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.     

A theoretical approach of the relationships between collagen content, collagen cross-links and meat tenderness

This work concerns the relationship between meat tenderness and the rubber-like properties, i.e. pressure and elastic modulus, that endomysium and perimysium connective tissues develop when meat has been heated to a temperature above which collagen contracts. For rest length meats with similar intramuscular connective tissue morphology, and which are at the same ageing state and pH, the elastic modulus of the collagenous fraction of connective tissues is approximately proportional to the total number of collagen cross-links present per volume of meat. Calculations from various published experiments concerned with the effect on tenderness of muscle type, animal age, type, and sex from different species show that this modulus follows most of the variations of meat toughness. Moreover, the proportionality between the increase in this elastic modulus and the increase in meat toughness approaches unity in situations where toughness mainly depends on connective tissues. This work demonstrates the decisive role of rubber-like properties of connective tissues in meat tenderness variations.     

Effects of fibre type and kefir, wine lemon, and pineapple marinades on texture and sensory properties of wild boar and deer longissimus muscle

Fibre type percentage and changes in textural parameters, sensory properties as well as mean fibre cross sectional area (CSA), fibre shape, endomysium and perimysium thickness of wild boar and deer longissimus (L) muscle subjected to ageing with kefir, dry red wine, lemon and pineapple juice marinades for 4days were studied. Among the non-marinated and non-aged samples of muscles it was found that wild boar meat with its higher percentage of red fibres, higher CSA, thicker connective tissue as compared with deer meat, was harder, more springy and stringy. Muscles ageing, regardless of methods, resulted in a decrease in both the CSA and thickness of the connective tissue, and improve in fibre shape. As a consequence ageing caused a reduction in hardness, cohesiveness, springiness, and stringiness as well as in augmentation of tenderness, juiciness and general attractiveness of the muscles studied. As demonstrated by obtained data, regardless of ageing methods, deer L muscle contained more white fibres compared to wild boar muscle, were more susceptible to tenderization. The highest structural and textural changes, but the worst general attractiveness was found in muscles marinated with pineapple juice addition. Insignificantly lower changes in both quality traits were found in muscles aged with kefir marinade which at the same time were characterized by the high tenderness, the highest juiciness and general attractiveness.     

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.     

Factors associated with tenderness in young beef

One hundred and twenty-two crossbred steers of varying percentages of Bos Indicus and Bos Taurus breeding were slaughtered to determine the relationship of carcass and meat characteristics to tenderness. Carcasses were graded and longissimus dorsi muscle samples were evaluated for fibre type characteristics, sensory and shear force determination, sarcomere length, intramuscular fat content, collagen content and solubility and fragmentation index. Sarcomere length and collagen content and solubility were not significantly related to shear force values or sensory tenderness ratings. The fragmentation index was highly correlated to sensory tenderness ratings (r = −0·60) and shear force values (r = 0·53) indicating that variation in tenderness is associated with myofibrillar protein degradation. A four variable regression equation that included fragmentation index, lean colour, marbling and per cent red fibres accounted for 56% of the variation in sensory tenderness. Fragmentation index directly accounted for 30% of the variation in sensory tenderness in the four variable equation.     

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.     

Effects of fibre type and kefir,wine lemon,and pineapple marinades on texture and sensory properties of wild boar and deer longissimus muscle

Fibre type percentage and changes in textural parameters, sensory properties as well as mean fibre cross sectional area (CSA), fibre shape, endomysium and perimysium thickness of wild boar and deer longissimus (L) muscle subjected to ageing with kefir, dry red wine, lemon and pineapple juice marinades for 4 days were studied. Among the non-marinated and non-aged samples of muscles it was found that wild boar meat with its higher percentage of red fibres, higher CSA, thicker connective tissue as compared with deer meat, was harder, more springy and stringy.Muscles ageing, regardless of methods, resulted in a decrease in both the CSA and thickness of the connective tissue, and improve in fibre shape. As a consequence ageing caused a reduction in hardness, cohesiveness, springiness, and stringiness as well as in augmentation of tenderness, juiciness and general attractiveness of the muscles studied.As demonstrated by obtained data, regardless of ageing methods, deer L muscle contained more white fibres compared to wild boar muscle, were more susceptible to tenderization. The highest structural and textural changes, but the worst general attractiveness was found in muscles marinated with pineapple juice addition. Insignificantly lower changes in both quality traits were found in muscles aged with kefir marinade which at the same time were characterized by the high tenderness, the highest juiciness and general attractiveness.     

Contribution of postmortem muscle biochemistry to the delivery of consistent meat quality with particular focus on the calpain system

Tenderness has been repeatedly reported as the most important quality aspect of meat. However, a number of studies have shown that a significant portion of retail meat can be considered tough. As a consequence, a significant consumer segment is willing to pay a premium for guaranteed tender meat. However, apart from measuring the shear force, there is no reliable method to predict tenderness. Most of the branded meat programs therefore attempt to ensure eating quality by controlling some of the factors that affect tenderness. Meat tenderness is determined by the amount and solubility of connective tissue, sarcomere shortening during rigor development, and postmortem proteolysis of myofibrillar and myofibrillar-associated proteins. Given the effect of postmortem proteolysis on the muscle ultrastructure, titin and desmin are likely key substrates that determine meat tenderness. A large number of studies have shown that the calpain proteolytic system plays a central role in postmortem proteolysis and tenderization. In skeletal muscle, the calpain system consists of at least three proteases, μ-calpain, m-calpain and calpain 3, and an inhibitor of μ- and m-calpain, calpastatin. When activated by calcium, the calpains not only degrade subtrates, but also autolyze, leading to loss of activity. m-Calpain does not autolyze in postmortem muscle and is therefore not involved in postmortem tenderization. Results from a number of studies, including a study on calpain 3 knockout mice, have shown that calpain 3 is also not involved in postmortem proteolysis. However, a large number of studies, including a study on μ-calpain knockout mice, have shown that μ-calpain is largely, if not solely, responsible for postmortem tenderization. Research efforts in this area should, therefore, focus on elucidation of regulation of μ-calpain activity in postmortem muscle. Discovering the mechanisms of μ-calpain activity regulation and methods to promote μ-calpain activity should have a dramatic effect on the ability of researchers to develop reliable methods to predict meat tenderness and on the meat industry to produce a consistently tender product.     

Degradation in muscle fibre-connective tissue junctions in the spotted trevalla (seriolella punctata) examined by scanning electron microscopy

The junctions between the muscle fibres and the connective tissues of the myocommata in the spotted trevalla (Seriolella punctata Forster) were investigated by scanning electron microscopy. In prerigor muscle, the fine collagen fibrils which arise from the myocommata to form the muscle cell envelope were evident. After the fish were stored several days in ice, progressive deterioration was observed in these fibrils. The structure and the degradation was similar in nature to that reported previously in blue grenadier.     

Tenderization of Heated Sliced Beef by Succinylated Glycerol Monostearate, a Novel Meat Tenderizer

ABSTRACT Succinylated glycerol monostearate (SGMS) was most effective in reducing shear‐force value when used as a surfactant to tenderize meat using sheep casings as a model of intramuscular connective tissue. Roasted beef slices that had been treated with 2% granular SGMS showed a marked decrease in toughness due to the penetration of SGMS along the perimysium during heating. Collagen fibrils in the perimysium were transformed into a sheet‐like structure that seemed very likely to be a complex of SGMS and thermally denatured collagen. These structural changes could account for the tenderness of the roasted beef slices.     

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.     

Proportion of Collagen Types I and III in Four Bovine Muscles Differing in Tenderness

Intramuscular collagen containing both endomysial and perimysial tissue was extracted from four bovine muscles, analyzed for collagen types I and III, and related to total muscle collagen and meat tenderness. Isolated collagen was digested with cyanogen bromide and the proportion of collagen types I and III determined from densitometric scans of peptides resolved by SDS-PAGE. Total collagen was different (P<0.05) for each muscle. However, only the longissimus had more (P<0.05) type III collagen than did the biceps femoris, semimembranosus, and semitendinosus muscles. Percentage type III was correlated with sensory panel connective tissue amount (0.48) and overall tenderness (0.48) scores for the longissimus and biceps femoris muscles.     

肌内胶原蛋白与肉品质关系研究进展

肌内胶原蛋白是一种重要的肌肉组织成分,是构成肌内结缔组织的主要组成部分,在维持肌肉结构、柔韧性、强度和质地等方面起着重要作用。胶原蛋白影响肉的嫩度被称作是背景硬度(或基础硬度),胶原蛋白对肉嫩度的影响主要取决于其含量、热溶性、交联度及其热稳定性程度等。本文概述肌内胶原蛋白的特性以及与肉嫩度之间的关系,并对今后研究进行展望。     

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.     

Tensile strength and the tenderness of beef sternomandibularis muscle

In their relationship to shortening, the tensile strength of cooked meat along the fibres and the shearing force measured across them are strikingly similar. Both increase to maximum values at 40% shortening before falling by a half with an approach to 60% shortening. A high correlation (r = 0·81) exists between the two sets of values, whether toughness is increased by cold shortening or reduced by ageing. The mechanical strength of meat along its fibres is therefore a simple measure of tenderness and a useful basis for relating muscle structure to stength.     

The effect of pre-rigor stretch and contraction on the post-rigor geometry of meat samples in relation to meat toughness

The geometry of the muscle fibre and perimysial collagen components of meat subjected to pre-rigor stretch and contraction were examined. The changes in the configurations of these two components accompanying length changes in the muscle were used to explain the reported relationship between raw meat toughness and contraction state. The theory put forward proposes that in raw meat samples the muscle fibre component plays virtually no role in modifying the toughness of the meat sample with contraction state. This theory of the collagen component playing the major role is the same as that reported elsewhere. It is capable of explaining a reverse relationship between meat toughness and contraction state such as is found in cooked meat simply by invoking a firmer consistency for the muscle fibres which then act as fill between the collagen network fibres and hold them at an angle relative to the line of applied force.     

肌肉结缔组织与肉嫩度关系研究(英文)

Intramuscular connective tissue(IMCT) has made significant effects on meat tenderness;those effects were executed by the characteristics changes of endomysial and perimysial collagen.The review presents the progress of structural and composition properties of connective tissue as well as contents,solubility and crosslinking of collagen,moreover,the effects of characteristics changes of connective tissue and collagen on meat tenderness and textural properties during postmortem ageing were analyzed and the role of connective tissue in meat tenderization were discussed.     

肌内结缔组织与肉嫩度关系研究

动物肌内结缔组织对肉的嫩度起到重要的影响作用,这些影响主要是通过肌内膜和肌束膜内胶原蛋白的变化而影响肉的嫩度。本文综述了肌内结缔组织结构及其组成特点,胶原蛋白的含量、溶解性、交联度,另外,分析了胶原蛋白在成熟过程中的变化对肉嫩度的影响,阐述了结缔组织在肉嫩化中的作用。     

Composition of muscle fibre types and connective tissue in bovine M. semitendinosus and its relation to tenderness

The distribution of muscle fibre types and connective tissue in bovine M. semitendinosus is described. A parallel increase in the volume fraction of type I muscle fibres (from 10% to 30%) and a decrease in the IIB volume fraction (from 58% to 34%) was recorded from superficial to deep layers. A positive correlation was observed between the frequency and the cross-sectional area of both type I and IIB fibres. The elastic fibres formed irregularly shaped bundles that made up about 50% of the volume of the perimysium. Thin elastic fibres extended into the endomysium. The relative proportion of elastic fibres in the perimysial connective tissue increased towards the deeper layers of the muscle. A taste panel evaluation of the sensory properties was performed and the data were correlated to the histological observations. A gradual decrease in scores of four tenderness-related traits was recorded from the superficial to the deep layer of the muscle. The superficial layer was rated as most tender, whereas the consecutive layers were rated less tender. The possible relationship between the composition of muscle and the meat quality is discussed.     

Cold shortening and cooking changes in beef

Quantitative relationships have been established between pre-rigor shortening in beef sternomandibularis muscle and cooking shrinkage and weight loss. Shortening induced by cold increases cooking weight loss and shrinkage across the meat grain, but reduces shrinkage along the fibre direction. The mechanism of fluid discharge from meat on cooking is determined by the degree of pre-rigor shortening. In unshortened meat, cooking shrinkage along the fibre precedes discharge and transverse swelling occurs to accommodate entrapped fluids. During the cooking of highly shortened meat, fluid discharge occurs mainly across the fibres, the sarcolemmas of which presumably have been split during shortening. Consequently early swelling on cooking does nccur.