Veal colour assessment with three wavelengths

A method to derive reflectance spectra and colour coordinates of meat by measurement of reflectance at only three wavelengths, 480, 570 and 620 nm has been developed, by treating the spectra of a meat sample as a linear combination of the spectra of the three major myoglobin derivatives (reduced myoglobin, oxymyoglobin and metmyoglobin). Applied to 300 samples of Semitendinosus and Longissimus dorsi veal muscles at different times post mortem (24 h to 9 d), colour differences ΔE (?) between the derived spectra and the real ones were about 1.5 units. The total pigment content, with high correlation with the extraction method (P < 0.02), and the relative proportions of the derivatives can also be estimated.     

Structural changes of myoglobin in pressure-treated pork meat probed by resonance Raman spectroscopy

Pork meat was pressurised at 600–700 MPa under conditions applicable for non-thermal food preservation and studied by resonance Raman spectroscopy with 413-nm excitation to probe selectively myoglobin, which is the origin of the red colour of meat. The spectra of intact, non-pressurised meat tissue exclusively display the resonance Raman bands of the ferrous deoxy-form of myoglobin whereas upon pressure treatment a new six-coordinated low spin ferrous species is formed (>60%), that is assigned to a bis–histidine complex including the distal histidine 64. This structural change is associated with a shift of the electronic transitions of the haeme and thus affects the colour of the meat. In contrast, solutions containing myoglobin extracted from pressurised and non-pressurised pork meat give rise to resonance Raman spectra characteristic of the ferrous oxy-form of myoglobin, evidently due to the accessibility of the proteins for oxygen in solution. Upon pressure treatment of the extracted myoglobin solution, the oxy-form is partially converted to the met-(like) ferric form implying a pressure-induced oxidation of the haeme. Thus, this structural transition does not only cause a colour change but also may initiate unwanted oxidative side reactions involving further components of meat. Evidently, such effects can be largely avoided when the oxy- to deoxy-myoglobin ratio is kept small prior to pressure treatment.     

The effect of ionising radiation on the CIELAB colour co-ordinates of chicken breast meat as measured by different instruments

The colour of irradiated and unirradiated chicken breasts was measured at two laboratories (A & B). The effect of instrumental differences on the CIELAB colour co-ordinates and reflex attenuance spectra of the chicken breasts was examined. Each laboratory used two spectrophotometers, one of which was common to both. Laboratory B operated their other spectrophotometer in two different measuring geometries. Irradiated chicken breasts were found to exhibit increased a* values (greater redness) when compared with the unirradiated controls. Although differences in absolute CIELAB co-ordinates were found between instruments, all the instruments evaluated indicated increased redness and chroma values for the irradiated samples. Examination of reflex attenuance spectra indicated that the increases in a* observed were due to lesser absorption of light in the 600–700 nm region, although evidence of a change in pigment form was limited.     

Analysis of meat pigments with tissue spectrophotometer TS-200

The colour of meat and rice flour pastes containing known amounts of myoglobin and the colour of intact beef and pork samples were analyzed with tissue spectrophotometer TS-200. The differences in the spectra of myoglobin among three types of derivatives were successfully distinguished with this instrument. In addition, there is a close relationship between I_HB value, a parameter for estimating the content of pigments in animal tissues, and myoglobin content in model systems (rice flour paste and meat paste). Especially, the I_HB value is proportional to myoglobin content in intact beef and pork meat whose myoglobin is mostly in the state of oxymyoglobin and/or deoxymyoglobin: Y = 208·26 x + 6·72, where y is the I_HB value, x is the myoglobin content (%) and R = 0·94.     

Near-infrared oximetry of three post-rigor skeletal muscles for following myoglobin redox forms

We investigated the response of frequency-domain multidistance (FDMD) near-infrared (NIR) tissue oximetry for detecting absolute amounts of myoglobin (Mb) redox forms and their relationship to meat colour stability. Four packaging formats were used to create different blends of Mb redox forms and meat colours during display. Changes in surface colour and subsurface pigment forms during simulated display time (0, 2, 4, and 10 d at 2 °C) were evaluated using surface reflecto-spectrophotometry (both L∗a∗b∗ and specific wavelengths) and FDMD NIR tissue oximetry. Data for both methods of direct measurement of oxymyoglobin and deoxymyoglobin were strongly related and accounted for 86–94% of the display variation in meat colour. Indirect estimates of metmyoglobin ranged from r² = 59–85%. It appears that NIR tissue oximetry has potential as a noninvasive, rapid method for the assessment of meat colour traits and may help improve our understanding of meat colour chemistry in post-rigor skeletal muscle.     

Contribution of pigment content, myoglobin forms and internal reflectance to the colour of pork loin and ham from pure breed pigs

The colour of loin, M. longissimus dorsi (LD), and ham, M. biceps femoris (BF), from pure breed Hampshire, Swedish Landrace and Swedish Yorkshire pigs was studied. The contribution of the pigment content, the myoglobin forms deoxymyoglobin (Mb), oxymyoglobin (MbO) and metmyoglobin (MetMb) and the internal reflectance to the colour of pork of normal meat quality was evaluated using partial least squares regression (PLS). The colour of LD and BF from the Hampshire breed was more red and yellow and more saturated than the colour of the same muscles from the Swedish Landrace and the Swedish Yorkshire breeds. Furthermore, BF from Hampshire was darker than BF from the other two breeds. These differences in colour were related to the lower pH in Hampshire, resulting in more blooming and in higher internal reflectance, and to the higher pigment content. The colour of BF was darker and more red than the colour of LD within each breed. No colour difference was found between gilts and castrates within each breed. Most of the variation (86-90%) in lightness (L* value), redness (a* value) and yellowness (b* value), chroma (saturation) and hue angle of pork of normal meat quality was explained by the pigment content, myoglobin forms and internal reflectance. The L* value, a* value, chroma and hue angle were influenced by both the pigment content and by the myoglobin forms to almost the same extent, while the internal reflectance was of no significance to these colour parameters. The b* value was influenced most by the myoglobin forms, less by the internal reflectance and almost not at all by the pigment content.     

Effect of transport time and ageing on aspects of beef quality

Forty-eight bulls were transported by road in groups of eight for approximately 30 min, 3 or 6 h in two replicates. After slaughter, steaks from the longissimus dorsi thoracis of all transported animals were analysed in terms of pH, water-holding capacity, myoglobin concentration, texture at 7 and 14 days of ageing (compression and Warner-Bratzler analyses) and colour of the same surface of meat cut at 24 h post-mortem and allowed to bloom for 24 h and 7 d (L^*a^*b^*, chroma and hue). The myofibrillar resistance of the meat from animals transported 30 min was significantly greater at 20% compression (P<0.05). The maximum load and a^*b^* and chroma were all lower for meat aged 14 days.     

The kinetics of cooked meat haemoprotein formation in meat and model systems

The rate of cooked meat haemoprotein formation (measured as the rate of loss of myoglobin solubility) was found, at least initially, to obey first order kinetics in meat, aqueous muscle extracts and mixtures of myoglobin and bovine serum albumin. In meat at 60 °C the rate was dependent on the species, (the pigment was formed significantly faster in lamb m. longissimus dorsi than in beef m. longissimus dorsi) and anatomical location (cooked meat haemoprotein was formed in beef m. 1. dorsi about twice as rapidly as in both beef shin and chuck (shoulder) muscle of similar pH). The rate of formation was similar in aqueous muscle extracts to that found in meat and in these systems increased with decreasing pH. The activation energies for all beef systems studied were similar and typical of those associated with protein denaturation (˜300 KJ mol⁻¹); however, that from lamb appeared to be lower (˜200 KJ mol⁻¹). The problems of using colour as an index of temperature reached, either for microbial safety (E. Coli 0157:H7 destruction) or quality are discussed in the light of these results.     

Biochemical factors influencing metmyoglobin formation on beef from muscles of differing colour stability

Biochemical parameters, such as oxygen consumption rate by muscle post mortem (OCR), depth of oxygen penetration into meat, rates of myoglobin oxygenation and deoxygenation and myoglobin content and succinic dehydrogenase activity, were determined for muscles of differing colour stability. Metmyoglobin reduction, in anoxia following oxidation with ferricyanide (MRA) and aerobically following oxidation with low pO(2) (ARA), were also determined. M. psoas major (poor colour stability) has higher enzymic activity than M. longissimus dorsi (good colour stability). This difference, together with the low myoglobin content in M. psoas major, results in relatively high OCR with consequent low oxygen penetration and rapid conversion of oxymyoglobin to myoglobin in M. psoas major, disposing it to rapid formation of metmyoglobin. Metmyoglobin reduction occurs both under anaerobic and aerobic conditions but no significant correlation is found between actual metmyoglobin reduction and rate of discoloration of different muscles. The most significant factor affecting colour stability of beef muscles appears to be their enzymic activity which determines the rate of myoglobin oxidation.     

Contribution of nitrite and nitrate to the colour and flavour of cured meats

The formation of nitric oxide myoglobin from nitrite and myoglobin involves a complex series of reactions not all of which are completely understood even now, and the stability of the cured colour, so important from the marketing point of view, continues to be investigated. The amount of nitrite necessary for complete formation of nitric oxide myoglobin is very small and the presence of no more than 25 mg/kg of nitrite in the cured meat is enough to ensure an adequately stable colour. At least four times this level is essential to produce a full development of the typical cured flavour. Very little is known of the mechanism of the reactions leading to the formation of cured flavours in cooked products or of the identity of the volatile substances responsible for it.     

Effect of finishing mode (pasture- or mixed-diet) on lipid composition, colour stability and lipid oxidation in meat from Charolais cattle

Effects of pasture- or mixed-diet finishing mode on colour and lipid stability were measured in meat from Charolais steers, heifers and cows of different ages after refrigerated storage. Meats from pasture- and mixed-diet finished cattle have more or less significant differences in lipid composition which will influence the colour and lipid stability. The mixed-diet finished cattle have about the same proportions of saturated and monounsaturated lipids as pasture-diet finished animals; on the contrary, cattle fed on grass have higher proportions of n-3 PUFA, and to a less extent, of n-6. Finishing diet had an important effect on lipid stability, meat from pasture-finished animals showing significantly lower TBA-RS level than meat from mixed-diet finished animals. Effect of diet was also significant on myoglobin content with a higher content of haeminic iron in mixed-diet finished animals. Effect of diet on colour stability was slight with a beneficial effect of pasture finishing mode, significant only in heifers, and after a meat storage of six days in air.     

Effects of malate,lactate, and pyruvate on myoglobin redox stability in homogenates of three bovine muscles

We investigated the effects of glycolytic and tricarboxylic acid cycle metabolic intermediates on myoglobin redox forms and meat colour stability. Eighteen combinations of malate (M), lactate (L), and pyruvate (P) were added to beef Longissimus lumborum, Psoas major, and Semitendinosus muscle homogenates to study their effect on metmyoglobin formation during incubation at 25 °C. Changes in surface colour at 0, 2, 4, 8, and 12 h were evaluated by using reflecto-spectrophotometry [both L*, a*, and b* and wavelengths specific for metmyoglobin (MMb)]. Addition of M, L, and P alone or in combinations stabilized (P < 0.05) L*, a*, and b* values and myoglobin redox forms in muscle homogenates; however, there was a trend for P to be least effective. At the 2% concentrations for the individual metabolites, L was most effective at retarding MMb formation in the Semitendinosus (M was intermediate and P was least effective), and M was most effective in the Psoas major and L. lumborum muscles (L was intermediate and P was least effective). Metmyoglobin was reduced most effectively with a combination of metabolites (M + L > M + P > L + P). Enhancing meat with these metabolites can effectively extend colour life of post-rigor meat, apparently by providing more reducing conditions for myoglobin, thus increasing myoglobin redox form stability.     

The change in meat pigments in sausage making processes

The colour of cured meat and sausages depends essentially on the chemical modifications of the natural pigments of animal muscle. This paper deals with the influence of processing on the pigments and the control of their transformation by studying the refletion spectra of the surface of the samples. It is demonstrated that better curing conditions may be obtained by accurate control of the chemical modifications of pigments during the different stages of processing: curing, smoking, drying, etc. The keeping qualities of non-heated cured meat products (e.g., fermented sausages) depend essentially on the efficiency of the nitrosation process. Incomplete nitrosation of the porphyric pigments increases the sensitivity to discoloration by a Fe²⁺ → Fe³⁺ oxidation of the residual native myoglobin.     

Effects of three lighting intensities during display on discolouration of beef semitendinosus muscle

This study focuses on the changes in colour parameters of beef (semitendinosus muscle) upon the light exposure. In one of the experiments (Experiment I), colour parameters were studied during 60 min of blooming. In the Experiment II, the changes of colour over 168 h of exposure were evaluated. For this purpose, the white fluorescent light of three different intensities, 500, 1,000 and 1,500 lx, was chosen. It is shown that it takes up to 16–18 min for the colour parameters to stabilize after the steak cutting, which is a consequence of increasing availability of oxygen. Beef colour is affected by the light intensity. It was observed that at the beginning of the light exposure, favourable changes took place. However, after few days of exposure to the light, meat colour deteriorates significantly. Changes are mainly related to the redness (a*). The value of a* decreased about 4–7 units (p < 0.05) after 7 days of meat exposure. This significant change of redness is also clearly evident in the visual assessment. White fluorescent light (colour temperature of 3,000 K) with intensity of 500 lx has lower impact on the beef colour than the light with intensity of 1,000 or 1,500 lx. Intensity of 500 lx is more favourable to preserve the desired beef colour, and it could be recommended to use in the retail display. However, further studies taking into account the visual evaluation of beef colour would be useful to confirm this fact.     

Redox processes in pressurised smoked salmon studied by resonance Raman spectroscopy

Non-thermal food preservation technology is based on the application of high pressures up to 600 MPa. Here we report a resonance Raman (RR) spectroscopic analysis of smoked salmon meat after high pressure processing. High quality spectra, which can be obtained even from packed salmon without spectral interference of the packing foil, allow determining pressure-dependent irreversible changes of the main RR-active components of salmon meat, astaxanthin and myoglobin/haemoglobin. High pressure-treatment causes a decrease of the relative RR intensities of astaxanthin as probed with 514 nm excitation which is in line with a slight attenuation of the originally intense red colour of the salmon meat. 413-nm excited RR spectra indicate a heterogeneous broadening of astaxanthin bands accompanied by the formation of deoxy-myoglobin or deoxy-haemoglobin. The results suggest that pressure-treatment facilitates the oxidative degradation of astaxanthin coupled to the reduction of metmyoglobin (methaemoglobin).     

Carcass and meat quality in light lambs from different fat classes in the EU carcass classification system

Ninety commercial lamb carcasses were analysed according to the four different fat classes in the light lamb European classification system. Shoulder fat increased 3%, muscle decreased 2% and bone decreased 1% for each class increase. No significant differences were found among fat classes regarding pH, WHC, cooking losses, juiciness, myoglobin content, meat colour measured immediately after cutting (L*, a*, b*), odour intensity or flavour quality. Some differences were found in colour evolution through ageing. Shear force decreased and tenderness and flavour intensity increased with fat class but this effect was only significant in the leanest animals.     

A multispectral imaging technique to determine concentration profiles of myoglobin derivatives during meat oxygenation

We have designed a multispectral imaging acquisition system to measure the relative concentration values of myoglobin forms inside meat during oxygenation. Images at 474, 525, 572 and 610 nm are used to compute the concentration of reduced myoglobin, oxymyoglobin and metmyoglobin with a spatial resolution of 0.0125 mm/pixel. From these images, pigment concentration profiles as a function of oxygenation time and depth beneath the surface were obtained. A model describing the diffusion of oxygen and the consumption of reduced myoglobin is numerically tested versus the measured concentration profiles. The model accurately fits the data with a Mean Root Squared Error equal to 0.253%. Precise definitions for position and width of pigment layers based in concentration profiles are given. The results suggest that multispectral imaging techniques combined with precise control and measurement of sample temperature and oxygen partial pressure will permit detailed studies of the myoglobin chemistry during oxygenation.     

Colour changes after carcasses decontamination by steam and lactic acid

The surface decontamination of meat by steaming and by lactic acid prolongs its shelf life. Possible changes of colour were evaluated by reflectance spectrophotometry and video image analysis (VIA). Reflectance spectra were measured using a D₆₅ source and CIELab values L^*, a^* and b^* were calculated together with ratios of the different myoglobin forms (red, oxy, met). The same samples were evaluated by video image analysis (software LUCIA). Steaming and spraying with lactic acid increased slightly the lightness (L^*) of the meat surface. Coordinate a^* (redness) decreased slightly after the decontamination treatment. This was confirmed by VIA; brightness increased and red-ratio r decreased. Both methods, i.e. reflectance spectrophotometry and VIA, reflect the colour changes in a similar way. The main advantage of reflectance spectrophotometry was its higher sensitivity and the possibility of direct calculation of the ratio of the haem pigment forms. However, video image analysis allows analysing of different particles in the image and this method is therefore a suitable tool for monitoring the changes of the surface appearance.     

Stability of haem pigments in model systems and cooked meat

The stability of sheep haemoglobin and myoglobin in aqueous solution at 80, 100 and 121°C for 1 h was measured by subjecting portions of the heated solutions to electrospray mass spectrometry (ESMS). ESMS dissociates haem proteins into the globin chains and the haem moiety and, with haemoglobin, degradation of the α-(15047·5 Da) and β-(16073·3 Da) chains was observed at all heating temperatures. Under the same conditions, sheep myoglobin dissociated into the globin (16923·2 Da) and haem parts but the globin was stable and few degradation products were observed in the ESMS trace (mass range 4-20 kDa) even after 1 h at 121°C. There did seem to be limited breakdown of the globin due to loss of 170 Da. From the amino acid sequence, it is postulated that this is due to loss of GLY-LEU from the N-terminus. Methods for extracting myoglobin from raw and cooked meat were then investigated. Water was adequate for myoglobin extraction from raw meat but urea solution was required for adequate extraction of cooked meat samples. Sheep meat was heated at 80, 100 and 121°C in sealed cans, extracted and the mass profile in the range 4-20 kDa measured. Myoglobin was the major peak when samples were heated for 10, 20, 30 and 40 min. After that time, other peaks appeared although the myoglobin globin chain was still apparent. The results are discussed in relation to using myoglobin as a marker for meat speciation.     

Colour stability and lipid oxidation of fresh beef. Development of a response surface model for predicting the effects of temperature, storage time, and modified atmosphere composition

Samples of fresh beef muscles (Longissimus dorsi) were packed under varying modified atmosphere conditions (20-80% oxygen) and stored at 2-8°C for 10 days. At 2 day intervals meat samples were analysed for surface colour and extent of lipid oxidation (TBARS). Response surface models for predicting the effects of temperature, storage time and modified atmosphere composition on colour stability and lipid oxidation were developed. Temperature and time were found to be the most important factors for retaining meat colour and minimizing lipid oxidation. However, the oxygen content also had a significant effect on both quality parameters. A stable interval of maintaining a good meat colour was found between 55 and 80% O(2). Response surface modelling was found to be very promising for modelling of chemical quality changes in meat stored under different conditions, but the large biological differences between animals may complicate the development of generally valid models.