Pigments in cured meats

Both nicotinic acid and nicotinamide have been used in the enrichment of bread, flour, and other grain-derived products. Animal feed is routinely supplemented with nicotinic acid and nicotinamide. Nicotinamide is also used in multivitamin preparations. Nicotinic acid is rarely used in this appHcation. The amide and carboxyHc acid have been used as a hrightener in electroplating baths and as stabili2er for pigmentation 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. 

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. 

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

Skibsted and Bohle afforded kinetic and mechanistic studies on the autoxidation process of MbnNO, the pigment found in cured meat, whose products are Mbm and N03 .97 A detailed revision of this reaction was performed by using spectrophoto-metric measurements with singular value decomposition and global analysis of the absorption spectra.97c Two consecutive pseudo-first-order reactions were detected, with /v0 )s values of about 10 4s 1 at 20°C, indicating the growth and decay of a reaction intermediate, as in reaction 7.33 ... 

Greenwood, D. A., Lewis, W. L., Urbain, W. M., and Jensen, L. B. 1940. The heme pigments of cured meats. IV. Role of sugars in color of cured meats. Food Research 6, 625. 

In meat curing, nitrite is traditionally used for developing the pink, heat-stable pigment. Its other important role is the inhibition of the outgrowth of Clostridium botulinum spores in pasteurized products and, in some countries, in several types of smoked fish. Nitrite also serves as an antioxidant and contributes positively to the development of the flavor of cured-meat. The undesirable side-effect, however, is the reaction of nitrite with amino groups of food constituents, leading to the formation of NNCs. 

In canned meats, ascorbate also enhanced NOMb production (Reith and Szakaly, 1967b). Without ascorbate, a Mb nitrite molar ratio of 1 5 was needed for optimum formation of NOMb. With ascorbate, a ratio of 1 Mb 3 nitrite was sufficient for maximum NOMb formation. Sodium erythorbate was equivalent to sodium ascorbate for NOMb formation. Canned meats formulated with potassium nitrate showed no formation of cured meat pigment. 

Killday etal. (1988) also provided evidence for internal autoreduction of ferric nitrosyl heme complexes, as previously proposed by Giddings (1977). Heating of chlorohemin( iron-III) dimethyl ester in dimethyl sulfoxide solution with imidazole and NO produced a product with an infrared spectra identical to that of nitrosyl iron(ll) protoporphyrin dimethyl ester prepared by dithionite reduction. Both spectra clearly showed the characteristic nitrosyl stretch at 1663 and 1665 cm. They thus proposed a mechanism for formation of cured meat pigment which includes internal autoreduction of NOMMb via globin imidazole residues. A second mole of nitrite is proposed to bind to the heat-denatured protein, possibly at a charged histidine residue generated in the previous autoreduction step. 

Cured meat pigment (nitrosyl ferrohemochrome) may be prepared by gaseous NO treatment of hemin (Shahidi etal., 1985). O Boyle etal. (1990) used cured meat pigment produced by this method in the production of nitrite-free weiners, lowering the possibility for nitrosamine formation in these products during heat processing. This process also has not yet been incorporated into commercial practice. 

Color and color uniformity are important criteria for retail acceptance of both fresh and processed meats. This unit describes the methods for detection and quantitation of pigments in nitrite-cured or uncured cooked meats. Protocols for measurement of fresh meat pigments are presented in UN1TF3.3. 

The pink cured meat pigment mononitrosylhemochrome is a complex of nitric oxide (NO), ferrous heme iron, and heat-denatured globin protein (Table F3.2.1). The pink nitrosylheme (NO-heme) moiety may be extracted from the protein in aqueous acetone and quantitated by A540 (see Basic Protocol 1). The percent nitrosylation may be determined from measurement of ppm NO-heme relative to ppm total acid hematin (hemin) extracted in acidified acetone (see Basic Protocol 2), since NO-heme is completely oxidized to hemin in acid solution (i.e., 1 ppm NO-heme = 1 ppm hemin). 

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. 

Sebranek (1988) has reviewed the effects of heat on denaturation of the proteins. Dehydration by heat denatures the muscle proteins, particularly the sarcoplasmic proteins. This induces a rather dramatic change in meat color. The heme pigments, which provide most of the color of fresh meat, serve as a general indication of doneness or temperature history. In the case of cured products, heme pigments react to form nitric oxide hemochro-mogen, which contributes the characteristic pink cured meat color (Pearson and Tauber, 1984). 

Pig. 3. Derivatives of myoglobin of importance in meats. In the outer circle are represented the insoluble hemochromogens obtained by coagulation. Only in the case of the cured meat pigment is the denatured compound red. Dotted portions represent possible intermediates between metmyoglobin and the cured meat pigment. 

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