Effects of ageing and cooking on the tenderness of beef muscle

When beef sternomandibularis muscle was subjected to prolonged cooking, toughness, measured by shearing force across the grain, was reduced by about 50%. The shortened state of the muscle determined the final shear-force value attained as in normal cooking, being considerably higher in meat at 40% shortening, than in either unshortened meat or in meat shortened by 60%. The tenderising effect of ageing was additional to that from long cooking. Ageing reduced the tensile strength of the myofibrils as measured by resistance to the shearing stresses of homogenisation. Cooking tenderising resulted from a breakdown in the collagen of the interstitial connective tissue. In cooked meat distinct linkages were shown to exist between Z-lines of adjacent myofibrils. The mechanical strength of cooked meat is ascribed to the tensile strength of the fibrous components of muscle and these lateral linkages.     

Muscle fiber properties and thermal stability of intramuscular connective tissue in porcine M. semimembranosus

BACKGROUND: Strips can be easily peeled from raw destructured pork (M. semimembranosus, SM muscle) by hand but in normal meat these strips break. In general, destructured meat is pale in color. Porcine SM muscles have thick muscle fibers which could predispose them to destructuration. This study investigated whether the onset and peak temperatures of thermal shrinkage (T_o and T_p) of intramuscular connective tissue from SM muscles were associated with muscle fiber thickness, capillary density or extracellular space. We also investigated whether these muscle fiber properties of destructured muscles differed from those of normal muscles. RESULTS: The destructured and normal muscles were similar in muscle fiber cross‐sectional area, capillary density, extracellular space and sarcomere length. T_o correlated negatively with sarcomere length. The water content of differential scanning calorimetry samples consisting of intramuscular connective tissue was higher in destructured muscles than in normal muscles. CONCLUSION: Muscle fiber properties (muscle fiber cross‐sectional area and sarcomere length) and capillary density are similar in destructured and normal SM muscles. T_o and T_p of intramuscular connective tissue are similar in destructured and normal muscles. Muscle fiber properties show no association with the thermal shrinkage properties of intramuscular connective tissue. Copyright © 2009 Society of Chemical Industry     

PREDICTING MEAT TENDERNESS FROM MUSCLE TENSILE PROPERTIES

Two major types of objective measurements were performed on raw porcine psoas muscle (I - shearing and breaking strength tests; II - sarcomere length, elasticity, stress relaxation and break elongation) and compared with taste panel evaluation (tenderness, elasticity, and chew count) of cooked meat. A standard sample of texturized vegetable protein used as a reference by the panel proved useful in reducing variations between the chew count test and the objective evaluation; it was not of significant value with the other sensory evaluations. No significant correlations were found between the two groups of objective measurements. Breaking strengths of small longitudinal strips of tissue, following a brief cyclic or extension stretching on the Instron, were the best predictors of sensory tenderness accounting for 59–90% of variation. Other measurements also gave significant correlations. The major source of variation in breaking strength values was the variation between animals, but the post-mortem treatment (restraining versus not restraining during rigor) and the interaction between animals and the post-mortem treatment also were significant in some cases. Breaking strengths of uncooked samples from the same muscle showed a coefficient of variation of up to 54%. It is concluded that there are two major structural contributions of raw muscle to cooked meat tenderness, a connective tissue factor and a contraction factor; different objective methods are best suited for their evaluation.     

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.     

ACETIC ACID MARINADING—THE RHEOLOGICAL CHARACTERISTICS OF SOME RAW AND COOKED BEEF MUSCLES WHICH CONTRIBUTE TO CHANGES IN MEAT TENDERNESS

The tensile and adhesive characteristics of acetic acid marinaded bovine Ms sternomandibularis (StM), infraspinatus (IS), triceps brachii caput longum (TB), and psoas major (PM) were studied over the meat pH range 5.80 to 4.10 on both raw and cooked strips of muscle. In the raw muscle samples, tensile and adhesive characteristics were greatest around pH 5.0, progressively decreasing as muscle pH values approached 4.1. Cooking increased tensile strength, particularly around pH 5.0 where peak force values virtually doubled. Cooking had less influence on the adhesive characteristics of all muscle samples which tended to decrease below pH 4.5. In both raw and cooked muscle samples, intermuscular differences in adhesive characteristics were also much greater than those obtained for tensile characteristics. Irrespective of intermuscular differences in collagen content or its degree of maturity, the gradual decreases in tensile and adhesive characteristics below pH 5.0 could be related to the effect of acetic acid induced swelling on both muscle fibres and the connective tissue network. The influence of acetic acid marinading in promoting meat tenderness is due more to its effect on the behaviour of the muscle fibres during cooking than to its effect on the connective tissue network of different muscles.     

Mechanical and structural characteristics of single muscle fibres and fibre groups from raw and cooked pork longissimus muscle

The aim of this study was to analyse the mechanisms that determine why small groups of muscle fibres may have different mechanical properties than single muscle fibres. The method used combined light microscopy and tensile testing on single fibres and small groups of fibres from raw and cooked (80 °C) meat, from both conditioned and unconditioned porcine longissimus muscle. The results showed that small groups of fibres had different breaking properties than constituent single fibres in raw muscle, but that these differences diminished on cooking. Raw groups of fibres showed a more uniform lengthening along their entire length and a higher extension to rupture than single fibres. Conditioning increased maximum strains in both single fibres and small fibre groups. In unconditioned cooked meat, single fibres and fibre groups showed comparable breaking stresses and extensions. Conditioning resulted in a lower strength in fibre groups than in single fibres. These results show that (endomysial) connective tissue linkages between adjacent muscle fibres in a small group significantly alter the breaking behaviour of single fibres. The effects of these connective tissue linkages are not reduced by conditioning alone, but are largely diminished by cooking to 80 °C.     

POSSIBLE RELATIONSHIPS BETWEEN SHEAR, TENSILE, AND ADHESION PROPERTIES OF MEAT AND MEAT STRUCTURE

Contributions to the structural strength of meat samples by the myofibrillar and connective tissue components were altered by varying the myofibrillar contraction state, muscle type and the cooking temperature. Shear, tensile and adhesion measurements were used to evaluate quantitatively changes in the properties of the samples. Detailed examination of shear and tensile force-deformation curves suggested that the initial effect of shear, compression or tensile force was to produce a yield in the myofibrillar structure. After the initial yield, the applied force was probably resisted mainly by the connective tissue structure. Adhesion and tensile values showed changes which indicated a probable rearrangement of the collagen fibers in the connective tissue network as it adjusted to accommodate changes in the myofibrillar contraction state.     

Collagen Content and Subjective Scores for Tenderness of Connective Tissue in Animals of Different Ages

SUMMARY— Collagen nitrogen in raw steaks was related to subjective scores for tenderness of connective tissue in steaks cooked to 61° from two muscles, L. dorsi and B. femoris from three groups, veal, baby beef, and mature beef, of eight animals each. A highly significant, but somewhat low correlation, −0.54, indicated that collagen in raw meat would be an index of the tenderness of connective tissue within cooked meat. Correlations within muscle groups indicated a better index in the B. femoris . The amount of collagen nitro, gen was not different between the age groups. Panel scores within B. femoris were indicative of larger amounts and tougher connective tissue in the older animals.     

THE EFFECTS OF LONG TERM COOKING ON SHEAR FORCE-DEFORMATION CURVES

The influence of muscle contraction, pressure-heat, and cooking conditions on some parameters of the Warner Bratzler shear force curves were studied. Stretched meat samples, restrained from shortening along the muscle fibers during cooking for a short time at 90°C, had larger peak shear force values than samples cooked unrestrained. As cooking times were increased, peak shear force values decreased until after 8-16 hr the cooked restrained samples had lower values than the unrestrained ones. The initial yield force values obtained for pressure-heat treated samples were not significantly affected by cooking at 90° for up to 32 hr, although the peak shear force values decreased with cooking time. The experimentally determined shear curves were shown to be approximated by summing the estimated individual contributions of the myofibrillar and the connective tissue components. The results are consistent with the suggestion that the initial yield force values represent mainly the myofibrillar strength and that the difference between the peak force and the initial yield force represents the contribution of the connective tissue.     

Tenderization of Chicken Muscle: The Stability of Alkali-Insoluble Connective Tissue During Post-Mortem Aging

SUMMARY— The relation between tenderness of breast and thigh muscles from chicken broilers and stability of connective tissue therein was measured during post-mortem aging. Tenderness was determined with a Warner-Bratzler shear-force apparatus and with a trained taste panel. Maximum shear-resistance values occurred in breast muscles 3 to 4 hr post-mortem; minimum values were reached 12 hr post-mortem and did not change significantly during aging for 8 days. Maximum shear-resistance values occurred in thigh muscles 3 hr post-mortem; in these muscles tenderization continued during 8 days of aging.
In contrast, alkali-insoluble connective tissue determined in either raw or cooked muscle (as measured by alkali-insoluble hydroxyproline) did not change significantly as a function of post-mortem aging time (1 hr vs 24 hr for breast meat, 1 day vs 8 days for thigh meat). Cooking solubilized considerable amounts of the connective tissue. Post-mortem tenderization of chicken meat is not related to changes in connective tissue but must be ascribed to some other fraction (or fractions) of muscle tissue.     

DIMENSIONAL CHANGES IN MEAT DURING COOKING

Continuous measurements of changes in meat fiber length with increasing temperature during cooking showed three zones where rates of length change are significantly different. The first (> 40°C) is attributed to myofibrillar change. The second (> 55 °C) is thought to be related to connective tissue shrinkage and shows differences with myofibrillar contraction state attributable to changes in spatial orientation of collagen fibers. The third zone (> 70 °C) is believed to be due to the interaction between myofibrillar and connective tissue contraction. Measurements of changes in cooking loss, length and cross-sectional area of samples of contracted and stretched muscle showed that cooking losses and the decrease in the cross-sectional area were greater in contracted samples, whilst length changes were greater in stretched samples. This has been attributed to differences in spatial orientation of connective tissue.     

Changes of meat quality characteristics and intramuscular connective tissue of beef semitendinosus muscle during postmortem aging for Chinese Yellow bulls

This study was designed to explore the changes of meat quality characteristics and intramuscular connective tissue of beef semitendinosus muscle during postmortem aging for Chinese Yellow bulls. Semitendinosus muscles were obtained at day 4 postmortem and then further aged for different periods. Chemical determinations, histological and mechanical measurements were performed for the raw and cooked steaks on days 4, 11, 14, 21, and 28 postmortem, respectively. The results showed that postmortem aging resulted in an increase in moisture content and collagen solubility, a decrease in filtering residues, primary perimysial thickness, fibre diameter, Warner‐Bratzler shear force, and transition temperature of the endomysium. The synergic effects of the myofibril and the intramuscular connective tissue determined the tenderness of aged beef.     

EFFECTS OF DRY AND MOIST HEAT ON SELECTED HISTOLOGICAL CHARACTERISTICS OF BEEF SEMIMEMBRANOSUS MUSCLE

ABSTRACT— Samples of raw and heat-treated beef semimembranosus muscle were examined histologically to determine how deep-fat frying, oven roasting, oven braising and pressure braising to 70°C affected histological characteristics of the muscle. A panel of three persons used an ocular micrometer to measure muscle fiber width, observed color and type of connective tissue and distribution of fat and estimated quantity of connective tissue of 475 histological sections. Differences among heat treatments in muscle fiber width and relative proportion of straight and wavy connective tissue were not significant. However, there was a significantly (P<0.05) larger quantity of granular tissue in deep-fat fried, pressure braised, and oven braised samples than in oven roasted samples. Intact fat cell walls were observed in both raw and heated samples.     

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.     

Intramuscular connective tissue and its role in meat quality

The amount, spatial distribution and composition of the connective tissue within muscle vary with muscle position in the carcase and with animal age. This has long been recognised to influence the tenderness of cooked meat. This paper builds upon some historical perspectives with a review of some recent clarifications of the biological function of intramuscular connective tissue (IMCT) and of its contribution to meat texture, which is clearly multifactorial. The perimysial component of IMCT varies most in amount between muscles and is also the IMCT structure most involved in defining the mechanical integrity of cooked meat. The distribution of perimysium defines muscle fascicle size (muscle "grain" size), which is also still regarded as an indicator of tenderness. Postmortem conditioning of meat has consistently been shown to reduce the strength of intramuscular connective tissue in the raw state, but with equal consistency, this has been shown not to affect the toughness of cooked meat. Cooking increases IMCT strength in the range 20-50 °C and decreases its contribution at higher temperatures and longer cooking times. Crosslinking of collagen in older animals is generally considered to result in tougher meat, although definitive links between mature crosslink content and cooked meat toughness have been difficult to prove. In the last quarter-century, IMCT has been increasingly viewed as a "background" contributor to meat texture, which is difficult to change. However, the large variation in perimysial content of muscles in one animal represents an incredible range of expression. This appears to be firmly fixed to the functional properties of different muscles. In particular, it is hypothesised that definition of muscle fascicle size and shape by the bounding perimysium is related to the need for sub-sections of the whole muscle to slip past each other in the normal contractile function of the tissue. Despite this, the amounts and composition of IMCT can be manipulated by animal nutrition and exercise, and factors affecting the turnover of IMCT may especially be a future target for manipulation of meat texture.     

Muscle Firmness and Structure of Raw and Cooked Arrow Squid Mantle as Affected by Freshness

Changes in firmness and structure of arrow squid (Loligo bleekert) mantle muscle during refrigeration (5°C) were studied. Shear force of raw mantle decreased sharply between 3 and 9 h refrigeration after killing. Light microscopic observations showed many pores between muscle cells in the softened raw samples. Transmission electron microscopic observations suggested that the spaces appeared as a result of detachment of muscle cells from connective tissues. After cooking the stored raw muscle, the shear force and muscle structure were almost the same for samples with different storage times. Freshness had an influence on raw squid muscle firmness and structure but not on cooked muscle.     

牛半腱肌肉结缔组织胶原蛋白热力特性热诱导变化DSC分析

探讨牛半腱肌肉结缔组织胶原蛋白热力特性的热诱导变化。牛半腱肌肉分别采用水浴和微波加热到内部终点温度分别为40、50、60、70、80℃ 和 90℃,研究结缔组织滤渣和热力特性在热处理过程中的变化。结果表明：结缔组织滤渣含量随着热处理温度的升高而增加,当加热温度分别为60、70℃ 和 80℃时,结缔组织滤渣含量在两种热处理方式间存在显著差异(P＜0.05)。在两种热处理方式中,40℃至60℃的内部终点温度是影响结缔组织胶原蛋白热收缩温度的关键加热温度。热诱导的结缔组织胶原蛋白热力特性的变化是水浴和微波加热牛肉胶原蛋白热收缩温度存在差异的主要原因。     

The influence of the collagen fibre network of muscle on the compliance and tensile strength of muscle samples subjected to loads at right angles to the muscle fibre axis

The pattern of subdivision of a muscle into fibre bundles by the perimysium was examined as a possible source of within sample variability of meat toughness attributable to the connective tissue component. It was shown that the pattern of subdivision into fibre bundles relates to the tendom surfaces and influences the compliance and toughness of a meat sample. In addition it was shown that greater plasticity of raw meat samples results in greater compliance under load. The procedure of defining sample orientation relative to the geometry of the component parts enables some of the within sample variability to be explained and controlled.     

SHEAR FORCE ANALYSIS AS AN INDICATOR OF CHANGES IN MECHANICAL STRENGTH OF ISOLATED BEEF INTRAMUSCULAR CONNECTIVE TISSUE DURING AGING

Intramuscular connective tissue (IMCT) was isolated from bovine semitendinosus (ST) muscles aged 3, 5, 7, 10, 14, 21, 28, and 35 days postmortem. Shear force values were collected from raw ST muscle and IMCT preparations to determine changes in mechanical strength (resistance to shearing) of the connective tissue fibers during postmortem aging. Statistical analysis indicated significant differences in mean shear force values of isolated IMCT preparations between aging periods (P < 0.001) but no consistent pattern of change in shear force values was detected. No significant change in shear force values of raw ST muscle during postmortem aging (P > 0.05) was observed. Other investigators have incorporated the same procedure and reported decreasing shear force values with increased aging times for IMCT preparations and raw ST samples. Our results were not in agreement with these findings.     

肌肉组织学特性与肉品质的关系

畜禽的肉品质受多种因素的影响,其中与肌肉组织学特性关系最为密切。骨骼肌是主要的可食性肉,它由肌纤维、结缔组织和肌内脂肪组成。本文综述了肌纤维类型、肌纤维直径、肌纤维密度、肌纤维面积比例、肌节长度、结缔组织特性、肌内脂肪含量与分布等肌肉组织学特性与畜禽肉品质的关系。