Influence of pH on rheological properties of porcine myofibrillar protein during heat induced gelation

Texture of meat products is dependent on the gelation characteristics of myofibrillar protein. Gaining an understanding of the gelation mechanism of meat gel systems is beneficial for the development of processed meat products as well as maintaining quality in meat products. The aim of this study was to investigate the impact of pH (5.6, 6.0, 6.5, and 7.0) on heat-induced gelation properties of myofibrillar proteins from porcine semimembranosus muscle. Dynamic rheological measurements were taken as the temperature increased by 1°C/min from 20 to 85°C, followed by a holding phase at 85°C for 3min to ensure complete gelation and during a subsequent cooling where the temperature dropped from 85 to 5°C at a rate of 5°C/min. Storage modulus (G') 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 subsequent depression in the data. This depression in the curve was more pronounced with increasing pH. Results indicate protein denaturation and gel formation are pH dependent. Furthermore, rate of gelation appears to influence water-holding capacity.     

Thermal scanning rheology of myofibrillar proteins from muscles of defined fibre type

Emulsion meat products are made with little regard to rheological properties of different muscles. Here the rheology of gels made from three classes of muscle defined by myosin type (fast twitch, slow twitch and heart) are compared. Myofibrillar fractions were prepared from representative bovine muscles-cutaneus trunci, masseter and heart-by a procedure that removed connective tissue, fat and sarcoplasmic proteins. Complicating effects of nongelling agents were thus minimized. Fractions were mixed with NaCl and pyrophosphate at concentrations typical of those used in processed meats. Rigidity and elasticity of the gelling mixtures were monitored during heating from 10 to 84°C over a range of pH values. Several indices of gelation showed that masseter and heart (slow muscle group) gelations were similar to each other but distinct from cutaneus trunci (fast) gelation. Gelation temperature was 10°C lower for fast than slow, perhaps explainable by one of two hypotheses: differential salt extraction or lower thermal stability of fast myosin rod. Cutaneus trunci gels were also more rigid at all pH values. Slow group gels suffered from proteolysis, which was combated with cathepsin inhibitors. For both fast and slow groups, rigidity increased as pH decreased, analogous to results reported for purified myosin in dilute solution. Texture also changed. Below pH 5·7 slow group gels were brittle and granular, with low water-holding capacity. Above that pH, gels were elastic and smooth. The equivalent point for cutaneus trunci gels was pH 5·5. Around pH 7, pyrophosphate had a fluidizing effect at pregelation temperatures, but elasticity data indicated that this ion plays no part in final gelation.     

Effects of electrical stimulation and ageing of beef on the gelation properties and protein extractability of isolated myofibrils

The gelation properties of bovine myofibrils, as evaluated by dynamic rheological measurements, were shown to be very sensitive to the variables investigated: stimulation and/or ageing of the meat used, presence of 5 mM pyrophosphate and 5 mM MgCl₂ (PP) and concentration of NaCl (0·3 or 0·M). Statistical evaluation of final gel storage moduli (determined at 70°C) revealed ageing to have a consistent detrimental effect. Fresh, stimulated processing of meat), gave gels of about 40% lower elasticity (storage modulus) than did non-stimulated myofibrils; when PP was included in the gel-forming mixture no effect from electrical stimulation was seen. In spite of the negative effects observed for gel elasticity, the myofibrils in question displayed enhanced protein extractability prior to heating. Electrophoretic results suggest myosin degradation to be partly responsible.     

Effects of salt reduction on the rheological and gelation properties of beef, pork and poultry meat batters

The gelation and rheological properties of beef, pork and poultry meat batters as affected by salt reduction (2·50, 1·25 and 0·00%) were studied by using a Haake rotational viscometer and a thermal scanning rigidity monitor. Beef batters showed a decrease in shear stress with the decrease in salt levels at both high and low shear rates. Pork batter showed a mixed behavior (no definite trend in shear stress versus shear rate) and the poultry meat batters showed a Bingham pseudoplastic behavior, except for the no-salt treatment. During heating the beef batters showed the highest G values followed by the pork and the poultry meat batters. The rigidity modulus profiles exhibited two major transition temperatures at 47-53°C and at 64-76°C. Beef batter with 2·50% salt developed the highest average G value (16·6 kPa) and the poultry batter with 2·50% salt the lowest (7·3 kPa).     

GELATION KINETICS of MEAT EMULSIONS CONTAINING VARIOUS FILLERS DURING COOKING

A cylindrical shaped thermal scanning rigidity monitor (TSRM) was developed to determine shear rigidity modulus of meat batters during cooking. A meat fatprotein ratio of 1.8, moisture content of 62% and 8.6% filler were used. the fillers were buttermilk powder, corn starch, micro-crystalline cellulose, modified corn starch, modified wheat flour, soy-protein concentrate and whey-protein concentrate. Plots of rigidity modulus versus product-temperature showed two major thermal transitions. the first and most important transition (53 to 61°C) was due to myosin gelation. the second transition (64 to 69°C) was ascribed to the collagen softening. the maximum rigidity-temperature slopes of 0.60 to 1.02 kPa/°C occurred after the first transition.     

Phosphates and antioxidants as cryoprotectants in meat batters

The gelation and rheological properties of minced beef frozen and stored at -18°C for 6 months without additives, with salt (1·5% NaCl), tripolyphosphate (TPP 0·5%), sodium acid pyrophosphate (SAPP 0·5%) and an antioxidant mix (BHA + BHT, 200 ppm) were studied. The relationships between shear rate and shear stress for the different treatments were nonlinear and resembled the Bingham pseudoplastic behaviour. Continuous evaluation of the modulus of rigidity (G) during cooking (0·5°C/min) revealed higher G values for the unfrozen phosphate treatments. Salt addition resulted in significantly lower G values of the stored meat compared to the control. Antioxidant addition retarded some of these effects. Among the phosphates, TPP was the best in maintaining the same G values as the control. Water-holding capacity (after salt addition) was increased after phosphate addition in the unfrozen meat and did not change after storage. The control, NaCl and antioxidant treatments showed an increase in WHC during storage.     

Thermorheological Characteristics of Soybean Protein Isolate

ABSTRACT: Small amplitude oscillation shear measurement was used to study gel rigidity of commercial soy protein isolate (SPI) dispersions during isothermal and non-isothermal heating. Temperature sweep data (20°C to 90°C atheating rate of 1°C/min) of SPI dispersions demonstrated that elastic modulus (G) predominates over viscous component (G') for all concentrations studied. The gelation kinetics of SPI was evaluated by a non-isothermal technique as a function of elastic modulus (G). During experiments, it was observed that a critical concentration of 10% was required to form a true SPI gel. Thermorheological data of 10% and 15% SPI dispersions were adequately fitted by 2nd-order reaction kinetics. The reaction order of gelation was initially calculated by multiple regression technique correlating dG'/dt, G'and temperature, which finally was verified by linear regression of kinetic equation at selected order. Isothermal data of 15% SPI was also followed by 2nd-order reaction kinetics. The activation energy during the isothermal technique was significantly higher than non-isothermal gelation of SPI at same concentration level. Gel strength of the non-isothermally heated SPI sample (15% to 20%) was compared with isothermally heated (90°C for 30 min) one. Higher protein concentration (20%) and isothermal heating exhibited significantly higher gel rigidity while the difference between the 2 processes was insignificant at 15% concentration at a similar condition.     

Oxidative stability of lipids and cholesterol in salame Milano, coppa and Parma ham: dietary supplementation with vitamin E and oleic acid

Spent hen (98 weeks) and broiler (12 weeks) breast and thigh muscles were minced (1 mm orifice diameter) and washed with 0.1% NaCl. A portion of both unwashed and washed mince was mixed with cryoprotectants (CP) at the rate of 4% sucrose, 4% sorbitol, and 0.2% Na-tripolyphosphate to produce surimi and kept frozen at -20°C. The mince and surimi were ground with 3% NaCl and a small amount of water to adjust the final moisture content of 80%. The pastes were stuffed into the sausage casing and heated at 90°C for 15 min to produce gel. The effects of washing, heating and CP on colour composition and thermal gelation properties of hen and broiler minces and surimi were compared. Broiler mince was lighter and less red in colour, higher in protein and lower in moisture, lipid and collagen. Gel strength and breaking strength were higher in spent hen surimi compared to broiler surimi under similar gelation conditions. Gel elasticity, springiness and water retention properties were almost identical in two surimi. Gel quality was markedly deteriorated in spent hen surimi but not so in broiler surimi after 8 weeks frozen-storage. Although CP increased the gel strength of fresh surimi (non-frozen, 0 week storage) from both hen and broiler, they were more effective in broiler surimi than hen surimi in protecting the functional quality of gel.     

Rigidity and Viscosity Changes of Croaker Actomyosin During Thermal Gelation

Two types of thermal scanning rigidity monitors (TSRM) were developed which are nondestructive and capable of monitoring rigidity or viscosity changes during heating of proteins over a wide range of concentrations. Thermal transitions which occur during gelation of croaker actomyosin were studied by these TSRM devices and the Brookfield viscometer during constant rate heating (1°C/min). Gelation of actomyosin occurred only at protein concentrations above 5.5% under these conditions. In plots of rigidity versus temperature, three transitions were observed during gelation, occurring near 38°C 46°C and 60°C. At lower concentrations, only one peak was observed, occurring near 36°C. A relationship between the 36–38°C transition in rheological properties and the high temperature “setting” phenomenon of fish proteins is postulated.     

β-Lactoglobulin Gelation and Modification: Effect of Selected Acidulants and Heating Conditions

ABSTRACT: The effect of acidulant selection, heating temperature, and heating rate on the properties of low-pH β-lactoglobulin (β-Lg) gels and powders derived from these gels was investigated by rheological and microscopic techniques. As isothermal gelation temperature was increased from 75 to 85 °C, gels made with hydrochloric and lactic acid showed more rapid gel formation and increased stress at gel fracture. Thickening and water-holding properties of powders derived from these gels also increased with temperature. Increases in gel strength and derivatized powder functionality appeared to plateau above 85 °C. Gels and derivatized powders prepared with phosphoric acid exhibited attributes similar to samples prepared with HCl and lactic acid at lower temperatures. The ion-specific ability of phosphate to increase denaturation temperature was responsible for the shift in properties of gels made with phosphoric acid. Microscopy revealed temperature effects on network building block size, but variations in rheological properties could not be linked to changes in gel micrographs. Alteration of heating rates from 2.0 to 0.2 °C/min during gelation affected the observed gelation temperature, but had little effect on final gel mechanical properties. Acid selection and gelation temperature offer alternatives to control β-Lg gel strength and the functional properties of instant thickening protein ingredients.     

1,5-glucono-δ-lactone-induced gelation of myofibrillar protein at chilled temperatures

In this study 1,5-glucono-δ-lactone was used to achieve acid-induced gelation of myofibrillar proteins at 4 °C. The characteristics of the myofibrillar gels were investigated by measuring Young's modulus and springiness. The effects of addition of sodium chloride and tetrasodium pyrophosphate on gel characteristics were also studied. Sodium chloride increased the Young's modulus of myofibrillar protein gels in the presence and absence of 1,5-glucono-δ-lactone, while tetrasodium pyrophosphate had no observable effect on the gels until the pH decreased to 4.1, when the Young's modulus was enhanced.     

Rheological changes during thermal processing of low-fat meat emulsions formulated with different texture-modifying ingredients

The rheological behaviour of high-fat (22%) and low-fat (8%) meat emulsions during thermal processing in the presence (3%) of various texture-modifying non-meat ingredients, namely maltodextrin, starch, wheat flour, egg white and apple fibre, was analysed. Rheological properties of emulsions were assessed using non-destructive measurements (thermal scanning rigidity monitor, TSRM). The lower the fat content, the lower were the rigidity values of meat emulsions throughout the temperature range studied. Emulsions made with maltodextrin proved less rigid. Addition of starch and egg white favoured the formation of more rigid structures in low-fat meat emulsions at temperatures over 55 °C. Low-fat meat batters containing wheat flour and apple fibre exhibited the highest rigidity values over the given temperature range. The presence of wheat flour caused variations in the modulus of rigidity at all stages of the thermal gelation process, very similar to those observed in high-fat emulsions.     

Modelling the yield and texture of comminuted pork products using color and temperature. Effect of fat/lean ratio and starch

Practices to control the processing of finely comminuted meat products are proposed. The objective was to test the practical value of both temperature and light reflection measurements made during emulsification as potential indicators of cooking losses and resulting gel texture in pork sausages emulsified within a wide range of temperatures and starch and fat levels. Prior to cooking, pork batters were chopped for different times to ensure final emulsion temperatures ranging from 5 to 50°C. The effects of the fat/lean ratio (0.25 and 0.67) and starch addition (0.8 and 3.2% w:w) on temperature and optical reflection were also investigated. The chopping increased the temperature and decreased the light reflection of fresh meat emulsion. There was no relevant loss of emulsifying capacity at emulsion temperature below 30°C and lightness values over 70 CIE units. The losses and textural parameters of cooked emulsions could be predicted by means of non-linear regression equations based on the temperature and color of the raw emulsion. The determination coefficients obtained ranged from 0.89 to 0.99. The prediction models needed to be fitted to each batter formulation, especially in the presence of reduced levels of gelation agents (meat protein and starch). Lightness was a better predictor than chromaticity, since it decreased constantly with chopping in the range of final emulsion temperatures studied (5-50°C). This confirms previous studies that lightness could be used for monitoring emulsion stability in meat batters.     

Pressure-assisted gelation of chemically modified poultry meat batters

Changes were induced in the characteristics of poultry meat protein using specific chemical modifiers to investigate the effect of pressurization, prior to heating, on gelation, texture and thermal behaviour of meat batters. Values of hardness and chewiness were higher in cooked meat batters treated with urea than in a salt-only sample, but cohesiveness was similar. The β-mercaptoethanol treatment produced a heat-induced gel with very similar properties to the salt-only gel. The rheological behaviours of salt-only and β-mercaptoethanol samples were very similar, but storage modulus values were higher in samples with urea, which accelerated gelation. The pressure-induced reduction of differences in the textural properties of meat batters suggests that hydrophobic interactions play an important role in heat-induced gelation. Differential scanning calorimetry showed that urea clearly destabilized chicken meat batters, while β-mercaptoethanol had very little influence on their thermal behaviour. Pressurization tended to equalize batters and final cooking definitively equalized them.     

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.     

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 Some Protease Inhibitors on Gelation of Squid Muscle

ABSTRACT: The effect of 4 food-grade protease inhibitors–bovine plasma, potato powder, ethylenediamine-tetraacetic acid, and sodium pyrophosphate–on heat gelation of squid (Todaropsis eblanae) muscle was studied. The action of these ingredients was characterized by determining the proteolytic activity in batters containing them and the rheological properties of gels made with them. The gelation profile showed that the setting effect was greatest with pyrophosphate (PPI) and that gel rigidity was highest with bovine plasma (BP). All 4 inhibited proteolytic activity to some extent at 65 °C. BP was the most effective. At 40 °C, only EDTA and PPI were active. Rheologically, the most effective combination was PPI plus bovine plasma in that this combined inhibition of proteolytic activity with gel enhancement.     

How micro-phase separation alters the heating rate effects on globular protein gelation

This study was conducted to determine how the combination of heating rate and pH can be used to alter viscoelastic properties and microstructure of egg white protein and whey protein isolate gels. Protein solutions (1% to 7% w/v protein, pH 3.0 to 8.5) were heated using a range of heating rates (0.2 to 60 °C/min) to achieve a final temperature of 80 °C. The gelation process and viscoelastic properties of formed gels were evaluated using small strain rheology. Single phase or micro-phase separated solution conditions were determined by confocal laser scanning microscopy. In the single phase region, gels prepared by the faster heating rates had the lowest rigidity at 80 °C; however, a common G' was achieved after holding for 4 h at 80 °C . On the other hand, under micro-phase separation conditions, faster heating rates allowed phase separated particles to be frozen in the network prior to precipitation. Thus, gels produced by slower heating rates had lower rigidities than gels produced by faster heating rates. The effect of heating rate appears to depend on if the solution is under single phase or micro-phase separated conditions. PRACTICAL APPLICATION: The effect of heating rate and/or time on protein gel firmness can be explained based on protein charge. When proteins have a high net negative charge and form soluble aggregates, there is no heating rate effect and gels with equal firmness will be formed if given enough time. In contrast, when electrostatic repulsion is low, there is a competition between protein precipitation and gel formation; thus, a faster heating rate produces a firmer gel.     

Role of F-actin in Thermal Gelation of Fish Actomyosin

The thermal gelation processes of the myosin-natural actomyosin system were investigated to determine the role of F-actin in thermal gelation of actomyosin. The dynamic viscoelastic behavior during thermal gelation changed considerably depending on the (F-actin)/ (myosin) ratio. F-actin gave the viscosity to an actomyosin sol but did not affect the elasticity development occurring in the 30 - 46°C range. The decrease in storage modulus in the 46 - 53°C range was directly induced by the presence of F-actin. The gel of myosin alone showed the highest elasticity, while that of myosin containing a small amount of F-actin had the highest elastic modulus.     

Dielectric and thermophysical properties of meat batters over a temperature range of 5-85 °C

Dielectric (dielectric constant (ε(')) and loss factor (ε″)) and thermal (heat capacity (c), thermal conductivity (k) and thermal diffusivity (α))) properties of two meat batters (pork luncheon roll (PLR) and white pudding (WP)) were measured between 5 and 85 °C. Radio frequency (RF) and microwave (MW) ε″ values varied across 5-85 °C (P<0.05). MW ε(') and ε″ values for WP tended to peak at 45 °C and decrease thereafter, whereas for PLR, ε(') and ε″ peaked at 65 °C which appeared to match potato starch gelatinisation within this product. WP and PLR had significantly higher c values at 25 °C, which corresponded to the MP of pork fat. For PLR, an additional c peak was noted at 65 °C, which appeared to correspond to potato starch gelatinisation. At 85 °C, k values were higher (P<0.05) than at 5, 25 and 45 °C but were not higher than values at 65 °C. α values increased with temperature (P<0.05).