Meat science from 1976: A history of the journal.

The journal Meat Science was first published in 1976/77 and it initially comprised 4 issues per year. The first issue contained 4 papers and the first volume (4 issues) contained 27 articles, a mixture of papers and research notes. Its growth/popularity increased, and it has continued to thrive and in 2016 of the 1010 papers processed 292 were accepted. Over 90% of the papers published in the first volume were concerned with muscle biochemistry/meat properties. During the last years of the 20th century, meat products and their properties became a far larger proportion of the submissions as did those concerned with nutrition and safety. More recently there has been a resurgence of papers concerned with meat quality. Over the last 40years, the journal has reported on the major developments in meat science research and this paper will discuss both the history of the journal, and aspects of meat research as reflected in its publications. Possible future research trends are also discussed.

High pressure processing of fresh meat--is it worth it?

When subjected to high pressures at ambient temperatures, the shelf life of fresh meat is increased; however the meat takes on a cooked appearance as the actomyosin denatures at about 200MPa and the myoglobin denatures and/or co-precipitates with other proteins at about 400MPa. In addition, at pressures of 400MPa and above the unsaturated lipids in the meat become more susceptible to oxidation, probably due to the release of iron from complexes present in meat (haemosiderin and ferritin?) and/or changes in the lipid membrane. Thus, even if legislation allowed it, it is unlikely that many consumers would be prepared to buy such meat. However if pre-rigor meat is subjected to pressures of about 100-150MPa, below those necessary to cause colour changes, it becomes significantly more tender than its untreated counterpart and this may now be a commercially viable process, given the decreasing cost of high pressure rigs. When treated at 100-200MPa while the temperature is raised from ambient to around 60°C post-rigor meat also yields a tender product and this may also be a commercially attractive process to parts of the food industry, for example those involved in catering.

Microstructure and thermal characteristics of Thai indigenous and broiler chicken muscles.

The microstructure and thermal characteristics of Thai indigenous (Gallus domesticus) and broiler chicken (commercial line CP707) biceps femoris and pectoralis muscles were determined. Perimysium thicknesses were 14.2 microm for biceps femoris muscle and 7.10 microm for pectoralis muscle of indigenous chicken muscles, thicker than those of broiler muscles, which were 9.93 microm for biceps femoris muscle and 3.87 microm for pectoralis muscle (P < 0.05). Five endothermic peaks with peak transition temperatures (Tp) of 54.9, 61.7, 65.4, 70.6, and 76.1 degrees C were obtained for broiler pectoralis muscle, whereas only 3 endothermic peaks (Tp of 56.6, 62.6, and 74.9 degrees C) were obtained for broiler biceps femoris muscle. Thai indigenous biceps femoris and pectoralis muscles had endothermic peaks with Tp ranges of 53.5 to 54.8, 60.7 to 61.9, and 75.9 to 76.9 degrees C. The fiber diameters of Thai indigenous chicken muscles were greater (P < 0.05) than those of the broiler, 31.7 vs. 20.4 microm for biceps femoris muscle and 28.9 vs. 26.6 microm for pectoralis muscle, respectively. After cooking at 80 degrees C for 10 min, the fiber diameter of indigenous chicken muscles significantly decreased while those of the broiler significantly increased. The mean of sarcomere lengths of the raw muscles ranged from 1.56 to 1.64 microm and decreased to 0.92 to 1.32 microm (P < 0.001) for broiler muscles and 1.22 to 1.35 microm (P < 0.001) for indigenous chicken muscles after cooking. The perimysium and endomysium of broiler muscles melted after cooking at 80 degrees C, however, only slight disintegration was observed in these tissues in the indigenous chicken muscles.

Composition, color, and texture of Thai indigenous and broiler chicken muscles.

Chemical compositions and physical properties of mixed-sex Thai indigenous (Gallus domesticus) and broiler (commercial breed, CP707) chicken biceps femoris and pectoralis muscles were determined. Indigenous chicken muscles contained higher protein contents but lower fat and ash contents compared to broiler muscles (P < 0.001). The amino acid profile of the indigenous chicken muscles was similar to that of the broiler muscles except they were slightly richer in glutamic acid (P < 0.05). The indigenous chicken muscles contained more saturated and less polyunsaturated fatty acids than the broiler muscles. There were no differences in the monounsaturated fatty acid contents between the breeds. The total collagen contents of indigenous pectoralis and biceps femoris muscles were 5.09 and 12.85 mg/g, respectively, which were higher than those found in broiler pectoralis (3.86 mg/g) and biceps femoris muscles (8.70 mg/g) (P < 0.001). Soluble collagen contents were lower for indigenous pectoralis and biceps femoris muscles, 22.16 vs. 31.38% and 26.06 vs. 33.87%, respectively. The CIE system values of lightness (L*), redness (a*), and yellowness (b*) of indigenous chicken muscles were higher than those of broiler muscles. The shear values of indigenous chicken muscles either raw or cooked were higher than those of broiler muscles (P < 0.05). After cooking, the shear values decreased for broiler biceps femoris and pectoralis muscles (P < 0.05), whereas no change was observed for indigenous chicken biceps femoris muscle (P > 0.05). Shear values increased for indigenous chicken pectoralis muscle (P < 0.05).

High pressure/thermal treatment effects on the texture of beef muscle.

The effects of high pressure (to 800 MPa) applied at different temperatures (20-70 °C) for 20 min on beef post-rigor longissimus dorsi texture were studied. Texture profile analysis showed that when heated at ambient pressure there was the expected increase in hardness with increasing temperature and when pressure was applied at room temperature there was again the expected increase in hardness with increasing pressure. Similar results to those found at ambient temperature were found when pressure was applied at 40 °C. However, at higher temperatures, 60 and 70 °C it was found that pressures of 200 MPa caused large and significant decreases in hardness. The results found for hardness were mirrored by those for gumminess and chewiness. To further understand the changes in texture observed, intact beef longissimus dorsi samples and extracted myofibrils were both subjected to differential scanning calorimetry after being subjected to the same pressure/temperature regimes. As expected collagen was reasonably inert to pressure and only at temperatures of 60-70 °C was it denatured/unfolded. However, myosin was relatively easily unfolded by both pressure and temperature and when pressure denatured a new and modified structure was formed of low thermal stability. Although this new structure had low thermal stability at ambient pressure it still formed in both the meat and myofibrils when pressure was applied at 60 °C. It seems unlikely that structurally induced changes can be a major cause of the significant loss of hardness observed when beef is treated at high temperature (60-70 °C) and 200 MPa and it is suggested that accelerated proteolysis under these conditions is the major cause.

High temperature reduction of metmyoglobin in aqueous muscle extracts.

Oxymyoglobin in aqueous extracts of fresh beef longissimus dorsi muscles was initially oxidised to metmyoglobin during heat treatments at temperatures in the range 50-70 °C. The metmyoglobin then underwent reduction to a red pigment that was shown spectrally to be identical to oxymyoglobin. The formation of oxymyoglobin involved a heat induced precipitate that when removed from the solution, allowed oxidation to metmyoglobin to occur. However, on re-addition of the precipitate further reduction to oxymyoglobin took place. Dialysis of the muscle extract prior to heating markedly inhibited the reduction but addition of NADH to the dialysate permitted further reduction. The precipitate plus NADH caused oxymyoglobin formation in the presence of metmyoglobin but neither the precipitate nor NADH alone induced this formation. It is concluded that the initial conversion of oxymyoglobin to metmyoglobin on heating fresh beef muscle extracts was reversible and that the reverse reaction depended on the presence of both NADH and a muscle protein.

Effect of high-pressure treatment on lipoxygenase activity.

Solutions of commercial soybean lipoxygenase (100 microgram/ML in 0.2 M citrate-phosphate and 0.2 M Tris buffer were subjected to pressures of 0.1, 200, 400, and 600 MPa for 20 mm. The enzyme was stable at atmospheric pressure (0.1 MPa) over a wide pH range (5-9). In citrate phosphate buffer, the enzyme had maximum stability over the pH range 58 in untreated samples and after treatment at 200 MPa, but with increasing pressure, the pH stability range become narrower and centered around pH 78. The enzyme was more sensitive to acid than alkali, and at pH 9, it lost virtually all activity after pressurization at 600 MPa for 20 mm in both buffers. The activity of the crude enzyme extracted from tomatoes treated at 200 and 300 MPa for 10 mm was not significantly different from that of the untreated tomatoes, while a pressure of 400 MPa for 10 mm caused a significant decrease in activity and treatment at 600 MPa led to complete and irreversible activity loss. Compared to unpressurized tomatoes, treatment at 600 MPa gave significantly reduced levels of hexanal, cis-3-hexenal, and trans-2-hexenal, which are important contributors to "fresh" tomato flavor, and this was attributed to the inactivation of lipoxygenase.

Effect of high-pressure treatment on the texture of cherry tomato.

The effect of high-pressure treatment (200-600 MPa for 20 min) on the texture of cherry tomatoes and on the key softening enzymes (pectinmethylesterase and polygalacturonase) was investigated. When subjected to high-pressure treatment whole cherry tomatoes showed increasing textural damage with increasing pressures up to 400 MPa. However, treatment at pressures above 400 MPa (500-600 MPa) led to less apparent damage than treatment at 300 and 400 MPa; the tomatoes appearing more like the untreated samples. These visual changes were reflected in the texture (firmness) and amount of cell rupture in the tomatoes, with the least firmness and the most cell rupture being seen after treatment at 400 MPa. Light and scanning electron microscopy supported these observations. Although a sample of purified commercial pectinmethylesterase was partially inactivated at pressures above 200 MPa, irrespective of pH (4-9), in the whole cherry tomatoes no significant inactivation was seen even after treatment at 600 MPa, presumably because other components in the tomato offered protection or the isoenzymes were different. Polygalacturonase was more susceptible to pressure, being almost totally inactivated after treatment at 500 MPa. It is concluded that the textural changes in tomato induced by pressure involve at least two related phenomena. Initially, damage is caused by the greater compressibilty of the gaseous phase (air) compared to liquid-solid components, giving rise to a compact structure which, on pressure release, is damaged as the air rapidly expands, leading to increases in membrane permeability. This permits egress of water, and the damage also enables enzymatic action to increase, causing further cell damage and softening. The major enzyme involved in the further softening is polygalacturonase, which is inactivated at 500 MPa and above, and not pectinmethylesterase, which in the whole fruit, is barotolerant.

Prediction of the soluble myoglobin content of cooked burgers.

The time-temperature profiles for cooking in-house made beef and lamb burgers were determined using a thermocouple placed in the centre of the burger. From these data the soluble myoglobin remaining in the burger was predicted using kinetic data from previously reported model experiments. First order kinetics were assumed for the denaturation of the myoglobin. A good correlation between observed and predicted data was observed. Thus the "degree of doneness"of different meats can be predicted when cooked under specified conditions.

Effect of high hydrostatic pressure on the volatile components of a glucose-lysine model system.

An aqueous glucose-lysine model system (initial pH 10.1) was incubated at 60 degrees C and atmospheric pressure (system A) or 600 MPa (system B) to the same absorbance value at 420 nm. Volatile reaction products were isolated by solvent extraction and analyzed by gas chromatography/mass spectrometry. Thirty-two compounds were identified; most contained nitrogen, and pyrazines predominated. Yields of all compounds were suppressed at 600 MPa. Further incubation, at either atmospheric pressure (system C) or 600 MPa (system D), of system A, resulted in lower yields of many compounds at 600 MPa, compared to prolonged incubation at atmospheric pressure. Many of the compounds reported may be formed by, or subsequently react via, aldol condensation. The observed differences among the systems in the profiles and yields of volatile compounds suggest that aldol condensations increase in rate in the systems under pressure.

Effects of high pressure on the myofibrillar proteins of cod and turkey muscle.

When turkey breast muscle and isolated myofibrillar protein and myosin of cod or turkey (pH approximately 7) were subjected to pressures up to 800 MPa for 20 min, DSC and electrophoresis (SDS-PAGE) indicated that high pressure-induced denaturation of myosin led to the formation of structures that contained hydrogen bonds and were additionally stabilized by disulfide bonds. Disulfide bonds were also important in heat-induced myosin gels. Hardness of whole cod muscle, estimated by texture profile analysis, showed pressure-treated samples (400 MPa) to be harder than cooked (50 degrees C) or cooked and then pressure-treated or pressure-treated and then cooked samples, supporting the suggestion that pressure induces the formation of heat labile hydrogen-bonded structures while heat treatment gives rise to structures that are primarily stabilized by disulfide bonds and hydrophobic interactions. As expected, turkey myosin is more stable than that of cod; however, it seems their pressure-induced gelation mechanisms are similar.

Effect of muscle type, salt and pH on cooked meat haemoprotein formation in lamb and beef.

The rate of cooked meat haemoprotein formation, measured as the rate of loss of myoglobin solubility, in lamb was dependent on the muscles anatomical location and temperature. Lamb longissimus dorsi musle at 55 to 70°C formed cooked meat haemoprotein more rapidly than the muscles in the shoulder and leg. The formation in lamb was more rapid than in beef. The rate in high pH beef (7.25) l. dorsi was lower than found in beef l. dorsi of normal pH but in low pH lamb (5.38) l. dorsi the rate was, at most temperatures, also slower than found in this muscle from lamb of normal pH. In the presence of NaCl the rate of cooked meat haemoprotein formation was faster (almost doubled at 2g/100g meat) than found in the corresponding salt free lamb and beef samples. Other additives commonly added to meat products (mechanically recovered meat, oil, polyphosphates, soya, whey and caseinate) had little effect on the rate of cooked meat haemoprotein formation, at the levels normally used in meat products. It is concluded that for lamb products little if any myoglobin will remain soluble, and the products will look cooked before the recommended thermal treatment to inactivate Escherichia coli O157:H7 has been achieved. ©

Factors affecting the heat resistance of Escherichia coli O157:H7.

Escherichia coli O157:H7 has been reported as being not particularly heat resistant. However, several factors which might increase its heat resistance have been investigated in this study using five strains. Increase in growth temperature to 40 degrees C, as found in the cow gut, heat-shock at sub-lethal temperatures of 42, 45, 48 and 50 degrees C, and variable heating rate (1 degree C min-1 to 23 degrees C min-1) had no dramatic effect on heat resistance. Growth phase had a marked impact on heat resistance; late stationary phase cells were more heat-resistant than were log phase cells. The difference in heat resistance between the two phases of growth became more pronounced when cells were resuspended in fresh nutrient broth; heat resistance of late stationary phase cells increased dramatically whereas no such effect was observed with log phase cells. The addition of polyphosphates to the heating medium did not increase heat resistance. A reduction in water activity of the heating medium from 0.995 to levels between 0.980 and 0.960 also resulted in a marked increase in heat resistance. This effect was more pronounced under conditions of extremely low water activity created by resuspending late stationary phase cells in sunflower oil. Survivors were detected even after a heat treatment at 60 degrees C for 1 h or 70 degrees C for 5 min. It can be confirmed that this serotype has no unusual heat resistance and that the heating environment markedly affects resistance.

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.

Inhibition of metmyoglobin formation in fresh beef by pressure treatment.

Application of pressures of 80-100 MPa for 20 min improved the colour stability, as measured by rate of metmyoglobin formation, of longissimus dorsi and psoas major beef muscles exposed to air 2 days post-slaughter. However, pressure treatment of these muscles at 7-20 days post-slaughter did not improve their colour stability. It is suggested that pressure inhibits, at least partially, the mechanism(s) responsible for the low colour stability of very fresh beef.

High pressure effects on lipid oxidation in minced pork.

Washed muscle fibres and minced pork were subjected to high pressure treatment at 800 MPa for 20 min at 20 °C prior to storage at 4 °C. In both cases, high pressure treated samples oxidised more rapidly than the controls, as measured by 2-thiobarbituric (TBA) number. The rate of lipid oxidation of the high pressure treated samples was similar to that induced by heat (80 °C for 15 min). No significant increased rate of oxidation was observed in minced meat samples treated at 300 MPa but above this pressure the rate increased with intensity. Minced meat samples pressure treated in air had higher initial TBA numbers than those treated in nitrogen, but upon storage both oxidised more rapidly than untreated samples. Differential scanning calorimetry, reflectance spectrophotometry and electrophoresis showed that treatment above 300-400 MPa caused marked denaturation of the myofibrillar and sarcoplasmic proteins and conversion of reduced myoglobin/oxymyoglobin to the denatured ferric form. The possible role of these reactions in catalysing lipid oxidation is discussed.

Differential scanning calorimetry of lupin and soy proteins.

Differential scanning calorimetry (DSC) was used to study the 7S and 11S globulin fractions extracted from lupin seed (Lupinus luteus) flour. In agreement with previous work on other lupin species, the isolate showed three denaturation peaks compared to the two observed with soy. By comparison with the isolated globulin fractions, the denaturation peaks at the two higher temperatures in the lupin isolate were assigned to the 11S and 7S globulins. The denaturation temperature of the lupin 7S globulin was about 10 K higher than that for the corresponding soy globulin, whereas the values for the 11S globulin were similar. All globulins displayed increasing thermal stability with decreasing moisture contents. Possible reasons for the differences in behaviour of soy and lupin protein isolates are discussed.

Oxymyoglobin formation in meat and poultry.

The rate of oxymyoglobin formation (blooming) was estimated, by reflectance spectrophotometry and depth of oxygen penetration, of beef and pork 1. dorsi and chicken breast muscles of normal ultimate pH. Although beef bloomed very rapidly when exposed to air, even at 23°C, pork muscle exhibited little evidence of oxymyoglobin formation at this temperature and no chicken muscle produced oxymyoglobin at 23°C. Even after 48 h at 5°C there was little evidence of oxymyoglobin formation in the chicken muscles although formation was evident in the pork samples. After only 24 h storage at 5°C it was apparent that both the chicken and pork muscles oxidised to produce some metmyoglobin at their surface, though the amount produced was apparently more in the chicken than the pork samples. In most chicken samples held in air at 5°C the predominant pigments were the purple reduced myoglobin and brown metmyoglobin. The implication of these observations in relation to the packaging of chicken portions is discussed.

Characteristics of some intermediate moisture smoked meats.

Intermediate moisture smoked beef was prepared by cook-soak/equilibration in a solution containing sodium chloride, sodium nitrite and potassium sorbate. Two further solutions contained glycerol and glycerol + 'onion' in addition to the above ingredients. Half the samples in each treatment group were smoked for 18 h (heavy smoking) and the others for 4 h (light smoking) at 50°C. All samples developed the pink-red colour of nitrite cured meat but those treated with glycerol were darker, presumably due to decreased moisture contents. Glycerol increased the apparent moisture, fat and sodium dodecyl sulphate (SDS) soluble protein contents and also improved the conversion of haemoproteins to the cooked cured form but decreased the percent soluble hydroxyproline. Smoking caused a marked decrease in moisture, SDS-soluble protein and soluble hydroxyproline contents and slightly decreased the available lysine and percent conversion of the haemoproteins to the cured nitrose forms. Smoking also caused increased darkening and hardness of the samples. Total viable aerobes, coliforms and fungi were below the levels of detection while TBA values were low and all samples possessed no detectable rancidity. Electrophoretograms of the samples indicated that cooking/equilibration had no significant effects on the proteins present but smoking led to a slight loss of some of the protein components.

The stability of some intermediate moisture smoked meats during storage at 30°C and 38°C.

Intermediate moisture smoked beef was prepared by cook/soak equilibration in solution, with or without glycerol followed by smoking for 4 h or 18 h at 50°C. During storage for 12 weeks at 30 and 38°C all reactions except the change in pH were significatlyy slower at 30°C. This suggests that certain reactions; namely, hydroxyproline solubilization and protein crosslinking, have different temperature dependencies and opposing effects on pH. Heavy smoking and glycerol both reduce the rate of protein crosslinking, as measured by solubility in 3% sodium dodecyl sulphate + 1% ß-mercaptoethanol. Glycerol accelerates hydroxyproline breakdown but helps retain moisture, available lysine and tenderness. Heavy (18 h) smoking had a reverse effect on these reactions. Browning occurs in these products, as well as rapid pigment loss.