Gelation of chicken breast and thigh muscle homogenates: effect of pH and time of aging

Gelation properties of chicken breast and thigh muscle homogenates were studied at various pH values. Breast muscle homogenates showed a greater protein extractability at pH 5.8-6.6 and gel strength at pH 6.3-6.6 than thigh muscle homogenates. At pH 5.8-6.0 breast muscle homogenate gels were weaker than thigh muscle homogenate. The pH for optimum gelation, indicated by the highest stress at failure was 6.3 for breast and 6.0 for thigh muscle homogenates. The pH dependence of chicken breast and thigh muscle homogenate gel strengths, influenced by the muscle fibre type, probably was due to altered protein-protein and other meat component interactions and changes in protein extractability.     

Influence of breed and muscle metabolic type on muscle glycolytic potential and meat pH in pigs

Glycolytic potential and activities of myofibrillar ATPase, lactate dehydrogenase, citrate synthase, glycogen synthetases and glycogen phosphorylases were measured in five muscles from five Large White, eight Pietrain, seven Belgian Landrace and eight Penshire pigs (Penshire is a composite line including 50% Hampshire, 35% Duroc and 15% Large White blood). Additionally, ultimate pH was measured on the loin and four ham muscles. Muscles could be classified as follows on the basis of enzyme activities: Longissimus dorsi and Semimembranosus as 'fast white', Rectus abdominis as 'intermediate'. Trapezius and Masseter as 'slow red'. Small breed differences were observed in enzyme activities except for citrate synthase activity and degree of activation of glycogen phosphorylase in the 'fast white' muscles. Large Whites, Pietrains and Belgian Landraces did not differ in glycolytic potential whatever the muscle involved. Compared with these three breeds, Penshires had much higher glycolytic potential values in the 'fast white' muscles (+51 to 75%) and in the 'intermediate' muscle (+29 to 56%). However, in the 'slow red' muscles, there was almost no difference in this trait between the four breeds. The Penshire pigs showed lower ultimate pH than the pigs from the other breeds in three of the four ham muscles studied. It is concluded that muscle metabolic type must be considered when assessing breed variation in glycolytic potential, and that the high muscle glycolytic potential characterizing the Hampshire could be inherited as a dominant trait in Hampshire crosses.     

Apparent shear viscosity of native egg white

Temperature and shear dependency of the apparent viscosity of the thick and thin portions of egg white from fresh hen eggs, in their native state was investigated. The viscosity of the egg white was determined in the temperature range of 5–30°C and the shear rate range 34–600 sec^-1. The viscosity of both the thick and thin portions of the egg white decreased with increase in temperature. The thin portion showed no decrease in viscosity with shearing time at constant shear rates while the viscosity of the thick portion decreased within the first 6 min of shearing and then remained constant. The rate of decrease in viscosity with shearing time was more at higher temperatures. At 20°C and a shear rate of 34.2 sec^-1, the equilibrium-apparent viscosity of the thick portion was 160 cp, approximately forty times greater than that of the thin portion (4cp). This difference in viscometric properties may be due to the presence, in the thick portion, of high molecular weight complexes which are disrupted under shearing.     

Chicken muscle homogenate gelation properties: effect of pH and muscle fiber type

Gelation properties of chicken breast and thigh muscle homogenates at a protein concentration of 4.5% under different pH conditions (5.80–6.60) and those of myofibrillar proteins at a protein concentration of 2% were compared to determine the influence of muscle fibre types on gelation. The optimal gelling pH for breast muscle homogenates (pH 6.30) was slightly higher than that for thigh muscle homogenates (pH 5.80–6.30), a similar trend was found for the isolated chicken myofibrillar proteins (pH 6.00 for breast and 5.50 for leg). Similarly, the pH values at which breast muscle homogenate gels were weaker (pH<6.20) or stronger (pH6.20) than thigh muscle homogenate gels were higher when compared with chicken breast and leg myofibrillar protein gels (pH<5.80 and pH>5.90, respectively).     

Measurement of autolysis in beef muscle homogenates

Homogenates of beef longissimus dorsi muscle have been used to study the effect of pH, temperature and Ca(2+) ions on post-mortem autolysis. Measurements of myofibrillar proteins were made after SDS-polyacrylamide gel electrophoresis and it was found that the intensity of the troponin T band could be used as an indicator of autolysis. At pH values below 6·0, the addition of EDTA increased the rate of loss of troponin T: above pH 6·0, the rate of loss of troponin T was accelerated by Ca(2+) ions. It was concluded that there were at least two proteolytic enzyme systems involved-cathepsin B at low pH and a calcium-activated factor at high pH.     

Effects of pH on the functional properties of chicken muscle proteins- modified waxy cornstarch blends

ABSTRACT:  Chicken breast muscle powder (CBMP) and modified waxy cornstarch (MWCS) blends were prepared at different pH conditions (pH 4, 5, 6, 7, 8, and 9). The blends were characterized by light microscopy, frequency sweep, flow analysis, and freeze-thaw stability analysis. Light microscopy showed that the blend structure was coarse at pH conditions close to the isoelectric point of protein and became finer with increasing pH. Frequency sweep demonstrated that the blend was more liquid-like with relatively lower storage ( G ') and loss ( G ") moduli as the pH was increased from pH 4 to pH 9. Flow analysis revealed that thixotropy behavior was evident in samples treated at pHs 4 and 5, whereas antithixotropy was shown by those adjusted to pHs 6, 7, 8, and 9. The CBMP–MWCS blends were found to show better freeze-thaw stability at pH 8 that could be attributed to the formation of a highly interactive network structure of CBMP and MWCS.     

Influence of breeding systems on pH and histochemical properties of muscle fibres in porcine M. semimembranosus

The purpose of this study was to investigate pH values, fibre type frequency and histological features of Semimembranosus muscle of 15 pigs subjected to three breeding systems. The A group was raised in a large paddock; the B group animals were raised in a collective pen until they reached a live weight of 120 kg and then in the same paddock as the A group; the C group was raised in a collective pen. Breeding systems had no significant effect on pH values and fibre type frequency. Histopathological changes in muscle fibres and connective tissue were observed in 12 of the animals studied regardless of the group. However, analysis of the incidence of alterations showed a higher frequency of lesions in the B group, followed by the C group.

Except for one case of DFD meat, muscle alterations were not associated with an adverse pH. In addition, regenerating fibres, with strong reactivity for neonatal serum, were observed both in apparently healthy and in pathological muscle samples.     

Influence of early pH decline on calpain activity in porcine muscle

This study investigated the influence of post-mortem pH decline on calpain activity and myofibrillar degradation. From 80 pigs, 30 Longissimus dorsi (LD) muscles were selected on the basis of pH values at 3 h post-mortem and classified into groups of 10 as fast, intermediate and slow pH decline. The rate of pH decline early post-mortem differed between the three groups, but the ultimate pH values were similar at 24 h. Calpain activity and autolysis from 1 to 72 h post-mortem were determined using casein zymography and studied in relation to myofibrillar fragmentation.     

高压和热结合处理对鸡肉pH、嫩度和脂肪氧化的影响

对不同温度(20～70℃)下高压(0.1～800MPa)处理20min对鸡胸肉pH、嫩度和脂肪氧化的影响进行了研究。结果显示,压力和热或两者结合处理都能使肌肉的pH升高,但两者结合处理对pH的影响无叠加作用。单纯的热处理过程中,随着温度的升高,肌肉的嫩度持续下降,同样,室温下的压力处理时,肌肉的嫩度随压力的升高而降低。40℃时压力处理,肌肉嫩度的变化与室温下相似。然而,当在60℃和70℃温度下压力处理时,200MPa的压力导致肌肉的嫩度显著提高。其原因可能为在此条件下肌肉骨架蛋白质发生了降解。压力和热以及两者结合处理都能加速脂肪的氧化,尤其是在400MPa及其以上压力。压力和热处理导致脂肪氧化的原因,可能与肌肉结构的破坏及过渡金属离子(如铁离子)的释放有关。     

Influence of muscle type on physicochemical and sensory properties of foal meat

The effect of muscle type on physico-chemical properties and sensory characteristics of foal meat was investigated. Six muscles: longissimus dorsi (LD), semimembranosus (SM), semitendinosus (ST), biceps femoris (BF), triceps brachii (TB) and psoas major & minor (PM) from twelve foals slaughtered at 15 months from an extensive production system in freedom regimen were extracted for this study. Regarding chemical composition, intramuscular fat content showed significant differences among muscle where PM presented higher values (0.7%) than the other ones. The heme-iron content also presented significant differences ranging between 1.5 and 2.4 mg/100 g fresh meat. ST was the lightest, while TB and PM presented a more intense redness. The muscles that had a greater capacity to hold water were ST and BF, which presented lower drip loss (2 and 2.2%) and cooking loss (17.3 and 17.2%), respectively. Textural traits established the following scale in response to the tenderness: LD > PM > ST > TB > BF > SM. Finally, sensory analyses revealed that color and texture traits (hardness, juiciness and fibrousness) were significantly influenced by muscle type.     

Protein Concentration, pH and Ionic Strength Affect Apparent Viscosity of Actomyosin

Response surface methodology was used to compare effects of NaCl protein concentration, and pH on apparent viscosity (ζapp) of natural actomyosin from hake, pork and chicken muscle. Models for the three species had R² of 0.921, 0.915 and 0.814 (P<0.01) for chicken, pork and hake, respectively. Protein concentration and pH increased qapp, whereas higher ionic strength decreased it and had less influence. Interactions occurred between protein concentration and pH. Models did not reveal inter-species differences (P<0.05). However, analysis of variance of regression coefficients for each variable showed some differences due to pH.     

Antioxidant effect of fractions from chicken breast and beef loin homogenates in phospholipid liposome systems

The antioxidant effects of meat fractions from chicken breast and beef loin were compared. Five meat fractions – homogenate (H), precipitate (P), supernatant (S), high-molecular-weight (HMW) and low-molecular-weight (LMW) fractions – were prepared from chicken breast or beef loin. Each of the fractions were added to a phospholipid liposome model system containing catalysts (metmyoglobin, ferrous and ferric ion) or iron chelating agents to determine the effects of each fraction on the development of lipid oxidation during incubation at 37 °C for 120 min. All fractions from chicken breast showed stronger antioxidant effects against iron-catalyzed lipid oxidation than those from beef loin. Iron chelating capacity of water-soluble LMW and water-insoluble (P) fractions from both meats were responsible for their high antioxidant capacities. High concentration of myoglobin, which served as a source of various catalysts, was partially responsible for the high susceptibility of beef loin to lipid oxidation. Storage-stable ferric ion reducing capacity (FRC) was detected in all fractions from both meats, and was a rate-limiting factor for lipid oxidation in the presence of free ionic iron. Higher antioxidant capacity and lower myoglobin content in chicken breast were primarily responsible for its higher oxidative stability than beef loin. DTPA-unchelatable compounds, such as ferrylmyoglobin and/or hematin were the major catalysts for lipid oxidation in beef loin, but free ionic iron and storage-stable FRC also played important roles during prolonged storage.     

Bacterial penetration of chicken breast muscle

Pure cultures of motile, but not non-motile strains of bacteria penetrated blocks of chicken breast muscle, irrespective of ability to hydrolyse gelatin, casein or soluble meat proteins. Penetration occurred as a result of movement of bacteria between the endomysial sheath and associated muscle fibres. Rates of penetration recorded were temperature dependant, affected by tissue moisture content and favoured by proteolytic activity, but were independent of growth rate. In addition, mixtures of proteolytic and non-proteolytic cultures enhanced the penetration rate of the non-proteolytic strains. Other experiments using mixed inocula, indicated some strains of non-motile, non-invasive bacteria may be carried into muscle by motile, invasive strains.     

Effect of muscle type, salt and pH on cooked meat haemoprotein formation in lamb and beef

The rate of cooked meat haemoprotein formation, measured as the rate of loss of myoglobin solubility, in lamb was dependent on the muscles anatomical location and temperature. Lamb longissimus dorsi musle at 55 to 70°C formed cooked meat haemoprotein more rapidly than the muscles in the shoulder and leg. The formation in lamb was more rapid than in beef. The rate in high pH beef (7.25) l. dorsi was lower than found in beef l. dorsi of normal pH but in low pH lamb (5.38) l. dorsi the rate was, at most temperatures, also slower than found in this muscle from lamb of normal pH. In the presence of NaCl the rate of cooked meat haemoprotein formation was faster (almost doubled at 2g/100g meat) than found in the corresponding salt free lamb and beef samples. Other additives commonly added to meat products (mechanically recovered meat, oil, polyphosphates, soya, whey and caseinate) had little effect on the rate of cooked meat haemoprotein formation, at the levels normally used in meat products. It is concluded that for lamb products little if any myoglobin will remain soluble, and the products will look cooked before the recommended thermal treatment to inactivate Escherichia coli O157:H7 has been achieved. ?     

低粘度磷酸酯淀粉浆料与递质pH的依赖关系

在pH值为2．0～7．0范围内，制备不同的样品，以粘度、粘度稳定性、浆膜性能及浆液粘附性能为量化指标，研究了磷酸酯淀粉粘度与制备递质的pH依赖关系．结果表明，起始pH值对粘度的影响较显著，pH值范围不同，影响程度和方式也不同，当pH≤4．0时，粘度降低较快，主要发生淀粉链水解，浆膜性能及浆液粘附性较差；pH≥6．0，淀粉开始发生交联，粘度逐渐增加、稳定性降低；4．8≤pH≤5．4，淀粉水解适中，能获得粘度、浆膜性能及浆液粘附性较好的磷酸酯淀粉，尤以pH=5．2为优；在该pH值范围内，未观察到粘度稳定性与pH较明显的规律性变化关系．     

The post-mortem pH of cod and haddock muscle and its seasonal variation.

The post-mortem pH of cod muscle, which strongly influences its attributes as a food, is subject to seasonal variation. For most of the year the average of a batch lies above about 6.7, but for a short time in the summer it suddenly drops to low values, rising again just as suddenly. It is now thought that heavy feeding immediately after starvation causes this sharp fall. Fillets from fish frozen at such a time gape and have a tough texture after cooking. The low-pH period is fairly short, so cod are in fact suitable for freezing for all of the year outside certain summer months. The phenomenon has been observed in cod from a wide range of fishing grounds. Haddock show no such seasonal variation, but their post-mortem pH is lower on average than that of cod.     

Studies on chicken actomyosin. I. Effect of storage on muscle enzymic and physico-chemical properties

Experiments were conducted to study the effect of storing broiler chicken muscle at 25°C on certain properties of actomyosin of the pectoralis major. Storage for 3 h or more resulted in the Mg²⁺-activated ATPase of actomyosin becoming less sensitive to inhibition by increasing concentrations of KCl and in an increased rate of superprecipitation of the complex. The analytical ultra-centrifuge pattern of the actomyosin of stored muscle differed from that of fresh muscle. Some evidence was obtained for the observed changes being partly dependent upon the pH of the muscle used as the source of actomyosin.     

Effect of pH on Apparent Viscosity of Wholemeal Oat Flour Water Dispersions

Research was undertaken to determine the effects of pH (1.5–12), stabilization time (1–3 h), and shear rate (200–1200 s^?1) on the apparent viscosity of wholemeal oat flour—water dispersions (10% w/w). Six oat cultivars, with different content of dietary fibre, especially of (1–3) (1–4) β-D-glucans, were used in this study. The study demonstrated instability of apparent viscosity of wholemeal oat flour dispersions. An increase of viscosity was observed with the increase in stabilization time. The range of viscosity changes was related with the dispersion pH level—the greatest range of changes was noted for dispersion with pH 9.5. Wholemeal oat flour dispersions, irrespective of the pH level, displayed pseudoplastic flow behaviour. A moderate to high significant linear correlations (Pearson, p ≤ 0.05) existed between the apparent viscosity and the (1–3) (1–4) β-D-glucans, soluble dietary fibre and total dietary fibre content. Measurements of apparent viscosity of wholemeal oat flour water dispersions can be used for the estimation of particular dietary fibre fractions content, especially of (1–3) (1–4) β-D glucans. With the application of suitable measurement conditions, the content of (1→3) (1→4) β—D glucans can be explained by the apparent viscosity of the oat flour dispersion (R² = 0.97–0.98).     

Pressure-induced pH and length changes in muscle

The response to increase in pressure of pre- and post-rigor muscle strips supporting a load has been investigated by measuring length changes with application of pressure up to 150 MPa in a windowed pressure vessel. The response of the pre-rigor strips depended on temperature; at 30°C the strips contracted, then, after some minutes, lengthened, presumably because of a breakdown of myofibrillar integrity. At 0°C the cold-shortened muscle lengthened but if pressure was released the strips shortened again. Loaded post-rigor muscle strips lengthened with application of pressure. It is suggested that the conditions that prevail in pre-rigor muscle are not as favourable for disaggregation of the myofilaments as those in post-rigor muscle. Measuresurement of pH changes in pre-rigor pressure-treated muscle showed these were accelerated at 30°C, but completely inhibited by treatment at 0°C for 3 or 24h.