THERMAL GELATION OF DUCK BREAST AND LEG MUSCLE PROTEINS

Gels were made by heating duck breast and leg myofibrillar protein suspensions (20 mg/ml; pH 5.50, 5.75 and 6.00) at a constant rate of 1C/min from 18C to 70C. After heating the suspensions to 70C at pH 5.50, breast proteins formed gels which were not different (p > 0.05) in strength from leg proteins. At pH 5.75 and 6.00, however, breast proteins formed significantly stronger gels than leg proteins. Increasing the protein suspension pH from 5.50 to 5.75 had no significant effect on the strength of leg protein gels, whereas the strength of breast protein gels more than doubled. A further increase in pH from 5.75 to 6.00 resulted in a three-fold decrease in the strength of leg protein gels; no significant difference was observed for breast gels. Overall, pH 5.75 was suitable for forming strong breast and leg protein gels, whereas pH 5.50 and 6.00 were detrimental for gel formation of breast and leg proteins, respectively. Variations in the gelation behavior of duck breast versus leg protein gelation are characteristic of differences in fiber composition of the muscle types.     

Changes in Protein Solubility and Gelation Properties of Chicken Myofibrils during Storage

The effect of storage on protein solubility and heat-induced gelation properties of chicken hen breast and leg myofibrils was investigated. Myofibrils suspended in 0.6M NaCl, pH 6.0, showed increasing protein solubility, viscosity, gel strength and water holding capacity with storage at 4°C. However, the effect of storage was most dramatic only during the initial 10 hr for all of the parameters studied. The relative distribution of the proteins comprising the salt soluble protein (SSP) extract changed during storage. Although storage had little effect on breast SSP, it was detrimental to leg SSP gelation. Breast myofibril suspensions, for all storage times, contained a greater amount of SSP and had better gelation properties than leg myofibril suspensions.     

Functional Properties of Myofibrillar Proteins from Cold-Shortened and Thaw-Rigor Bovine Muscles

Prerigor bovine sternomandibularis muscles were stored at 15, 0 and ?29°C to examine cold-shortening and thaw-rigor effects on myofibrillar protein extractability and gelation properties of myofibrils and salt-soluble protein (SSP). Frozen muscle that underwent severe contraction at thawing showed greater protein extractability (35%) than muscles stored at 0 and 15°C (27% extractability). Of the three tempered muscles, thaw-rigor muscle produced the strongest myofibril gel and cold-shortened muscle formed the most elastic SSP gel as determined by dynamic shear and penetration measurements. However, thermally induced changes in gel viscoelastic moduli for all protein samples followed similar patterns. Results indicated that physicochemical changes accompanying muscle contraction affected protein network formation during gelation.     

Thermal Gelation Properties of Protein Fractions from Pork and Chicken Breast Muscles

Thermal gelation properties of myosin, actin, myofibrils (MF), sarcoplasmic protein (SP) and connective tissue (CTS) from pork semimem-branosus and chicken breast (CB) were evaluated. Gels were prepared at pH 6.0, 2% NaCl and cooked to 70°C at 0.7°C/min. Pork myosin had a higher gel strength and a lower cooking loss than CB myosin at 7% protein. Actin from both species did not form a measurable gel. MF gels from pork and CB had the lowest cooking loss while CTS and SP had the highest cooking loss. Difference in gel strength between muscle and MF+SP+CTS at 7% protein was not consistent with that at 10% protein.     

Development of a Test to Predict Gelation Properties of Raw Turkey Muscle Proteins

A method for extraction and fractionation of muscle proteins into five fractions based on salt (NaCl) solubility was developed. The influence of protein extractability, solubility, muscle pH and total protein on gelation was investigated. Shear stress (gel strength) and shear strain (gel deformability) at failure of cooked (70°C) comminuted turkey breast gels were correlated with the 10 min protein extract and proteins soluble in 0.30–0.35M NaCl. Shear strain was correlated with muscle pH and shear stress was sensitive to total protein. Meat pH and the extraction/fraction method can be used on raw meat to indicate functional properties related to texture of cooked meat.     

Thermal Transitions of Salt-soluble Proteins from Pre- and Postrigor Chicken Muscles

Salt-soluble protein (SSP) was extracted from pre- and postrigor chicken muscles at various pH values, and protein thermal denaturation was studied using several techniques. Heating at 1°C/min from 20 to 70°C induced a three- to fourfold increase in breast and leg hydrophobicity. Differential scanning calorimetry of breast and leg SSP showed a major transition occurring within the range 55 to 64°C, with the value dependent on rigor state and pH. Protein-protein association, as measured by turbidity change upon heating, underwent two transitions for leg SSP and two or three for breast SSP. The specific transition temperature and rate were dependent on pH, muscle type and rigor state. However, muscle type and pH had a greater effect than muscle rigor state on SSP denaturation.     

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.     

Setting Response of Alaska Pollock Surimi Compared with Beef Myofibrils

Physicochemical properties of surimi after preincubation at 25–50°C and beef myofibrils at 25–60°C for up to 8 hr prior to cooking at 80°C for 20 min were evaluated by a torsion test and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Shear stress and true shear strain of surimi were more sensitive to pH changes than beef myofibrils. Maximum gel strength was found at = pH 7 for surimi and pH 6 for beef myofibrils. The myofibrils showed no setting effect at any preincubation temperatures examined, while surimi showed an optimum setting effect at 25°C. Incorporation of beef myofibrils into surimi resulted in decrease of shear stress and true shear strain values.     

Thermally Induced Interactions and Gelation of Combined Myofibrillar Protein from White and Red Broiler Muscles

The gelling properties of broiler myofibrillar protein were studied by determining protein-protein interactions during heating. Breast and leg salt-soluble protein (SSP) showed 1–3 transitions in protein-protein interactions within pH 5.5–6.5. The maximum transition temperatures of leg SSP decreased when leg SSP was mixed with breast SSP. The combined breast/leg myofibrils formed stronger gels than leg myofibrils alone at pH ≥ 6.0, and stronger gels than breast myofibrils alone at pH < 6.0. The results suggest that interactions existed between breast and leg myofibrillar proteins, and the transitions in these interactions were useful for predicting gel strength of the combined breast/ leg myofibrils.     

猪腿纤维蛋白的热致胶凝与功能性质(英文)

本实验探讨了蛋白浓度和 pH 值对猪腿纤维蛋白的溶解度、凝胶强度、蒸煮失重以及热致胶凝性质的影响。在 0.6mol/L、pH6.0 的 NaCl 溶液中,纤维蛋白的胶凝性最强,凝胶强度随着蛋白浓度的增加而增加。然而,蛋白浓度的增加对蒸煮失重和蛋白质溶解度产生不利影响。猪腿纤维蛋白在 4℃贮存一段时间后,其溶解度有所增加。实验结果表明:pH 值对猪腿纤维蛋白的溶解度、凝胶强度、蒸煮失重和粘弹性都有一定的影响。在 pH6.0 时,蛋白的凝胶强度最大,而在 pH7.0 时,蛋白溶解度最大,蒸煮失重最小。     

Storage Stability of Antioxidant-Washed Myofibrils From Chicken White and Red Muscle

Oxidation and gel-forming ability of chicken white (breast) and red (leg) muscle myofibrillar proteins during storage at 0°C were examined. Breast myofibril gels exhibited greater shear moduli than leg myofibril gels throughout 8 days storage. Shear moduli of both breast and leg gels in the intermediate temperature zone (45–55°C) decreased during storage, but at >55°C, they either increased or remained unchanged. Lipid oxidation was inhibited by washing myofibrils with antioxidants propyl gal-late, ascorbate, and tripolyphosphate. However, these antioxidants did not affect the content of protein carbonyls, and only slightly decreased the amine content during storage. Storage affected the kinetic process of myofibril gelation independently of antioxidant treatments.     

Protein extractability and thermal gel formability of myofibrils isolated from skeletal and cardiac muscles at different post-mortem periods

The effects of the post-mortem ageing period on the extractability of myofibrillar proteins from pork cardiac and rabbit skeletal muscles under various conditions of pH and ionic strength were studied with particular reference to the changes in the solubility of individual myofibrillar proteins and their denaturation characteristics. The ultimate influence of these changes on the heat-induced gel forming ability of myofibrils isolated from cardiac and skeletal muscles at different post-mortem stages was also investigated. Results showed that pork cardiac myofibrils always exhibited lower solubility than those from rabbit skeletal muscles under identical conditions of pH, ionic strength and temperature. SDS-PAGE profiles indicated several quantitative differences in the relative proportion of individual protein species present in cardiac and skeletal myofibrils. The solubility of various proteins present in myofibrils was also affected differently on heating in 0-1 and 0-6 _M NaCl solution at various pH values. Thermal denaturation of cardiac myofibrils occurred at about 10°C higher than that of skeletal myofibrils as revealed by differential scanning calorimetry. Cardiac myofibrils formed much weaker heat-induced gels than those produced by skeletal myofibrils under identical conditions of temperature, pH, ionic strength and protein content.     

Thermal Aggregation Properties of Duck Salt-Soluble Proteins at Selected pH Values

Thermal aggregation properties of duck breast and leg salt-soluble proteins (SSP) were studied at pH 5.50, 5.75 and 6.00. At pH 5.50, a major transition for breast was observed at 60.3°C and for leg at 41.8°C. At pH 5.75, major transitions at 44.6 and 43.2°C were obtained, respectively, for the breast and leg SSP. Three transitions at 46.0, 53.0 and 59.0°C were exhibited by breast SSP at pH 6.00, whereas only two major transitions at 47.4 and 54.0°C were identified in leg SSP. Changes in transition peak heights and shifts in transition temperatures as a result of pH changes indicated that, depending on fiber type, pH may enhance or suppress the aggregation behavior of specific constituents of the myosin/actomyosin complex, thereby altering the overall aggregation pattern of the protein preparation.     

Effect of feed texture, meal frequency and pre-slaughter fasting on carcass and meat quality, and urinary cortisol in pigs

The gelation characteristics of myofibrillar proteins are indicative of meat product texture. Defining the performance of myofibrillar proteins during gelation is beneficial in maintaining quality and developing processed meat products and processes. This study investigates the impact of pH on viscoelastic properties of porcine myofibrillar proteins prepared from different muscles (semimembranosus (SM), longissimus dorsi (LD) and psoas major (PM)) during heat-induced gelation. Dynamic rheological properties were measured while heating at 1 °C/min from 20 to 85 °C, followed by a holding phase at 85 °C for 3 min and a cooling phase from 85 to 5 °C at a rate of 5 °C/min. Storage modulus (G′, the elastic response of the gelling material) increased as gel formation occurred, but decreased after reaching the temperature of myosin denaturation (52 °C) until approximately 60 °C when the gel strength increased again. This resulted in a peak and depression in the thermogram. Following 60 °C, the treatments maintained observed trends in gel strength, showing SM myofibrils produced the strongest gels. Myofibrillar protein from SM and PM formed stronger gels at pH 6.0 than at pH 6.5. Differences may be attributed to subtle variations in their protein profile related to muscle type or postmortem metabolism. Significant correlations were determined between G′ at 57, 72, 85 and 5 °C, indicating that changes affecting gel strength took effect prior to 57 °C. Muscle type was found to influence water-holding capacity to a greater degree than pH.     

Thermal Gelation of Pork, Beef, Fish, Chicken and Turkey Muscles as Affected by Heating Rate and pH

Effects of heating rate (3°C or 0.7°C/min) and pH (5.5, 6.0, 6.5, or 7.0) on thermal gelation properties of different muscle systems were evaluated (10% protein, 2% NaCl) using pork, beef, fish, and chicken and turkey (breast and thigh) muscles. Results indicated that, at pH 6.5 and 7.0, force required to rupture the gel (Pf), force required to move plunger through the gel (Fp), and viscosity index (Ni), using a slow heating rate, were higher than with rapid heating. All muscles (except breast muscles with the slow heating rate) yielded higher (P<0.05) gel strength (Fp, Pf) at pH 6.0 than at the other pHs.     

Effect of Extraction Conditions on the Extractability of Winged Bean (Psophocarpus tetragonolobus (L) DC) Proteins

Protein extractability from defatted winged bean flour was studied under various conditions of pH (2, 4, 6, 8, 10, 12), temperature (15°, 30°, 45°C) and time (10, 20, 30 min). Results indicated that protein extractability was strongly pH dependent. Maximum protein extract-ability was attained at pH 12 while the minimum extractability occurred at pH 4. Protein extractability was not significantly affected at the various temperature and time combinations; however, when extraction time was extended (at 15 min increments) from 30 min to 120 min, significantly higher (15%) protein was extracted at 30°C after an additional 60 min. Increased solvent-to-flour ratios resulted in increased protein extractability, but increased salt (NaCl and CaCl₂) concentrations (1M) decreased extractability.     

Thermally Induced Changes in Protein Extractability of Postrigor Turkey Breast Meat Measured by Two Methods

Extractability of sarcoplasmic and myofibrillar proteins was reduced in postrigor turkey breast meat held at 40 °C for as short as 30 min. These reductions in protein extractability were successfully detected, using either a filtration-based methodology or one based on centrifugation. However, the coefficient of variation for the filtration method was as much as 4 times greater than for centrifugation. Additionally, the filtration method overestimated sarcoplasmic protein extractability due to the inability to exclude myofibrillar proteins. Centrifugation results indicated the extractability of proteins in 0.55 M KCl was reduced to 52% of controls for samples held at 40 °C for 120 min. Additionally, holding postrigor turkey breast muscle at 40 °C resulted in increased myosin degradation.     

Rapid Heating of Alaska Pollock and Chicken Breast Myofibrillar Proteins as Affecting Gel Rheological Properties

Surimi seafoods (fish/poikilotherm protein) in the U.S.A. are typically cooked rapidly to 90+°C, while comminuted products made from land animals (meat/homeotherm protein) are purposely cooked much more slowly, and to lower endpoint temperatures (near 70 °C). We studied heating rate (0.5, 25, or 90 °C/min) and endpoint temperature (45 to 90 °C) effects on rheological properties (fracture, small strain) of washed myofibril gels derived from fish (Alaska pollock) compared with chicken breast at a common pH (6.75). This was contrasted with published data on gelation kinetics of chicken myosin over the same temperature range. Heating rate had no effect on fracture properties of fish gels but slow heating did yield somewhat stronger, but not more deformable, chicken gels. Maximum gel strength by rapid heating could be achieved within 5 min holding after less than 1 min heating time. Dynamic testing by small strain revealed poor correspondence of the present data to that published for gelling response of chicken breast myosin in the same temperature range. The common practice of reporting small‐strain rheological parameters measured at the endpoint temperature was also shown to be misleading, since upon cooling, there was much less difference in rigidity between rapidly and slowly heated gels for either species.     

Heat-induced Gelation of Myofibrillar Proteins and Sausages: Effect of Blood Plasma and Globin

The gelation of meat myofibrils and sausages was monitored during heating with and without added blood globin and plasma by the dynamic rheological method. During heating of beef myofibrils (pH 6.5; prot conc 6.0%) the storage modulus (G') reached a minimum at 47.7°C, decreased on further heating, and increased above 53°C. At higher pH (6.9) the G’value was lower and the magnitude of tanδ increased substantially between 37 and 42°C. Addition of blood globin and plasma changed the thermal gelation of myofibrils. During heating of control and protein-supplemented sausages, we observed two minor peaks in storage modulus in the range 40–55°C and a steep increase at 55–80°C. The storage modulus of low fat sausages, where 25% of meat was replaced by globin or plasma, was greater than that of control sausages.     

The effect of pH and calcium ion on rheological behaviour of β‐lactoglobulin‐basil seed gum mixed gels

Effect of pH (4.5–7.5) and Ca²⁺ (0.01–0.5 m ) on gelation of single and mixed systems of 10% β‐lactoglobulin (BLG) and 1% basil seed gum (BSG) was investigated. The gelling point of BLG and BSG gels was strongly pH‐dependent, and stiffer gels formed at higher pH. The BLG gels were formed upon heating to 90 °C and reinforced on cooling to 20 °C; however, the gelation of BSG occurred at temperatures below 70 °C. By increasing Ca²⁺ concentration, storage modulus of BLG and BSG gels were increased, although pH had a greater effect than Ca²⁺. In contrast, mixed systems showed two distinct types of behaviour: BLG gel formation and BSG network, suggesting that phase‐separated gels were formed. In addition, higher strength was obtained for BLG‐BSG mixture at higher Ca²⁺ concentration.