ON THE NATURE OF COOKED MEAT HEMOPROTEIN

Cinnamon bark deodorised aqueous extract as potential natural antioxidant in meat emulsion system: a comparative study with synthetic and natural food antioxidants

Cinnamon deodorised aqueous extract (CinDAE) was prepared and evaluated for its total phenolic (315.3 ± 35.4 mg GAE/g) and flavonoid (99.3 ± 9.6 mg RE/g) contents. Stabilizing efficiency of CinDAE, for chicken meatballs, was measured against oxidative deterioration as function of storage time under chilled conditions. For this purpose, oxidative stability [2-thiobarbituric acid reactive substances (TBARS); peroxide value (PV)], colour and sensory acceptability were measured in the control meatballs (C), and those stabilized with 200 ppm of: CinDAE (T1), ascorbic acid (T2), BHA/BHT (50/50; w/w) (T3). In comparison to "C", induction period (IP) and redness (a* value) of the stabilized samples (T1, T2 and T3) were increased, while PV and TBARS were decreased throughout storage (8 ± 1 °C) significantly (p < 0.05). Meanwhile, CinDAE slightly decreased L* value of the meatballs as compared to other tested samples. Conclusively, CinDAE improved stability and redness of chicken meatballs without negatively affecting its sensory acceptability (Hedonic test) up to a comparable extent to that of ascorbic acid/BHA/BHT and may potentially function as a dietary antioxidant for meat products.

Effect of heating oxyhemoglobin and methemoglobin on microsomes oxidation

Hemoglobin (Hb) has been proposed to be a major pro-oxidant in raw and cooked meats. To understand the mechanisms and differentiate between the pro-oxidant and antioxidant potential of oxyhemoglobin (OxyHb) and methemoglobin (MetHb), their pro-oxidant activity, protein solubility, radical scavenging capacity, iron content and contribution of non-chelatable iron on lipid oxidation were determined as a function of thermal treatments. The ability of native OxyHb and MetHb to promote lipid oxidation was similar and higher than their corresponding OxyHb or MetHb heated at 68 and 90 degrees C but not different from those at 45 degrees C. The pro-oxidant activity of MetHb heated at 68 and 90 degrees C were similar whereas the pro-oxidant activity of OxyHb heated at 68 degrees C was higher than that heated at 90 degrees C. The decreased pro-oxidant activity of heat-denatured Hb was associated with a decrease in the solubility of heme iron while free iron showed little impact on the lipid oxidation.

Effect of heating oxymyoglobin and metmyoglobin on the oxidation of muscle microsomes

Myoglobin (Mb) and its iron have been proposed to be major prooxidants in cooked meats. To understand the mechanisms and differentiate between the prooxidant and antioxidant potential of oxymyoglobin (OxyMb) and metmyoglobin (MetMb), their prooxidant activity, iron content, solubility, free radical scavenging activity, and iron binding capacity were determined as a function of thermal processing. The ability of native and heat denatured OxyMb and MetMb to promote the oxidation of muscle microsomes was different. MetMb promoted lipid oxidation in both its native and denatured states. Conversely, OxyMb became antioxidative when the protein was heated to temperatures >or=75 degrees C. The increased antioxidant activity of heat denatured OxyMb was likely due to a decrease in its prooxidative activity due to its loss of solubility. These data show that the impact on oxidative reactions of Mb is the result of the balance between its antioxidant and prooxidant activities.

[Effect of heat on the solubility and the electrophoretic behavior of myoglobin]

The heat stability of beef myoglobin was investigated by means of its solubility and intensity of protein bands separated by isoelectric focusing. A method for the sensitive determination of myoglobin in the extracts was developed based on its ability to form a red dye by the oxidative coupling of 2,4-dichlorophenol and 4-aminoantipyrine in the presence of hydrogen peroxide. By this method, myoglobin could be determined to a concentration of 0.01 mg/ml. For the detection of electro-focused myoglobins, o-dianisidine has proved to be the most sensitive compound. The myoglobin content of the extracts, according to the intensity of the myoglobin bands in the electrophoretic gel, decreased with increasing temperature and heating-time. However, the position of the bands was not changed by the heat treatment.

A note on the nature of the haematin pigments present in freeze dried and cooked beef

Analysis of the reflectance spectra of beef samples treated to contain all the haemoproteins in one pigment form indicated that little or no change in the haematin environment occurs on freeze drying fresh, oxymyoglobin-rich meat or cooked meat. Dehydration of metmyoglobin in meat results in the water molecule at the sixth coordination site being replaced by a protein-bound ligand. On rehydration, this ligand may be replaced by water to reform metmyoglobin, but the degree of conversion depends on the rate of rehydration. The spectral similarity between cooked and freeze dried, oxidised meat indicates that the haematin environments are similar. It is suggested that in these meats the predominant pigments are di-imidazole complexes.

Functionality of muscle proteins in gelation mechanisms of structured meat products

Recent advances in muscle biology concerning the discoveries of a large variety of proteins have been described in this review. The existence of polymorphism in several muscle proteins is now well established. Various isoforms of myosin not only account for the difference in physiological functions and biochemical activity of different fiber types or muscles, but also seem to differ in functional properties in food systems. The functionality of various muscle proteins, especially myosin and actin in the gelation process in modal systems which simulate structured meat products, is discussed at length. Besides, the role of different subunits and subfragments of myosin molecule in the gelation mechanism, and the various factors affecting heat-induced gelation of actomyosin in modal systems are also highlighted. Finally, the areas which need further investigation in this discipline have been suggested.

Availability of iron from chicken meat and liver given to rats

The concentration and distribution of iron in 59Fe-labelled chicken leg and breast meat and liver were determined by gel filtration. In all samples approximately 50% of the Fe was insoluble (haemosiderin) and the haemoproteins (haemoglobin and myoglobin) constituted from 15% (liver) to 25% (leg meat) of the total Fe. Ferritin accounted for from 12% (leg meat) to 27% (liver) of the total Fe. A technique was developed which enabled the time-course of the passage of 59Fe-labelled whole and fractionated meat and liver through the gastrointestinal tract of Fe-replete and Fe-deficient rats to be followed and it was found that the rate of stomach emptying appeared to be a function of the viscosity of the meal. In Fe-replete rats approximately 71% of a meal of raw chicken meat had left the stomach within 1 h of administration and by 2 h the stomach was almost empty and much of the unabsorbed 59Fe was in the ileum. By 4 h the ileum and colon contained almost equal amounts of 59Fe. Between different test meals there were only slight differences in gastrointestinal distribution and these reflected the different rates of stomach emptying. Stomach emptying was slower in Fe-deficient compared with Fe-replete rats. In Fe-replete, but not Fe-deficient, rats it was found that the amount of 59Fe lost (absorbed) from the gastrointestinal tract 2 h after administration of a test meal was not significantly different from the value found using a 7 d faecal collection technique. Comparison of the 2 h absorption values for several test meals indicated that 59Fe absorption from raw whole meat was significantly higher than from the soluble extract and the residue after extraction (haemosiderin). Heat treatment caused a significant decrease in the absorption of Fe in whole meat and the soluble meat extract but a significant increase in the liver absorption values. It is suggested that denatured haemoproteins are less available for absorption than their native forms but that heating increases the availability of the Fe of haemosiderin or ferritin or both. Isolated muscle ferritin was poorly absorbed but on the addition of excess bovine serum albumin the absorption of the Fe was markedly increased. It is concluded that, to estimate the Fe availability of a food such as chicken meat or liver one must not only take account of the concentration and type of each Fe-containing compound present but also such factors as their possible synergistic effects, the presence of chelating agents, the extent of cooking and the concentration and type of proteinaceous digestion products.