls contain a central magnesium ion in a chlorin chelate complex. Acid treatment removes the magnesium to give pheophytin a and b, which can be hydrolyzed yielding phytol and pheophorbide a and b (33 and 34), respectively ... 

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