The strength and stiffness of perimysial connective tissue isolated from cooked beef muscle

Thick transverse slices of bovine M. semitendinosus were cooked for 1 h at 50°–90° and then cooled. Perimysial connective tissue was dissected from the cooked meat and subjected to mechanical testing in a small-scale device. The initial ‘toe’ region of the J-shaped load-extension curve was progressively lost with increasing temperature, the curve becoming more nearly linear after cooking at 90°C. These effects are explained on the basis of the progressive straightening out of the crimps from the collagen fibres, the crimps becoming finally lost at approximately 70°C. The final stiffness of the perimysium at greater extensions was unchanged at higher temperatures. Breaking strength increased from raw to cooked at 50°C, thereafter decreasing at cooking temperatures up to 90°C. it is proposed that this technique of testing isolated perimysium gives a valuable means of directly measuring the effects of cooking, or other treatments, on the intrinsic properties of perimysial collagenous material. Quantitative knowledge of these will help to determine its contribution to the overall mechanical properties, and hence eating quality, of cooked meat.     

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.     

The effects of conditioning on meat collagen: Part 2-Direct biochemical evidence for proteolytic damage in insoluble perimysial collagen after conditioning

The effect of proteolytic attack on unwashed and 6 M urea washed bovine perimysial collagen was examined using model systems. Pepsin and cathepsin solubilized collagen continuously over 24h (r = 0·95 andr = 0·88 for time course of pepsin and cathepsin solubilized collagen). Insoluble perimysium treated with pepsin over 24 h resulted in little damage to the insoluble collagenous residue remaining, as evidenced by one-dimensional SDS-polyacrylamide gel electrophoresis. Insoluble perimysium treated with cathepsin resulted in changes to the major peptide bands which were evident after 24 h treatment, visible as broadening and 'fuzziness' of bands, decreased staining intensity, loss of high molecular weight material and a significant reduction in quantity of all peptides when compared with untreated perimysium. The effects of proteolytic action on bovine perimysial collagen in vitro and in conditioned meat were investigated by means of two-dimensional polyacrylamide gel electrophoresis, which provided a more sensitive technique for elucidating changes than the one-dimensional method. The peptide maps obtained from conditioned insoluble perimysium and from insoluble perimysium treated with cathepsin for 24 h were altered relative to the unconditioned insoluble perimysium, with the loss of some peptides and generation of others. The in vitro case was extreme, but was comparable with samples of perimysium from conditioned muscles. The results provide direct biochemical evidence for the presence of proteolytic damage in the insoluble perimysial collagen matrix of meat after conditioning.     

Image analysis study of the perimysial connective network,and its relationship with tenderness and composition of bovine meat

Image processing method was developed to predict beef tenderness, collagen and lipids contents. The study was carried out on the semimembranosus muscle (SM). Images of SM slices were acquired under visible and ultraviolet lighting. In this work statistical technique was implemented as a method to relate the distribution of intramuscular connective tissue (IMCT), characterized by image analysis, to sensory tenderness evaluated by a trained panel and collagen and total lipids contents assessed chemically. Using Multiple Linear Regression (MLR) combining visible and ultraviolet lighting, IMCT image parameters were found to be good predictors of beef tenderness (R² = 0.89), collagen and lipids contents (respectively R² = 0.82 and R² = 0.91).     

Connective tissue differences in the strength of cooked meat across the muscle fibre direction due to test specimen size

Systematic variations in the tensile strenght of cooked beef M. semitendinosus across the muscle fibre direction due to the cross-sectional size of specimens are demonstrated in specimens from (a) longitudinal and (b) transverse slices. The strength perpendicular to the fibre direction of longitudinal slices of thickness 0·25-5·75 mm varied by a factor of 2, thicker slices being stronger. This factor of 2 is in approximate agreement with the difference in strength of transverse versus longitudinal slices across the fibre direction. These variations of strength due to specimen geometry are explained on the basis of the increasing likelihood of including a ribbon of the perimysial connective tissue network which is continuous along the whole length of the test piece in larger samples. The breaking strength of small cross-sectional area specimens is likely to be dominated by the strength of the endomysial-perimysial junction. Larger cross-sectioned specimens, by including continuous strands of the perimysial network, have higher strengths resulting from the necessity to break these strands. These findings highlight the need to specify specimen dimensions in tensile test results. They also show that by manipulating specimen geometry, the relative magnitude of the two mechanisms of connective tissue fracture (endomysial-perimysial separation and perimysial strand fracture) may be assessed.     

Texture of cooked potatoes: The effect of ions and ph on the compressive strength of cooked potatoes

It was shown from experiments on disks cooked in solutions of calcium chloride and calcium acetate, and in buffered solutions of calcium chloride at various pHs (sodium concentration constant) and from experiments where the ratios of disks to calcium chloride were varied, that the effect of calcium in increasing the compressive strength of the disks was small compared to the effect of reduced pH. The interaction of sodium and calcium was investigated at pH 6 (≈? the pH of cooked potato tissue). The effect of sodium in reducing compressive strength of the disks outweighed the effect of calcium in increasing compressive strength. Sodium and potassium chloride had a similar effect on loss of compressive strength on cooking. Increased compressive strength due to pH or the presence of calcium was overcome by extending the length of cooking. It is suggested that transelimination, ion exchange and hydrogen bond breakage may be more important factors than the chelation of calcium by naturally occurring phytin, in the breakdown of pectic substances and loss of intercellular adhesion during normal cooking of toes.     

The effect of phytic acid on oxidative stability of raw and cooked meat

The effects of phytic acid addition (0.1, 1 and 5 mM) to pork and beef homogenates on TBARS and metmyoglobin levels in raw meat, and TBARS and heme iron contents in cooked meat during 3 days of storage at 4 °C were investigated. Also, the role of inositol as a potential synergist of IP₆ (phytic acid) was examined. IP₆ effectively decreased the TBARS accumulation in raw and cooked meat homogenates. The metmyoglobin formation was inhibited in raw beef by phytic acid in a dose-dependent manner. The effect of IP₆ was more pronounced in cooked meat than in raw and in cooked beef homogenates more than pork. Inositol did not enhance antioxidant action of phytic acid in minced meat.     

超声波处理对结缔组织胶原蛋白和肉嫩度的影响

近年来,有许多研究报道了超声波在肉嫩化中的应用.超声波处理对肉质构的影响主要是由于超声波直接或间接的"空化效应".本文综述了超声波技术在肉类工业中的应用,主要阐述了不同频率和强度超声处理对肉"背景硬度"-肌内结缔组织及胶原蛋白特性的影响;同时,预测了超声波技术在肉类工业中的应用.     

The effect of pH on the formation of maillard-derived aroma volatiles using a cooked meat system

The effect of pH on the formation of volatile compounds was investigated using minced beef in which the pH was adjusted within the range 4.0–5.6, by the addition of hydrochloric acid before cooking. The strong buffering capacity of the meat ensured that the pH did not vary during heating. Volatiles were analysed using headspace concentration and gas chromatography-mass spectrometry. The total quantity of volatile compounds increased as the pH decreased. A number of furanthiols and their oxidation products were preferentially formed at acid pH; some of these compounds had strong meaty aromas. The formation of other heterocyclic compounds such as thiazoles and pyrazines were favoured by higher pH.     

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.     

Structural weakening of intramuscular connective tissue during conditioning of beef

The structural changes in intramuscular connective tissues endomysium and perimysium during conditioning of beef were investigated using an improved technique of scanning electron microscopy. In beef conditioned for 28 days of 4°C, the endomysium resolved into individual collagen fibrils and the thick sheets of perimysium separated into collagen fibres of 4-8 μm in diameter. These results provide direct evidence for the structural weakening of endomysium and perimysium during conditioning. The structural changes in the intramuscular connective tissue were minimal until 10 days post mortem, but clearly observable after 14 days post mortem. Therefore, it is concluded that intramuscular connective tissue shows the effect on tenderisation of extended conditioning (2-4 weeks) of beef.     

The properties of connective tissue membrane and pig skin as raw materials for cooked sausage

Pig skin and epimysial membrane from young bulls were comminuted in a colloid grinder and mixed with water and additives. The resultant mixture was heated in a water bath to give an internal temperature of 72°C, and centrifuged while still hot. Such variations in the amount of water added, the salt content, the phosphate content and the pH value as are possible in cooked sausage heated to over 65°C during processing did not cause marked changes in the amount of water bound by the connective tissues, the amount of dissolved protein or the gel strength of the liquid released from the connective tissues. As the temperature rose the amount of bound water dropped, but the amount of dissolved protein and the gel strength increased. The liquid released from the connective tissue membranes formed a gel at 32°C and re-melted at 49°C. For pig skin, the corresponding temperatures were 23°C and 47°C. On the basis of this study it appears that connective tissue may be important for the water-binding capacity and firmness of cold sausage. The connective tissue membranes obtained from young bulls and pig skin are of roughly equal value in this respect, although the gel formed from connective tissue membrane is tougher.     

The relation of the biological value of meat proteins to their content of connective tissue

The influence of connective tissue on the biological value of meat products, manufactured from hashed meat, was studied in experiments on growing rats. It was shown that collagen level increase from 6.1 to 14.5% of the total amount of meat proteins improved the growth-mass characteristics of the animals. The actual biological value and the absolute protein utilization had a tendency to lowering, although the difference was not statistically significant. At the same time the effectiveness of tissue protein biosynthesis was not lowered. A conclusion has been made that the results of animal experiments correlate with the clinical data on the positive effect of the increase up to 15% (by protein) of collagen content on the anabolic action of hashed meat protein in humans. A further increase of the connective tissue amount leads to its diminished biological value.     

The effect of the change from a herbage- to a concentrate-based diet on the oxidative stability of raw and cooked lamb meat

Over 89 days, 10 lambs (S) were fed concentrates and hay in stall, while 9 lambs (P) grazed at pasture. Two groups of 9 animals grazed at pasture until switching to a concentrate-based diet for 14 or 37 days before slaughter (P-S14 and P-S37). The fat content of longissimus dorsi muscle (LM) increased with increasing duration of concentrate feeding (P = 0.05). As a consequence, the concentration of polyunsaturated fatty acids (PUFA) and of the highly peroxidisable (HP) PUFA in the polar lipids was similar between treatments. Lipid oxidation in fresh LM over 8 days of storage was affected by the diet (P < 0.0005) with the P-S37 and P treatments producing, respectively, the highest and the lowest TBARS values. The P treatment reduced TBARS in cooked minced LM over 2 days of storage and no difference was found between the P-S14, P-S37 and S treatments. Colour stability of fresh LM was not noticeably affected by the dietary treatment.     

Contribution of myofibrillar and connective tissue components to the Warner-Bratzler shear force of cooked beef

Myofibrillar (MF-SF) and connective tissue (CT-SF) peak shear forces were interpolated from Warner-Bratzler shear force (SF) deformation curves of cooked bovine M. gluteus medius (GM) and M. semitendinosus (ST) from 112 crossbred steers in a 2×2×2 factorial experiment examining the interactions between slaughter age, growth promotants and breed cross (British versus Continental). Mixed model analyses, Pearson correlations and stepwise multiple regression identified relationships between shear forces, meat quality measurements and production treatments. Connective tissue contribution to SF increased with slaughter age and implantation in the ST and with slaughter age only in the GM. Myofibrillar contribution to SF increased with slaughter age for the ST and with Continental genetics for the GM. Variation in ST SF and MF-SF was best described by muscle weight, which increased with animal age, while GM SF and MF-SF variation was best described by cooking loss, indicating that ST and GM SF were most affected by connective and myofibrillar proteins, respectively.     

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.     

The tenderness of cooked and raw meat from young and old beef animals

The shortening-toughness relationships for sternomandibularis muscles of young ox and large old bull have been compared. In both, toughness, measured by tenderometer, increases to a maximum at a shortening of 40%, and declines steeply from there at higher shortenings. This characteristic peaked relationship is obtained for ox and bull cooked both at 60 and 80 °C. However, toughness values for meat cooked to 60 °C are only about half those for meat cooked to 80 °C. In contrast to these similarities in the relationships for young and old animals, the rate of toughness increase with shortening in ox is considerably less than in bull. Thus toughness of ox at a given shortening and cooking temperature is considerably lower than that for bull, especially at high shortenings. A further distinction is made between the animals in that raw ox muscle does not give a peaked shortening-toughness relationship, whereas raw old bull does. The results have shown that for longissimus and sternomandibularis muscles a trained taste panel is only sensitive to variations in toughness in the lower half of the range of shear force values determined by tenderometer. In the light of this, live animal characteristics and muscle shortening are both important in determining toughness measured by taste panel.     

Technological properties of date paste obtained from date by-products and its effect on the quality of a cooked meat product

Fresh date processing (picking, storage or conditioning) may lead to date losses. Such by-products from fresh dates (Medjoul variety) can be processed to prepare date paste. Chemical composition, physicochemical and technological properties of this date paste were determined regarding its potential application as an ingredient in the elaboration of meat products. The date paste had a high content of sugars (53.00 g/100 g) especially reducing sugars (fructose and glucose), total and insoluble dietary fiber (7.00 g/100 g and 4.04 g/100 g, respectively) and natural antioxidants (polyphenol content; 225 mg GAE/100 g). Its emulsion capacity was 57.00 mL/100 mL and it showed also a high emulsion stability (98.59 mL/100 mL). The addition of up to 15% date paste in the formulation of bologna-type products leads to the enhancement of the nutritional (lower fat content and higher fiber content than control) and technological quality (redder-colored and less hard, chewy and cohesive product than the control) together with a satisfactory sensory quality.