Joseph Culioli

Mechanical properties of meat

Determination of meat mechanical properties is still usually performed under empirical conditions, using tests which have been developed many years ago. This paper discusses the limitations of these methods. It also reviews recently developed research which has been focused on a more analytical approach to mechanical tests performed in closely controlled conditions. The objectives of these investigations are on the one hand to obtain specific properties of the myofibre and connective tissue structures involved in meat toughness and on the other hand to understand the fracture mechanisms involved in the perception of texture. Due to the anisotropic and composite nature of meat, attention has been focused on the influence of the direction and amplitude of strains to be used for the characterisation of myofibres and connective tissue, respectively. These strain conditions are linked to the contraction and stretching state of each of these structures. Indeed, whatever the type of deformation (shear, compression or tension), myofibre resistance can be determined under low strain conditions as long as collagen fibres in the connective tissue remain in a more crimped state than myofibres, i.e. in raw or slightly cooked meat of normal sarcomere length. On the contrary, determination of connective tissue resistance has, up to now, only been obtained using large strain tests. Contraction of collagen fibres induced by cooking makes the separate analysis of meat structures more difficult, but this can partially be overcome by applying mechanical tests in different strain directions. However, the role of the spatial distribution of connective network on the mechanical properties of meat still remains largely unknown. Image analysis and ultrasonic methods, currently developed to study this problem, are briefly presented.

Effects of high-intensity high-frequency ultrasound on ageing rate, ultrastructure and some physico-chemical properties of beef

High-intensity and high-frequency ultrasound was tested for its ability to accelerate meat ageing and increase beef tenderness. Samples (≈50g) of semimembranosus muscles from 8 cull cows were assigned to ultrasonic treatment (2.6MHz; 10W/cm(2); 2 ×15s) either pre-rigor (day 0, pH 6.2) or post-rigor (day 1, pH 5.4). When applied pre-rigor, ultrasound induced a slight delay in rigor mortis onset, a stretching (12-15%) of the sarcomeres (p<0.05), an ultrastructural alteration in the Z-line region and an immediate increase (around 30%) in the release of calcium in the cytosol (p<0.05). However, no conclusive effect on meat ageing rate was observed. Post-rigor ultrasonic treatment did not induce any structural modification but slightly improved the ageing index after 6 days (p<0.05). However, no improvement in the final (day 14) ageing index was observed compared to the controls. As ultrasound had also no effect on the thermal stability of collagen, at both postmortem times, no improvement in meat tenderness can be expected under the conditions used.

Application of texture image analysis for the classification of bovine meat

Texture analysis has been used to classify photographic images of meat slices. Among the multiple muscular tissue characteristics that influence meat quality, the connective tissue content and spatial distribution, which define the grain of meat, are of great importance because they are directly related to its tenderness. Connective tissue contains two important components, fat and collagen, which are variable with muscles, breed and also with age. These components are clearly visible on photographic images. Fat and collagen are particularly emphasised by ultraviolet light. The meat slices analysed came from 26 animals raised at INRA of Theix by the LCMH Laboratory. Three different muscles were selected and cut off from carcasses of animals of different breeds and of different ages. The biological factors (muscle type, age and breed) directly influence the structure and composition of the muscle samples. The image analysis led to a representation of each meat sample with a 58 features vector. Classification experiments were performed to identify the samples according to the three variation factors. This study shows the potential of image analysis for meat sample recognition. The correlation of the textural features with chemical and mechanical parameters measured on the meat samples was also examined. Regression experiments showed that textural features have potential to indicate meat characteristics.

Perimysial collagen crosslinking and meat tenderness in Belgian Blue double-muscled cattle

The relationship between intramuscular collagen and five collagen crosslink concentrations, and the tenderness of meat from Belgian Blue normal, heterozygous double-muscled (DM) and homozygous DM cattle was investigated using M. semitendinosus (St) and M. gluteobiceps (Gb). The histidinohydroxymerodesmosine (HHMD) concentration (per mol collagen) in St was less in DM animals than normal animals. Concentrations (per gram of wet meat) of HHMD and Erlich chromogen (EC) in Gb, and HHMD, EC, dihydroxylysinorleucine (DHLNL) and hydroxylysinorleucine (HLNL) in St were also lower in DM animals than normal animals. Shear force of raw meat was significantly greater in normal animals than DM for both muscles; cooked meat shear force was greater in the normal animals for the Gb muscles only, showing a good correlation with sarcomere length. Most correlations between shear force and collagen or crosslink concentrations were not significant and those that were highly significant were generally weak.

Effect of pelvic suspension and cooking temperature on the tenderness of electrically stimulated and aged beef, assessed with shear and compression tests.

Electrically stimulated carcass sides of young bulls were suspended at 1 hr post mortem from the aitch bone (pelvic suspension; PS) and Achilles tendon (AT), respectively. After an ageing period of 14 days at 3 °C, shear force (SF) and compression (20 and 80% compression) tests of the Mm. longissimus lumborum et thoracis (LO) and semimembranosus (SM) were conducted in raw muscle and after heating for 1 hr at 55, 60, 65, 70 and 80 °C. Collagen content was higher in SM than in LO, while sarcomere length (SL) of raw muscle were 1.75 and 1.78, for LO and SM. In comparison with the AT-side, PS increased SL by 21 and 47% and cooking loss (at 80 °C) by 2 and 6% for LO and SM, respectively. Drip loss of whole muscles from the PS-side during the ageing period tended to be lower (n.s.). Over the whole cooking temperature range, SF-values were relatively high for the SM in comparison with LO. For both muscles from the AT-side, the lowest SF-values were observed at 60 and 65 °C. The PS-treatment resulted in higher SF- values for raw muscle and after cooking at low temperatures (55 and 60 °C), particularly in the SM. In the intermediate temperature range (65 and 70 °C), PS had no significant effect, while in the higher temperature range (80 °C), SF-values were lower in the PS-side. Similar tendencies were observed in the LO, although the lower SF-values for the PS-side were observed already at 60 °C. In non-destructive compression (20%), there was a gradual increase in stress values with increasing cooking temperature. In comparison with the AT-side, the PS treatment resulted in the LO in similar or higher, and in the SM in lower stress values. With destructive compression (80%), PS resulted in SM in higher stress values in raw muscle and at 55 °C, in accordance with the SF-values. It is suggested that the higher SF- and 80% compression values in raw muscle and at low cooking temperatures, are caused by an increase in collagen strength due to a change in the direction and spatial organisation of the collagen fibres as a result of stretching of the muscle. This study demonstrates that the relative contributions of the collagen and myofibrillar components to the mechanical assessed toughness, as well as the effect of pelvic suspension, is dependent of muscle, cooking temperature and the mechanical test applied.

Determination of Surface Hydrophobicity of Fast and Slow Myosins from Rabbit Skeletal Muscles: Implication in Heat‐Induced Gelation

Both aliphatic and aromatic surface hydrophobicities of myosins from fast-twitch psoas major and slow-twitch semimembranosus proprius muscles were investigated using fluorescence probes (cis-parinaric acid and 8-analino-1-naphthalene sulphonic acid). Surface hydrophobicity of unheated slow myosin was 1.5-fold higher than that of fast myosin. However, heating led to an increased enhancement of fast myosin hydrophobicity which became, after heating, higher than that exhibited by heated slow myosin. Whatever the myosin isoforms, most surface hydrophobicity was on the myosin heads. Heating induced a rise in hydrophobicity of the S1-subfragment from slow and fast myosins. However, the hydrophobicity of rods from fast myosin was increased three-fold more by heating than did that from slow myosin. Finally, the blocking of hydrophobic binding sites affected differently the heat-induced gelation in high ionic strength (0.6 M KCl) of both myosin isoforms and confirmed that the molecular mechanisms involved in the gelation were muscle-type dependent.

Performance, muscle composition and meat texture in veal calves administered a β-agonist (Clenbuterol)

The effect of clenbuterol administration on performance, muscle composition and meat texture was studied in veal calves. Three groups, of ten animals each, were assigned to the three following treatments for 27 days: control, administration of 0·3 and 1·0 ppm in the feed (dry matter basis). After a 14-day withdrawal period, the animals were slaughtered, and three muscles were sampled (M. longissumus thoracis; M. triceps brachii caput longum; M. rectus abdominis). During the period of clenbuterol administration, the treated calves exhibited a higher daily liveweight gain (DLWG) and a higher feed conversion efficiency (FCE) compared to those of the control calves, but these effects were reversed during the subsequent withdrawal period. At slaughter, the overall DLWG, FCE and carcass weight were similar in the three treatments, but the dressing percentage in the clenbuterol-treated calves was up to 5·7 points higher than that of the control calves. In the muscles studied, the clenbuterol had little effect on pH, sarcomere length, dry matter and nitrogen contents, collagen heat stability (solubility, isometric tension) or cooking loss; but it markedly reduced the content of lipids, collagen and haem pigments. The clenbuterol also affected myofibrillar strength after ageing, measured either on raw meat or on cooked meat. This was particularly evident in cooked meat which showed up to a two-fold increase in mechanical parameters (maximum stress, compression modulus) after the clenbuterol treatment. No dose effect was detected except for the mechanical parameters. It was concluded that clenbuterol administration affects, meat in two opposite ways, viz. a marked toughening effects, due to a reduction in the muscle ageing rate, that is not compensated by a concomitant tenderizing effect (through a decrease in the intramuscular collagen content).

Influence of technological parameters on the structure of the batter and the texture of frankfurter type sausages

The aim of the study was, on the one hand, to determine the relationships between various technological factors, the structure of the batters and the texture characteristics of frankfurter type sausages, and, on the other, to define the possibilities of realizing a reference scale for texture. The addition of sodium chloride in the 0-2% range induces a large increase (60%) in the cooking yield, a decrease in the specific gravity and an increase in the viscosity of the batter determined indirectly through the evolution of the product temperature during chopping. These variations together, give a 30% decrease in the mechanical firmness and a 100% and 90% increase in the juiciness and elasticity of the final products, respectively. However, beyond 2%, sodium chloride does not induce any significant effect on these characteristics. The addition of caseinate in a 1-3% range induces a degassing of the batter and a 10-37% decrease in the water losses during cooking. The higher the caseinate content in the 0-6% range, the larger the rise in the batter temperature during chopping. Sausages are also considered harder (+22%) and less juicy and elastic (-50%) when caseinate content increases. Addition of 0·1-0·5% polyphosphates and chopping under vacuum (0·2 atm) induce variations in the cooking yield, +3% and -1%, respectively, but have no influence on the texture of the final products. Modifications of all these technological parameters induced variations by a factor of 2 in the different mechanical parameters and in parallel differences of 1-2 points on a 6 point scale for sensory characteristics.

Meat bolus properties in relation with meat texture and chewing context

During chewing the meat sample is fragmented by compressive and shear bite forces while saliva is incorporated. At the end of this process meat is transformed into a bolus with specific properties, which elicit deglutition. This study aims to analyze the mechanical properties of the boli and juice-saliva interactions in different chewing contexts. Two groups of subjects with different chewing efficiencies participated in the study: healthy dentate (n=9) and denture wearers (n=7). Meat boli were obtained from two beef samples exhibiting different textures obtained by varying aging time and cooking temperature. Variables linked to saliva-food matrix interactions (boli volume and weight, dry matter content) were not dependent on muscle fiber disorganization evaluated using shear tests. No texture effect was observed from the mechanical properties of the boli, whatever the chewing context. Denture wearers swallowed less disorganized boli but with a similar water content as dentate. Between subjects variability was the highest for saliva-food interactions and the lowest for mechanical properties. The variations obtained in meat boli characteristics could have consequences on sensory properties perception and on the digestion process.

Effects of muscle texture on ultrasonic measurements

In this study bovine muscle samples were analysed using an ultrasonic method to investigate the influence of compositional and textural characteristics on ultrasonic measurements. The ultrasonic method was based on the measurement of acoustic parameters (velocity, attenuation and backscattering intensity) which are closely related to physical properties of the propagating medium. An examination of physical parameters was proposed by two types of representations: a mean profile and a parametric image. Two muscle types, which differ in composition and structure were studied. On the same samples additional measurements, mechanical resistance and chemical composition, were performed and used to show the influence of meat composition and texture on ultrasonic data.