Heme pigments

Bacterial pigments. Some bacteria commonly found in caries lesions are known to produce pigments. For example, the black staining of plaque is related with Actinomyces (Slots, 1974), but its chemical nature remains unknown. Black pigmented Prevotella produces both iron sulphide and heme pigments (Shah et ah, 1979). In addition, Propionibacterium forms porphyrins (Lee et al., 1978). Bacterial iron-binding peptides, which can contribute to discoloration, increase in the saliva of subjects with a high caries frequency (Nordh, 1969). 

Some studies indicate that nitrite or related compounds have antioxidant activity even in systems that do not contain heme pigments. MacDonald et al. 

Igene, J. O., King, J. A., Pearson, A. M., and Gray, J. 1. (1979). Influence of heme pigments, nitrite, and non-heme iron on the development of warmed-over flavor (WOF) in cooked meat. J. Agric. Food Chem. 27, 838-842. 

Hornsey (1956) also found that extraction with an acidified 80% acetone solution for 1 hr gave a hemin solution, derived from oxidation of the heme moiety of both NO-heme and non-nitrosylated heme pigments. Hemin absorption spectra exhibited distinct peaks at 512 and 640 nm. Hornsey (1956) used the A640 of sample filtrates as a measure of the total heme pigments. Solutions of both hemin and NO-heme in 80% acetone conformed with Beer s... 

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. 

About 80% to 90% conversion of heme pigments to nitrosylhemochrome is desirable for cured meats (Pearson and Tauber, 1984). However, beef pastrami with typical cured color may have as low as 62% conversion (94 ppm NO-heme out of 153 ppm total heme Cornforth et al., 1998). 

This paper provides the basic information for spec-trophotometric determination of nitrosyl and total heme pigment levels in cured meats. 

This paper is an adaptation of the Hornsey (1956) method for measurement of nitrosyl and total heme pigments in cured meats, using 2 g meat samples rather than 10 g samples. Thus, less reagent is needed and more samples may be analyzed at the same time. 

A subsequent study (J 5) using the model meat system showed that removal of the heme pigments or addition of 156 ppm of nitrite significantly inhibited lipid oxidation in cooked meat, which supports the earlier concept that myoglobin (Mb) is involved in WOF. However, it should be borne in mind that removal of heme pigments by leaching will also remove a number... 

It is interesting to also note that treatment with H2O2 destroys even more of the heme pigments than heating, resulting in still greater oxidation of the meat system (Table III). On the other hand, addition of 2% EDTA markedly reduced autoxidation as shown by much lower TBA numbers. 

Jj>)> it seems more probable that nitrite stabilizes the heme pigments so that they do not release Fe + and thus catalyze development of WOF. The inhibition of WOF by EDTA lends further credence to this theory, which as yet is unproven. 

The use of model meat systems has been shown to be helpful in elucidating the role of different compounds in development of WOF. Results of these studies have shown that the major catalyst of WOF is Fe2+, which is released from the heme pigments by heating, and presumably by grinding. The phospholipids are the major lipids involved in development of WOF, in contrast to oxidation during frozen storage, where the... 

D4. Day, R., Kernicterus Further observations on the toxicity of heme pigments. Pediatrics 17, 925-928 (1956). 

The basic structure of the heme pigments consists of four pyrrole units joined together into a porphyrin ring as shown in Figure 6-11. 

The reactions of the heme pigments in meat and meat products have been summarized in the scheme presented in Figure 6-13 (Fox 1966). Bilin-type structures are formed when the porphyrin ring system is broken. 

Arsine poisoning can lead to acute renal tubular necrosis and ultimately to oliguric/anuric renal failure (Rogge et al, 1983). Renal failure can be attributed to (1) direct effect of arsine on renal tissue, (2) heme-pigment nephropathy, or... 

The mechanism of the acute kidney injury is thought to be multifactorial and similar to other cases of myoglobinuric renal failure [118, 121-126]. These factors include obstruction of tubules, toxic effects of the pigment or iron on renal tubular cells and altered hemodynamics in association with inhibition of the vasodilator nitric oxide by myoglobin. Experimental animals exposed to heme pigment have increases in the renal synthesis of both heme oxidase and ferritin [125]. This allows for more rapid heme degradation and greater sequestration of potentially toxic iron by the tubular cells [125]. Whether narcotics or the hypotensive, hypoxic environment associated with rhabdomyolysis interfere with these protective effects of the kidney is unknown. 

Meat proteins include sarcoplasmic, myofibrillar, and connective tissue proteins. Among the sarcoplasmic proteins are heme pigments and enzymes, which influence the color, smell, and structure of meat. Myofibrillar proteins and collagen are able to retain and hold water in meat structure and to emulsify fat. Therefore they influence the rheological properties of meat products. 

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