Content heme pigments

The Hornsey (1956) procedure and its modifications have received widespread acceptance as relatively rapid measures of the adequacy of cure development in processed meats. The Hornsey procedure is also an accurate method for nutritional assessment of heme and heme iron content of meats (Carpenter and Clark, 1995), where ppm heme iron = ppm total heme/11.7. However, one caveat should be noted. The total heme pigment measurement is higher in cured meats than in similar uncured samples. Roasted turkey breast meat, for example, was reported by Ahn and Maurer (1989a) to have 23,26,34, and 34 ppm total pigment in samples formulated with 0, 1, 10, and 50 ppm nitrite, respectively. This effect should be considered to avoid overestimation of the heme iron content of cured meats. 

Total heme pigments vary among species and muscles, with levels >140 ppm for cooked beef products (Pearson and Tauber, 1984). Carpenter and Clark (1995) used the acetone extraction method of Hornsey (1956) to determine heme iron content of various cooked meats. They reported heme iron levels of 21,9, 2.2, and 1.4 ppm for cooked beef round, pork picnic, pork loin, and chicken breast, respectively. Hemin (mol. wt. 652) is 8.54% iron. Thus, these meats contained 245, 105,25, and 16 ppm total heme, respectively (Carpenter and Clark, 1995). Ahn andMaurer (1989a) reported a value of 23 ppm total heme in cooked turkey breast. 

The measurement of cured meat pigment concentration is based on the A540 of the nitrosyliron(II)protoporphyrin group (also known as nitrosylheme or NO-heme mol. wt. 646) in an extraction solution of 80% (final) acetone in water, taking into consideration the 70% water content of the meat sample. Hornsey (1956) established that only the pink NO-heme was extracted in 80% acetone. Heme groups from fresh meat pigments (Table F3.2.1) are not extractable in 80% acetone. However, upon acidification with hydrochloric acid, NO-heme in 80% acetone was completely oxidized to hemin. Thus, NO-heme concentrations could be expressed in equivalent ppm hemin. 

Hemosiderin, a mammalian non-heme iron storage protein with a similar function to ferritin. It contains iron oxyhy-droxide cores similar to those of ferritin, and it has been reported that these cores are present as large, dense, membrane-bound aggregates in vivo. It is assumed that hemosiderin is produced by lysosomal degradation of ferritin or possibly of ferritin polymers. Hemosiderin is deposited in the liver and spleen, especially in diseases such as pernicious anemia or hemochromatosis. The deposits are yellow to brown-red pigments. The iron content of hemosiderin is about 37%. Nonheme iron is also abundantly present in the brain in different forms. In the so-called high-molecular-weight complexes, iron is bound to hemosiderin and ferritin. The total amount of iron may differ in health and disease [F. A. Fischbach et al, J. Ultrastruct. Res. 1971, 37, 495 M. P. Weir, T. J. Peters, Biochem.J. 1984, 223, 31]. 

Further suggestive evidence that the carboxylated porphyrins are precursors of protoporphyrin is presented in the studies in C. diphtheriae. It had been shown by Pappenheimer that on low iron the production of porphyrin as well as of diphtheria toxin excreted into the medium was high when the iron content of the medium was increased, both the excretion of porphyrin and the toxin were diminished. Studying the heme and porphyrin pigments of this organism, Rawlinson and Hale observed that on a medium low in iron, the diphtheria bacillus excreted high concentrations of coproporphyrin III at the same time that heme production was diminished. When the iron content of the medium was increased to a level sufficient to inhibit toxin and coproporphyrin production, the intracellular heme components, namely, cytochrome a and b, but not c, rose five- to ten-fold. 

Soret region is dominated by the strong contributions of these pigments, as expected from the very low residual cyt c content (< 0.1 heme per reaction center). The only difference concerns the bound carotenoid, which visible absorption bands are blue-shifted by about 7 nm as compared to 15-15 cis-spheroidene in Rb. sphaeroides. In addition, oxidized reaction centers (in presence of ferricyanide) displayed a weak absorption band centered at 1245nm (not shown) attributed as in Rb. sphaeroides to a P+ transition. 

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