Antimicrobial effects of selected plant essential oils on the growth of a Pseudomonas putida strain isolated from meat

Dielectric properties of beef biceps femoris muscle were recorded during heating (5-85°C) to assess their linkage to phase changes monitored by differential scanning calorimetry (DSC) and rheology. DSC indicated endotherms between 56 and 81°C corresponding to denaturation of actin, collagen and myosin. Matching changes in dielectric properties (dielectric constant (ε') and loss factor (ε″)) were noted at radio and/or microwave frequencies though the nature of the change differed depending upon frequency. The main observation in ε' was an increase above 65-66°C, most likely due to fluid release on collagen denaturation. This fluid plus liquid from myosin denaturation most likely solvated ions freed during myosin denaturation which manifested as an ε″ increase. However, it must be noted that meat structural protein denaturation is compounded with physical shrinkage which can also influence dielectric properties. Rheological parameters of beef muscle heated from 5 to 85°C also displayed marked changes relating to structural protein denaturation.     

Effect of cooking temperature on the percentage colour formation, nitrite decomposition and sarcoplasmic protein denaturation in processed meat products

The effect of cooking temperature and time on the percentage colour formation, nitrite decomposition and denaturation of sarcoplasmic proteins in processed meat products was investigated in detail. The colour forming percentage increased with a rise in temperature of heating, especially at 50-60°C (P < 0·05). The percentage nitrite decomposition was promoted by the retention time of cooking rather than by the cooking temperature (P < 0·05). The percentage of sarcoplasmic proteins denatured was enhanced by heating temperature in the range 50-80°C (especially at 50-60°C) (P < 0·05). The relationship between the percentage colour formation and the percentage of sarcoplasmic proteins denatured is discussed. The SDS-PAGE patterns of the heat-treated samples revealed the components of the sarcoplasmic proteins which had been denatured.     

Modelling the effect of sarcomere length on collagen thermal shortening in cooked meat: consequence on meat toughness

Normal and contracted pieces of Semimembranosus and Longissimus Dorsi muscles from cull cows were cooked for 90 min at temperatures up to 80°C. For both muscles, at 50°C the normal samples have higher breaking stress than contracted samples. The breaking stress of normal samples decreases at 55°C. This decrease is not observed for contracted samples. The contracted samples become the tougher above 60°C. Drip and cooking losses are the highest in contracted samples. Sarcomere length decreases above 60°C whatever the raw sarcomere length. The amplitude of thermal shortening of perimysium collagen fibres in cooked meat has been calculated. This theoretical model takes into account the changes in the waviness of collagen fibres associated with changes in raw sarcomere length and the geometrical changes of fibre bundles due to drip, cooking losses and cooking shortening. The calculations lead to the conclusion that thermal shortening of collagen fibres at 60°C is lower in contracted samples than in normal samples. As the final modulus of collagen fibres decreases when their thermal shortening increases, this can explain part of the differences observed between the toughness of normal and contracted cooked meats. In particular, it can explain why contracted cooked meat becomes tougher than normal meat just above 60°C and why there is a decrease in normal meat toughness between 55 and 60°C. This work therefore emphasises the role of collagen in toughening associated with cold shortening.     

Improved protein recovery from some meat industry by-products

The proportion of protein recoverable from bovine heart, kidney, liver, lung, rumen and spleen by alkaline extraction, followed by reacidification, was found to be related to the temperature of extraction, the recovery of both lung and rumen protein at 60°C being approximately twice that at 0°C. Extraction for more than 2 h gave increases in protein recovery. The increased protein solubility was partly due to increased solubilisation of collagen and to a reduction in the quantity of protein precipitated by acidification. Alkaline extraction of lung and rumen at 60°C resulted in the formation of the dipeptide lysinoalanine (0·39 and 0·49 g/16gN, respectively), with tracev amounts at 20°C and 40°C. The electrophoretic patterns of raw meat industry by-products are discussed in the light of previous findings.     

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.     

The effect of cooking temperature on mechanical properties of whole meat, single muscle fibres and perimysial connective tissue

The structural changes in beef semitendinosus caused by cooking were studied by performing tensile tests of the isolated meat components (i.e. single muscle fibres and perimysial connective tissue) and related to the toughness of the whole meat. Whole meat toughness was found to increase in two separate phases upon cooking from 40-50°C, and again from 60 to 80°C with a decrease in meat toughness between 50 and 60°C, in agreement with previous studies. The changes in whole meat toughness at temperatures below 60°C were found to correspond to changes in the mechanical properties of the perimysial connective tissue, whereas changes of whole meat toughness at temperatures above 60°C were found to correspond to increased breaking strength of single muscle fibres. The myofibrillar component explained approximately 47% of the variation in whole meat toughness upon cooking whereas inclusion of the connective tissue component increased the goodness of fit.     

Effect of cooking temperature and time on the physico-chemical, histological and sensory properties of female carabeef (buffalo) meat

The effect of cooking temperature (80-100°C) and time (30-60min) on collagen solubility of Semimembranosus muscle in carabeef were investigated. The pH, cooking loss, shear force value, collagen content, collagen solubility, sensory evaluation and histological observations of water bath cooked and pressure cooked Semimembranosus meat samples were measured. Increase in pH, cooking loss, collagen solubility and tenderness scores with decrease in shear force value and collagen content was observed with increases in cooking temperature and time. However, no statistical difference was observed for shear force values, collagen solubility values and tenderness scores in pressure cooked meat and meat cooked in a water bath at 100°C for 45min, inferring that cooking of buffalo meat at 100°C for 45min improved collagen solubility and tenderness to the same extent as that due to pressure cooking.     

Effect of post-slaughter processing and freezing on the functionality of hot-boned meat from young bull

The effects of variation in the times of mincing post mortem (2, 4, or 6 h), pre-rigor salting (1.5% wt wt ) and freezing rate [fast (10 min, liquid nitrogen); medium (4-6 h at -40 °C and 0.8 m s(-1) air velocity); or slow (36-38 h at -10 °C and 0.1 m s(-1) air velocity followed by 12 h at -20 °C and 0.1 m s(-1) air velocity)] on the functionality of young bull meat were examined using hot-boned forequarters. At 52 h post packaging, the meat was thawed (72 h at 4 °C), its pH measured, and it was used to make finely comminuted batters. Cook yield and stress and strain of the cooked batters were measured. Time of mincing had no effect on meat pH, cook yield or stress and strain. There was a significant interaction (P < 0.05) between pre-rigor salting and freezing rate for pH. Freezing rate did not affect the pH of pre-rigor salted meat whereas the pH of unsalted pre-rigor meat was highest at the fastest freezing rate. Meat salted pre-rigor had a significantly (P < 0.05) higher pH than the post-rigor chilled control. Pre-rigor salting decreased the stress values of cooked batter whereas the slowest freezing rate increased stress. Stress and strain values for cooked batters from thawed meat were not significantly different from the values for batters made from the unfrozen control. Cook yields of batters made from pre-rigor frozen meat were higher than that of the postrigor control but not significantly so. The results indicate that suppliers can use pre-rigor salted and frozen meat when manufacturing comminuted products without major detrimental effects on the cook yield and texture of the finished product.     

Breakdown of connectin during cooking of meat

Light-scattering studies on extracts of meat have confirmed the heat-induced breakdown of connectin previously observed by SDS gel electrophoresis. Because of the high subunit MW (～10(6)) of connectin, the weight-average molecular weight of whole muscle undergoes a relatively large decrease when connectin is broken down during heating of meat. In cold-shortened muscle, breakdown of connectin by proteolysis was as rapid as in control samples, suggesting that connectin exists in an exposed environment rather than as a core to thick filaments. The breakdown of connectin during heating at 60 or 80°C for 40 min was more extensive than during ageing for 3 weeks at 2°C. Hence, the partial proteolysis of connectin during storage at 2°C is unlikely to be responsible for tenderisation induced by ageing.     

Effects of electrical stimulation, boning-temperature and conditioning mode on display colour of beef meat

The effects of electrical stimulation of hot-boned (ESHB) bovine longissimus dorsi muscle, followed by vacuum packaging with different temperature/time regimes and storage in aerobic conditions, compared with cold-boned treatment (CB), on colour characteristics was assessed. No significant difference in haeminic iron content was noted between ESHB and CB meat. The opacity was more pronounced in ESHB meat vacuum packaged and incubated at 37°C. This treatment (37° C/4 h) allowed a lighter and brighter red meat colour with a higher level of contamination which was always acceptable. The worst results for colour characteristics were obtained with ESHB meat conditioned rapidly at 2°C. No differences were noted between ESHB meat conditioned at 25°C and CB meat. To explain these discrepancies between treatments about colour characteristics, where muscle translucency is largely involved, differences in enzymic reducing activity and denaturation of sarcoplasmic proteins during glycolysis must be implicated.     

Heat and ultrafiltration extraction of broiler meat carnosine and its antioxidant activity

This study examined the effects of extraction and further ultrafiltration on the carnosine content, antioxidant activity and total iron content of chicken muscle extracts. Fresh breast meat had 7-fold higher carnosine than fresh thigh meat (2900 versus 419μg/g meat, respectively). Carnosine extracts of breast and thigh were prepared by heating at 60, 80 and 100°C, and ultrafiltration (UF) using a 5000MW cut-off. At increasing temperatures, protein concentrations decreased while carnosine, total iron and antioxidant activity increased. Antioxidant abilities of the 80 and 100°C-heated extracts were greater than that of the 60°C extract (p<0.05). The ultrafiltrate from the 80°C-heated extract had approximately 20% higher carnosine, but 40% lower protein and 10-30% lower iron than the 80°C-heated ultrafiltrate. However, compared in terms of carnosine concentration, the meat extracts had greater antioxidant activity than pure carnosine (p<0.05).     

The effect of conditioning on the strength of perimysial connective tissue dissected from cooked meat

Tensile tests were carried out on ribbons of perimysial connective tissue dissected from slices of bovine semitendinosus muscles that had been conditioned or not conditioned and then cooked to a range of temperatures. A consistent reduction in the strength of the perimysia was seen in the conditioned samples, both in the raw meat and meat cooked to 50°C. At higher cooking temperatures (60-80°C), no effect of conditioning was seen. The content of collagen or total protein of mechanically extracted perimysia and the collagen content of the test pieces from conditioned and unconditioned muscles was not significantly different. It was concluded that conditioning decreases the breaking strength of the perimysial connective tissue in raw meat or in meat which is subsequently cooked to 50°C, but not in meat cooked to the temperatures normally employed by consumers. The tenderization observed in conditioned meat cooked to 60°C and above is, therefore, due to the weakening of muscle fibres within the fibre bundles.     

Extended shelf-life of unrefrigerated prerigor cooked meat

Five experiments were conducted to evaluate the microbial quality of unrefrigerated cooked prerigor beef after the application of oxygen-permeable packaging. Specific objectives were to combine the beneficial effects of aerobic packaging, meat surface acidification and prerigor rapid cooking rates on meat storage stability at ambient temperature. In the experiments, the triceps brachii muscle was dissected from one side 45 min after exanguination of the animal, and samples of 2 × 3 × 5 cm were prepared. Bags made of a strong barrier, plastic film, and a highly oxygen permeable oriented polypropylene, were used. The cooking of the packaged samples covered a number of treatments ranging from cooking in a 70°C water bath to an internal sample temperature of 65°C to cooking in 100°C water for 40 min. Reheating and multiple heat treatments were also included. The pH values of the cooked samples were determined and aerobic plate counts (log(10)/g) were determined for the cooked samples at various intervals during two weeks of storage at 22°C or at 3°C for the control samples. The results indicate that heat treatment alone did not improve shelf stability at 22°C. However, dipping the samples in 80°C solutions of 0·7% citric acid or 1·25% lactic acid for 1 min and draining for 1 min followed by packaging using oxygen permeable bags and cooking in 100°C water for 40 min consistently resulted in shelf stable products at all 22°C storage intervals. The lactic acid treatment was superior to the citric acid treatment because it completely decontaminated the samples and delayed spoilage, especially at 3°C.     

NMR relaxometry and differential scanning calorimetry during meat cooking

By combining simultaneous nuclear magnetic resonance (NMR) T₂ relaxometry and differential scanning calorimetry (DSC) on pork samples heated to nine temperature levels between 25 and 75 °C, the present study investigates the relationship between thermal denaturation of meat proteins and heat-induced changes in water characteristics. Principal component analysis (PCA) on the distributed ¹H NMR T₂ relaxation data revealed that the major changes in water characteristics during heating occur between 40 and 50 °C. This is probably initiated by denaturation of myosin heads, which however, could not be detected in the DSC thermograms obtained directly on the meat. In contrast, the DSC thermograms revealed endothermic transitions at 54, 65 and 77 °C, probably reflecting the denaturation of myosin (rods and light chain), sarcoplasmic proteins together with collagen and actin, respectively. Simultaneous modelling of DSC and NMR data by partial least squares regression (PLSR) revealed a correlation between denaturation of myosin rods and light chains at 53–58 °C and heat-induced changes in myofibrillar water (T₂ relaxation time 10–60 ms) as well as between actin denaturation at 80–82 °C and expulsion of water from the meat. Accordingly, the present study demonstrates a direct relationship between thermal denaturation of specific proteins/protein structures and heat-induced changes in water mobility during heating of pork.     

Effects of salt reduction on the rheological and gelation properties of beef, pork and poultry meat batters

The gelation and rheological properties of beef, pork and poultry meat batters as affected by salt reduction (2·50, 1·25 and 0·00%) were studied by using a Haake rotational viscometer and a thermal scanning rigidity monitor. Beef batters showed a decrease in shear stress with the decrease in salt levels at both high and low shear rates. Pork batter showed a mixed behavior (no definite trend in shear stress versus shear rate) and the poultry meat batters showed a Bingham pseudoplastic behavior, except for the no-salt treatment. During heating the beef batters showed the highest G values followed by the pork and the poultry meat batters. The rigidity modulus profiles exhibited two major transition temperatures at 47-53°C and at 64-76°C. Beef batter with 2·50% salt developed the highest average G value (16·6 kPa) and the poultry batter with 2·50% salt the lowest (7·3 kPa).     

Collagen contribution to meat toughness: Theoretical aspects

One of the major changes in connective tissues during heating is the transformation of the quasi-crystalline structure of collagen into a random-like structure. This molecular change induces a shortening of these tissues and gives them a rubber-like behaviour. In this state, their mechanical properties are dependent on the total number of cross-linked chains present per volume, which can be estimated from the number and the functionality of each cross-link present in the sample. The number of cross-linked chains per volume of meat explains a large amount of the tenderness variation, produced by muscle type, animal age, type, and sex in different species. During heating collagen fibres and fibrils shortening produces a pressure which is also dependent on the total amount of cross-linked chains present per volume, but also on the morphology of endomysial and perimysial envelopes. In meat, during heating, collagen fibres and fibrils thermal shortening is restricted by muscle fibres and muscle fibre bundles. This restriction, which depends on several muscle fibre characteristics, has a strong effect on the final elastic modulus of connective tissues, by changing the respective amount of crystalline and rubber-like fractions in collagen fibres and fibrils after heating. The implications of this phenomenon in tenderness variations are discussed.     

Collagen contribution to meat toughness: Theoretical aspects

One of the major changes in connective tissues during heating is the transformation of the quasi-crystalline structure of collagen into a random-like structure. This molecular change induces a shortening of these tissues and gives them a rubber-like behaviour. In this state, their mechanical properties are dependent on the total number of cross-linked chains present per volume, which can be estimated from the number and the functionality of each cross-link present in the sample. The number of cross-linked chains per volume of meat explains a large amount of the tenderness variation, produced by muscle type, animal age, type, and sex in different species. During heating collagen fibres and fibrils shortening produces a pressure which is also dependent on the total amount of cross-linked chains present per volume, but also on the morphology of endomysial and perimysial envelopes. In meat, during heating, collagen fibres and fibrils thermal shortening is restricted by muscle fibres and muscle fibre bundles. This restriction, which depends on several muscle fibre characteristics, has a strong effect on the final elastic modulus of connective tissues, by changing the respective amount of crystalline and rubber-like fractions in collagen fibres and fibrils after heating. The implications of this phenomenon in tenderness variations are discussed.     

Hydrolysis of the sarcoplasmic, myofibrillar and connective tissue proteins of lean beef by alcalase and its relationship to whole meat hydrolysis

The enzymic hydrolysis and solubilisation of the three meat protein fractions have been investigated in order to elucidate some aspects of the hydrolysis of whole beef protein. Much of the water-soluble sarcoplasmic protein fraction was insolubilised on heating for 25 min at 60°C. While most of this insoluble protein was easily resolubilised enzymically, some of it remained insoluble after 5 hours' hydrolysis. Solubilisation of connective tissue by Alcalase after a 3 h reaction increased markedly from 23% at 55°C to 99% at 60°C. This explains the high optimum temperature for solubilisation of whole beef by Alcalase. A significant portion of myofibrillar tissue remained insoluble after 3 hours' reaction. indicating that the majority of the insoluble solids remaining after whole meat hydrolysis at 60°C derived from myofibrillar tissue. There was good agreement between an experimental reaction progress curve for whole beef hydrolysis and one estimated from progress curves for hydrolysis of the three meat protein fractions.     

Comparison of various types of starch when used in meat sausages

Technological and sensory properties of meat sausages formulated with 4·0% of either potato flour, modified (acetylated distarch phosphate) potato starch, wheat, corn or tapioca starch were compared. Sausages were analyzed after cooking at temperatures between 65 and 85°C followed by storage at 5°C and -25°C. Characteristics evaluated were weight loss during cooking and storage, instrumentally and sensory assessed firmness, taste and smell of sausages. The results revealed differences in the suitability of starches for use in meat sausages. Part of the differences could be ascribed to differences in gelatination properties of the starches. With the criteria used for evaluating quality, potato flour was rated as the best suited starch followed by wheat starch while tapioca was rated as the least suited. Corn starch required cooking temperatures above 75°C and showed relatively low freeze/thaw stability. The modified potato starch stored well both above and below the freezing point.     

Kinetic migration studies from packaging films into meat products

One of the main concerns regarding safety of food packaging is the possible migration of chemical substances (monomers and other starting substances, additives, residues) from food contact materials into foods. To evaluate the effect of the fat content and of the temperature of storage on the migration from plastics packaging films into meat products as an important class of foodstuffs, the kinetic mass transport of a model migrant (diphenylbutadiene) from low density polyethylene (LDPE) film in contact with different meat products was investigated. From the data, the diffusion coefficients were calculated for the applied test conditions, by use of a mathematical model. The results showed that migration increased with fat content and storage temperature. Analysis of migration data corresponding to minced pork meat containing different amounts of fat, stored for 10 days at 25°C, revealed an excellent relationship between migration level and fat content. This behaviour was also found for other types of meat products (chicken and pork neck). A simplifying mathematical model was applied to derive effective diffusion coefficients in the polymer which, however, do take kinetic effects in the meat also into account. In the case of pork meat contact, the effective diffusion coefficients derived from mathematical modelling were ten times higher for storage at 25°C (1.88×10(-9)cm(2)s(-1)) than for storage at 5°C (1.2×10(-10)cm(2)s(-1)).