8 food biochemistry and food phần 67

P1: SFK/UKS BLBS102-c17 P2: SFK BLBS102-Simpson March 21, 2012 11:52 Trim: 276mm X 219mm Printer Name: Yet to Come 17 Chemical and Biochemical Aspects of Color in Muscle-Based Foods it is rapidly oxidized between pH and 7, releasing the different parts of the Mb (globin, iron, and the tetrapyrrole ring) From a chemical point of view, it should be borne in mind that the color of Mb, and therefore of the meat or meat products, not only depends on the molecule that occupies the sixth coordination site, but also the oxidation state of the iron atom (ferrous or ferric), the type of bond formed between the ligand and the heme group (coordinated covalent, ionic, or none) and the state of the protein (native or denaturalized form), not to mention the state of the porphyrin of the heme group (intact, substituted or degraded) (P´erez-Alvarez 1996) During heat treatment of fish flesh, aggregation of denatured fish proteins is generally accompanied by changes in light scattering intensity Results demonstrate the use of changes in relative light scattering intensity for studying structural unfolding and aggregation of proteins under thermal denaturation (Saksit et al 1998) When fatty fish meat like Trachurus japonicus was heat treated, MMb content increased linearly, and the percentages of denatured Mb and apomyoglobin increased rapidly when mince was exposed to heat, but when temperature reach 60◦ C, the linearity is broken Results indicated that stability of the color was higher than that of Mb and that the thermal stability of heme was higher than that of apomyoglobin (Hui et al 1998) Both Mb and ferrous iron accelerated lipid oxidation of cooked water-extracted fish meat EDTA inhibited the lipid oxidation accelerated by ferrous iron, but not that accelerated by Mb Also, with cooked nonextracted mackerel meat, EDTA noticeably inhibited lipid oxidation Nonheme iron-catalysis seemed to be related in part to lipid oxidation in cooked mackerel meat Addition of nitrite in combination with ascorbate resulted in a marked inhibition of lipid oxidation in the cooked mackerel meat From these results, it was postulated that nitric oxide ferrohemochromogen, formed from added nitrite and Mb, present in the mackerel meat in the presence of a reducing agent, possesses an antioxidant activity, which is attributable in part to the function as a metal chelator (Ohshima et al 1988) Tuna fish meat can be improved in its color when the flesh is treated with CO The specific spectrum of carboxymyoglobin (COMb) within the visible range can be obtained Penetration of CO into tuna muscle was very slow After approximately 1–4 hours CO had penetrated 2–4 mm under the surface, and after hours, CO had penetrated 4–6 mm Mb extracts from tuna muscle treated with CO exhibited higher absorbance at 570 than at 580 nm (Chau et al 1997) Jayasingh et al (2001) reported that CO (0.5%) can penetrate to a depth of 15 mm (1 week) in ground beef These authors also mentioned that when COMb is exposed to atmospheres free of CO, COMb slowly dissociate from Mb In dry-cured meat products, as Parma ham (produced without nitrite or nitrate), the characteristic bright red color (Wakamatsu et al 2004a) is caused by Zn-protoporphyrin IX (ZPP) complex, a heme derivative This type of pigment can be formed by endogenous enzymes as well as microorganisms (Wakamatsu et al 2004b) Spectroscopic studies of Parma ham during processing all process, revealed a gradual transformation of muscle Mb, initiated by salting and continuing during aging Pigments became increasingly lipophilic during processing, suggesting that 321 a combination of drying and maturing yields a stable red color (Parolari et al 2003) Electron spin resonance spectra showed that the pigment in dry-cured Parma ham is at no stage a nitrosyl complex of ferrous Mb as found in brine-cured ham and Spanish Serrano hams (Moller et al 2003) These authors also establish that heme moiety is present in the acetone/water extract and that Parma ham pigment is gradually transformed from an Mb derivative into a nonprotein heme complex, thermally stable in acetone/water solution Adamsen et al (2003) also demonstrated that the heme moieties of Parma ham pigments have also antioxidative properties COLOR CHARACTERISTICS OF BLOOD PIGMENTS Hb has function carrying oxygen to the tissues Thus, the oxygenated hemoglobin Hb(Fe(II))O2 is a very stable molecule but does slowly auto-oxidize at a rate of about 3% per day This rate is accelerated at lower oxygen tensions if the Hb is partially oxygenated The “blood pigments” chemistry is actually quite complex (Umbreit 2007) Nagababu and Rifkind (2000) reported that the autooxygenation generates Hb(Fe(III)), called methemoglobin (MHb), and superoxide At least in vitro, the superoxide undergoes dismutation to hydrogen peroxide and oxygen The hydrogen peroxide is rapidly decomposed by catalase The sixth coordinate of the MHb is occupied with water If not immediately destroyed, the hydrogen peroxide would react with Hb(Fe(II))O2 to produce ferrylhemoglobin, Hb(Fe(IV)) = O, with a rhombic heme that reacts with further hydrogen peroxide to produce free Fe(III) and porphyrin degradation products Jaffe (1981) reported that the MHb can be reduced by the NADH-cytochrome b5-MHb reductase or by direct reduction by ascorbate and glutathione The Hb can react with nitrites; the reaction with oxyhemoglobin (OHb) limits the half-life of the NO The reaction with free Hb is so fast that any NO is consumed immediately (Vaughin et al 2000, Huanf et al 2001) According to Umbreit (2007), there are two major reactions of the nitrogenous compounds with Hb Fe(II), one binding NO to the heme and the other reducing nitrite to NO Muscles can retain several amounts of blood Thus, Richard et al (2005) reported that dark muscle from Atlantic mackerel contained roughly equal amounts of Hb and Mb, although in other fish species such as bluefin tuna (T thynnus) Hb can be the major heme compound in dark muscle “sangacho” (S´anchezZapata et al 2009a) Niewiarowicz et al (1986) reported that in different poultry dark meat species the ratio between Hb and Mb varies from 20% to 40% In mammals, this ratio has been reported to range from 7% to 35% (Han et al 1994) Animal blood is little used in the food industry, because of dark color it imparts to the products to which it is added Attempts to solve food color related problems have employed several different processes and means, but they are not always completely satisfactory The addition of 12% blood plasma to meat sausages lead to pale-colored products Another means of solving color problems is the addition of discolored whole blood or globin by P1: SFK/UKS BLBS102-c17 P2: SFK BLBS102-Simpson 322 March 21, 2012 11:52 Trim: 276mm X 219mm Printer Name: Yet to Come Part 3: Meat, Poultry and Seafoods eliminating Hb’s heme group From blood, natural red pigments can be obtained without using coloring agents such as nitrous acid salts; these pigments have zinc protoporphyrin as the metalloporphyrin moiety, and can be used in producing beef products, whale meat products, and fish products (including fish pastes), and a favorable color (Numata and Wakamatsu 2003) There was wide variation in amounts of Hb extracted from muscle tissue of bled and unbled fish, and the residual level in the muscle of bled fish was substantial Mb content was minimal as compared to Hb content in mackerel light muscle and trout whole muscle Hb made up 65% and 56% of the total heme protein by weight in dark muscle from unbled and bled mackerel That blood-mediated lipid oxidation in fish muscle depends on various factors, including Hb concentration, Hb type, plasma volume, and erythrocyte integrity (Richards and Hultin 2002) Alvarado et al (2007) reported that the Hb content can vary a lot among animal species and muscle types; it is clear that the Hb levels present in muscle-based foods have the potential to substantially contribute to lipid oxidation Also, the presence of blood, Mb, Fe2+ , Fe3+ , or Cu2+ can stimulate lipid oxidation in the fillets of ice-fish (Rehbein and Orlick 1990) The formation of ferryl and/or perferryl species upon reaction with hydrogen peroxide or lipid hydroperoxides has been reported to be either truly initiators or important catalysts of lipid oxidation in raw muscle meat products (Baron and Andersen 2002) Various factors such as the ability of the Hb to auto-oxidize and release of hematin, the heme–iron moiety nonbound to the protein, have also been reported to be crucial in promoting lipid oxidation (Grunwald and Richards 2006) As was mentioned in the preceding text, blood utilization by the food industry is minimal, but many blood sausages are elaborated around the world (Diez et al 2009) Problem associated with blood uses is discoloration through the disruption of the heme group of the Hb moiety Several attempts are made to find a possible solution to the color problems caused by blood addition, one of them is the Hb moiety conversion into the more stable and sensorial accepted carboxyhaemoglobin (COHb) by saturation with carbon monoxide (CO) This pigment is very stable and can be visualized by the reflectance spectra (400–700 nm) (Fontes et al 2010) Fontes et al (2010) reported differences between the spectra of blood CO-treated and its untreated counterpart When CO was bubbled into the blood samples, the spectra reflected the COHb color properties in the red region, whose maximum reflectance occurs at 700 nm Greater color stability was also observed in CO-treated sample as indicated by small differences between reflectance curves In adipose tissues, residual Hb is associated with the presence of capillaries or with hemorrhage Irie (2001) reported that internal fat is whiter, with less Hb and with harder fat, than subcutaneous fat The Hb derivatives are MHb, OHb, and deoxyhemoglobin (DHb) This Hb derivatives show different reflectance and absorbance spectra in which each showed different absorbance bands (AB); thus, MHb showed AB at 406, 500, and 630 nm; OHb showed 418, 540–542, 516–578, 950 nm; and DHb showed 430, 555, 760, and 910 nm From technological point of view, COMb can be used in several types of meat processing; thus, CO can be used in (i) modified atmosphere packaging of several type of meats (Raines and Hunt 2010), (ii) pasteurized meat products (Fontes et al 2004), (iii) dry blood (Fontes et al 2010), and (iv) combination with injection-enhancement ingredient (lactate) for beef color stabilization (Suman et al 2010) But several legal problems are associated with its use; thus, the industry must avoid its use to rejuvenate the color of spoiled meat Stiebing (1990) reported that during cooking, the oxygen partial pressure in blood sausages decreases to a point where oxidation occurs, instead of oxygenation But the CO-treated blood can increase shelf life (refrigerated storage, days) FAT COLOR From a technological point of view, fat fulfils several functions, although as regards color, its principal role is in the brightness of meat products Processes such as “afinado” during the elaboration of dry-cured ham involve temperatures at which fat melts, so that it infiltrates the muscle mass and increases the brilliance (Sayas 1997) When the fat is finely chopped, it “dilutes” the red components of the color, thus decreasing the color intensity of the finished product (P´erez-Alvarez et al 2000) However, fats not play such an important role in fine pastes because, after emulsification, the fat is masked by the matrix effect of the emulsion, so that it contributes very little to the final color The color of fat basically depends on the feed that the live animal received (Esteve 1994, Irie 2001) In the case of chicken and ostrich, the fat has a “white” appearance (common in Europe) when the animal has been fed with “white” cereals or other ingredients not containing xanthophylls, since these are accumulated in subcutaneous fat and other fatty deposits However, when the same species are fed on maize (rich in xanthophylls), the fatty deposits take on a yellow color Beef or veal fat that is dark, hard (or soft), excessively bright or shiny lowers the carcass and cut price Fat with a yellowish color in healthy animals reflects a diet containing beta-carotene (Swatland 1988) While fat color evaluation has traditionally been a subjective process, modern methods include such techniques as optical fiber spectrophotometry (Irie 2001) Another factor influencing fat color is the concentration of the Hb retained in the capillaries of the adipose tissues (Swatland 1995) As in meat, the different states of Hb may influence the color of the meat cut OMb is responsible for the yellowish appearance of fat, since it affects different color components (yellow-blue and red-green) The different states of Hb present in adipose tissue may react in a similar way as in meat, so that fat color should be measured as soon as possible to avoid possible color alterations When the Hb in the adipose tissue reacts with the nitrite incorporated in the form of salt, nitrosohemoglobin (NOHb) is generated, a pigment that imparts a pink color to the fat This phenomenon occurs principally in dry-cured meat products with a degree of anatomical integrity, such as dry-cured ham or shoulder (Sayas 1997) P1: SFK/UKS BLBS102-c17 P2: SFK BLBS102-Simpson March 21, 2012 11:52 Trim: 276mm X 219mm Printer Name: Yet to Come 17 Chemical and Biochemical Aspects of Color in Muscle-Based Foods When fat color is measured, its composition should be kept in mind, since its relation with fatty acids modifies its characteristics, making it more brilliant or duller in appearance The fat content of the conjunctive tissue must also be borne in mind, since collagen may present a glassy appearance because, at acidic pH, it is “swollen”, imparting a transparent aspect to the product REDUCED NITRITE MEAT PRODUCTS Health concerns relating to the use of nitrates and nitrites in cured meats (cooked and dry cured) have led to a tendency toward decreased usage to alleviate the potential risk of the formation of carcinogenic, teratogenic, mutagenic N-nitroso compounds (Karolyi 2003), cytotoxic effects of nitrosamines and by the toxic effects of nitrite per se (metmyoglobinaemia and fall of blood pressure) But it is well known that nitrate/nitrite is widely used as a curing agent in the meat industry, although in recent years its omission from meat processing has been proposed (ViudaMartos et al 2009a) Meat scientists have to take into account that any technological strategy (P´erez-Alvarez 2008) or the use of other ingredients (meat, nonmeat, and functional ingredients) can modify color characteristics (P´erez-Alvarez and Fern´andez-L´opez 2009a, S´anchez-Zapata et al 2009b) As soon as nitrite is added in the meat formulation, it starts to disappear (nitrite is reduced to nitric oxide (NO)) that reacts with Mb to form NO-OMb and often can no longer be detected analytically at a later time The rate of depletion is dependent on various factors, such as pH, initial nitrite concentration, processing and storage temperatures, meat-to-water ratio, and the presence of reductants (P´erez-Alvarez et al 1993) According to P´erez-Alvarez (2006), two-thirds of the Mb present in the meat is transformed into NOMb, although it is possible that only 50% of the Mb reacts The rest corresponds to the residual nitrite Residual nitrite levels (10–20% of the originally added sodium nitrite) correspond to nitrite that has not reacted with Mb and it is available for other reactions in the organism (Fern´andez-L´opez et al 2007) Recently, it has been found that plants and their extracts can be used as indirect sources of nitrate (Shahid-Umar and Iqbal 2007, Shahid-Umar et al 2007, Parks et al 2008) in the production of meat products (Sebranek and Bacus 2007a, 2007b) Six “technological” pathways exist for reducing the nitrite present in the meat products: Exposure to γ radiation, as described by Wei et al (2009) Reaction with compounds of a polyphenolic nature (Garrote et al 2004) derived basically from spices added in the formulation of the meat products Also, can react with polyphenols, mainly hydroxycinnamic acids, like caffeic or ferulic acid, or with glycosylated flavanones, like hesperidin or narirutin, that are natural compounds of citrus coproducts (Viuda-Martos et al 2010a) Reaction with reducing agents present in the formulation or with endogenous substances For example, when the pH of the meat is less than six, the nitrite added or that arising from the microbial reduction of nitrates is transformed 323 into nitrous acid (relatively unstable) This, in turn, reacts with endogenous (cysteine, reduced nicotinamide adenine dinucleotide, cytochromes, and quinines) or exogenous (ascorbic acid and its salts) reducing substances of the meat and is transformed into NO, completing the dismutation reaction, as described by P´erez-Alvarez (2006) Action of bacteria with nitrite-reductase activity such as Staphylococcus carnosus, Staphylococcus simulans, or Staphylococcus saprophyticus (Gøtterup et al 2007) The action mechanism through which strains of Staphylococcus use nitrate/nitrite is thought to be related with its capacity to act as alternative electron acceptor in the cell respiratory chain (Gøtterup et al 2008) The synthesis of nitrite reductases only occurs in anaerobic conditions and is induced by the presence of nitrate or nitrite in the medium (Neubauer and Găotz 1996) Combined method, reducing the quantity of residual nitrite by interaction with natural ingredients (tomato paste, annatto) Thus, Deba et al (2007) reported that the addition of tomato paste to frankfurters reduces the added nitrite level from 150 to 100 mg/kg without any negative effect on the processing and quality characteristics of the product during storage Reaction with compounds present in citric coproducts such as orange and lemon albedo (Aleson-Carbonell et al 2003, Fern´andez-Gin´es et al 2004), orange dietary fiber (Fern´andez-L´opez et al 2008b, 2009), citrus fiber washing water (Viuda-Martos et al 2009b), orange fiber plus essential oils (Viuda-Martos et al 2010a, 2010b) ALTERATIONS IN MUSCLE-BASED FOOD COLOR The color of meat and meat products may be altered by several factors, including exposure to light (source and intensity), microbial growth, rancidity, and exposure to oxygen Despite the different alterations in color that may take place, few have been studied, including the pink color of boiled uncured products, premature browning (PMB), and melanosis in crustaceans Pink Color of Uncured Meat Products The normal color of a meat product that has been heat treated but not cured is “brown,” although it has recently been observed that these products show an anomalous coloration (red or pink) (Hunt and Kropf 1987) This problem is of great economic importance in “grilled” products, since this type of color is not considered desirable This defect may occur both in meats with a high hemoprotein content such as beef and lamb (red) and in those with a low concentration, including chicken and turkey (pink) (Conforth et al 1986) One of the principal causes of this defect is the use of water rich in nitrates, which are reduced to nitrites by nitrate-reducing bacteria, which react with the Mb in meat to form NOMb (Nash et al 1985) The same defect may occur in meat products containing paprika, which, according to Fern´andez-L´opez (1998), P1: SFK/UKS BLBS102-c17 P2: SFK BLBS102-Simpson 324 March 21, 2012 11:52 Trim: 276mm X 219mm Printer Name: Yet to Come Part 3: Meat, Poultry and Seafoods contains nitrates that, once incorporated in the product, may be similarly reduced by the microorganisms Conforth et al (1991) mentions that several nitrogen oxides may be generated in gas and electric ovens used for cooked ham and that these will react with the Mb to generate nitrosohemopigments Also produced in ovens is CO, which reacts with Mb during thermal treatment to form a pink-colored pigment, carboxyhemochrome It has also been described how the use of adhesives formed from starchy substances produces the same undesirable color in cooked products (Scriven et al 1987) The same anomalous color may be generated when the pH of the meat is high (because of the addition of egg albumin to the ingredients) (Froning et al 1968) and when the cooking temperature during processing is too low These conditions favor the development of a reducing environment that maintains the iron of the Mb in its ferrous form, imparting a reddish/pink color (as a function of the concentration of hemopigments) instead of the typical grayish-brown color of heat-treated uncured meat products Cooking uncured meat products, such as roast beef, at low temperatures (less than 60◦ C) may produce a reddish color inside the product, which some consumers may like This internal coloring is not related with the formation of nitrosopigments, but results from the formation of OMb, a phenomenon that occurs because MMb-reducing enzymatic systems exist in the muscle that are activated at temperatures below 60◦ C (Osborn et al 2003) Microbial growth may also cause the formation of a pink color in cooked meats, since these reduce the oxido-reduction potential of the product during their growth This is important when the microorganisms that develop in the medium are anaerobes, since they may generate reducing substances that reduce the heme iron When extracts of Pseudomonas cultures are applied, the MMb may be reduced to Mb (Faustman et al 1990) Recently, Gallego-Restrepo et al (2010) reported that microorganism can play an important role in the color of uncured meat products during its elaboration process These authors recommended the use of microbiological starter culture with a higher metabolic action at refrigeration conditions to obtain excellent color characteristics on this type of products Melanosis Melanosis or blackspot, involving the appearance of a dark, even black, color, may develop post mortem in certain shellfish during chilled and frozen storage (Slattery et al 1995) Melanosis is of huge economic importance, since the coloration may suggest a priori in the eyes of the consumer that the product is in bad condition, despite the fact that the formation of the pigments responsible involves no health risk Melanosis is an objectionable surface discoloration of high valuable shellfish as lobsters caused by enzymic formation of precursors of phenolic pigments Blackspot is a process regulated by a complex biochemical mechanism, whereby the phenols present in a food are oxidized to quinones in a series of enzymatic reactions caused by polyphenoloxidase (PO) (Ogawa et al 1984) This is followed by a polymerization reaction, which produces pigments of a high molecular weight and dark in color Melanosis is produced in the exoskeleton of crustaceans, first in the head and gradually spreading toward the tail Melanosis of shell and hyperdermal tissue in some shellfish as lobsters was related to stage of molt The molting fluid is considered as the source of the natural activator(s) of pro-PO Polyphenol oxidase (catechol oxidase) can be isolated from shellfish cuticle (Ali et al 1994) and still active during iced or refrigerated storage The process can be controlled by using sulfites (Ferrer et al 1989), although their use is prohibited in many countries Also ficin (Taoukis et al 1990), 4-hexylresorcinol, functioned as a blackspot inhibitor, alone and in combination with l-lactic acid (Benner et al 1994) Recently, Encarnacion et al (2010) reported that dietary supplementation of the Flammulina velutipes mushroom extract in shrimp could be a promising approach to control postmortem development of melanosis and lipid oxidation in shrimp muscles Premature Browning Hard-to-cook patties show persistent internal red color and are associated with high pH (>6) raw meat Pigment concentration affects red color intensity after cooking (residual undenatured Mb), so this phenomenon is often linked to high pH dark-cutting meat from older animals PMB is a condition in which ground beef (mince) looks well done at lower than expected temperature (Warren et al 1996) PMB of beef mince is a condition in which Mb denaturation appears to occur on cooking at temperature lower than expected and, therefore, may indicate falsely that an appropriate internal core temperature of 71◦ C has been achieved (Suman et al 2004) The relationship between cooked color and internal temperature of beef muscle is inconsistent and depends on pH and animal maturity Increasing the pH may be of benefit in preventing PMB but may increase incidence of red color in well-cooked meat (cooked over internal temperature of 71.1◦ C) (Berry 1997) When PSE meat is used in patties processing and those containing OMb easily exhibited PMB One of the reasons of this behavior is that percentage of Mb denaturation increased as cooking temperature increased (Lien et al 2002) Recently, Mancini et al (2010) reported that the use of several additives such as lactate improved raw color stability, but did not minimize PMB COLOR AND SHELF LIFE OF MUSCLE-BASED FOODS Meat and meat products are susceptible to degradation during storage and throughout the retail process In this respect, color is one of the most important quality attributes for indicating the state of preservation in meat Any energy received by food can initiate its degradation, the rate of any reactions depending on the exact composition of the product (Jensen et al 1998), environmental factors (light, temperature, presence of oxygen), or the presence of additives Transition metals, such as copper or iron, are very important in the oxidative/antioxidative balance of meat When the P1: SFK/UKS BLBS102-c17 P2: SFK BLBS102-Simpson March 21, 2012 11:52 Trim: 276mm X 219mm Printer Name: Yet to Come 17 Chemical and Biochemical Aspects of Color in Muscle-Based Foods free ions of these two metals interact, they reduce the action of certain agents, such as cysteine, ascorbate and α-tocopherol, oxidizing them and significantly reducing the antioxidant capacity in muscle (Zanardi et al 1998) The iron in meat is 90% heme iron (HI), which is several times more absorbable than nonheme iron (NHI) present in other foods (Fern´andez-L´opez et al 2008a) Although the mechanism for heme iron release in meat has not been determined, oxidation of the porphyrin ring and denaturation of Mb (Kristensen and Purslow 2001) are probably involved Harel et al (1988) reported that the interaction of MMb with H2 O2 or lipid hydroperoxide results in the release of free ionic iron Free ionic iron can serve as a catalyst in the production of a˙ OH from H2 O2 as well as in the degradation of lipid hydroperoxides to produce peroxyl and alkoxyl radicals, which can initiate lipid oxidation and/or be self-degraded to the secondary products of lipid oxidation (Min and Ahn 2005) However, reducing compounds are essential to convert ferric to ferrous ion, a catalyst for Fenton reaction Lee et al (1998) reported that during refrigerated storage of meat, there is a release of iron from the heme group, with a consequent increase in NHI, which speeds up lipid oxidation Also, the heme molecule can break down during cooking or storage (G´omez-Basauri and Regenstein 1992a, 1992b, Miller et al 1994a, 1994b) and can generate NHI The increase of NHI in meats and fish is considered to be a reflection of the decrease of HI and is linked to the oxidative deterioration (Schricker and Miller 1983) Nonheme iron is considered the most important oxidation promoter in meat systems, and therefore, knowledge of the proportions of the chemical forms of iron is of great importance (Kanner et al 1991) An increase in the amount of NHI as a result of thermal processes on meat systems has been demonstrated by several authors (Schricker et al 1982, LombardiBoccia et al 2002) Gomez-Basauri and Regenstein (1992a, 1992b), suggested cooking is not as important as the subsequent refrigerated storage of cooked meats for the release of NHI from Mb The relationship between oxidative processes and the release of iron from Mb and the effect of these chemical changes on color characteristics of cooked products is still not well understood The increase of NHI could have some important consequences, affecting both the nutritional and technological properties of liver pate The degradation of heme iron would reduce the nutritional value of the pates in terms of bioavailability of iron, since HI is more available than NHI (Hunt and Roughead 2000) Furthermore, iron achieves enhanced ability for promoting oxidation processes when it is released from the heme molecule (Kanner et al 1991), and therefore, pates with increasing amounts of NHI might also have increased oxidative susceptibility From a nutritional point of view, Ahn and Kim (1998) reported that the status of ionic iron is more important than the amount of iron Traditionally, researchers have determined the discoloration of meat using as criterion the brown color of the product, calculated as percent of MMb (Mancini et al 2003) These authors 325 demonstrated that in the estimation of the shelf life of beef or veal (considered as discoloration of the product), the diminution in the percent of OMb is a better tool than the increase in percent of MMb Occasionally, when the meat cut contains bone (especially in pork and beef), the haemopigments (mainly Hb) present in the medulla lose color because the erythrocytes are broken during cutting and accumulate on the surface of the bone Hb When exposed to light and air, the color of the Hb changes from bright red (OHb) characteristic of blood to brown (MHb) and even black (Gill 1996) This discoloration basically takes place during long periods of storage and especially during shelf life display (Mancini et al 2004) This characteristic is aggravated if the product is kept in a modified atmosphere rich in oxygen (Lanari et al 1995) These authors also point out that the effect of bone marrow discoloration is minimized by the effect of bacterial growth in modified atmosphere packaging As in the case of fresh meat, the shelf life of meat products is limited by discoloration (Mancini et al 2004) This phenomenon is important in this type of product because they are normally displayed in illuminated cabinets Consequently, the possibility of nitrosated pigments photo-oxidation of (NOMb) needs to be taken into account During this process, the molecule is activated because it absorbs light; this may subsequently deactivate the NOMb and give the free electrons to the oxygen to generate MMb and free nitrite In model systems of NOMb photo-oxidation, this effect can be diminished by adding solutions of dextrose, which is a very important component of the salts used for curing cooked products and in meat emulsions When a meat product is exposed to light or is stored in darkness, the use of ascorbic acid or its salts may help stabilize the product’s color Such behavior has been described both in model systems of NOMb (Walsh and Rose 1956) and in dry-cured meat products (e.g., “longanizas” and Spanish dry-fermented sausage) However, when sodium isoascorbate or erythorbate is used in “longaniza” production, color stability is much reduced during the retail process (Ru´ız-Peluffo et al 1994) The discoloration of white meats like turkey is characterized by a color changes, which go from pink/yellow to yellow/brown, while in veal/beef the changes go from purple to grayish/brown In turkey, it has been demonstrated that the presence or absence of lipid oxidation depends on, among other things, the concentration of vitamin E in the tissues The color and lipid oxidation are interrelated, since it has been seen that lipid oxidation in red and white muscle depends on the predominant form of catalyzing iron, Mb, or free iron (Mercier et al 1998) Compared with red meat, tuna flesh tends to undergo more rapid discoloration during refrigerated storage Discoloration due to oxidation of Mb in red fish presented a problem, even at low temperature This low color stability might be related to the lower activity or poorer stability of MMb reductase in tuna flesh (Ching et al 2000) One of the reasons of this behavior is that aldehydes known to be produced during lipid oxidation can accelerate tuna OMb oxidation in vitro (Lee et al 2003) Also, tuna flesh could be immersed in MMb reductase solution that could extend the color stability of tuna fish Also, the use ... each showed different absorbance bands (AB); thus, MHb showed AB at 406, 500, and 630 nm; OHb showed 4 18, 540–542, 516–5 78, 950 nm; and DHb showed 430, 555, 760, and 910 nm From technological point... other foods (Fern´andez-L´opez et al 2008a) Although the mechanism for heme iron release in meat has not been determined, oxidation of the porphyrin ring and denaturation of Mb (Kristensen and. .. excessively bright or shiny lowers the carcass and cut price Fat with a yellowish color in healthy animals reflects a diet containing beta-carotene (Swatland 1 988 ) While fat color evaluation has traditionally