Thermal Properties of Proteins in Chicken Broiler Tissues

The thermal behavior of breast and thigh muscles, blood and skin tissues of chicken broilers was evaluated by differential scanning calorimetry (DSC). Onset temperature of transition (T_o), maximum thermal transition (T_max) temperatures, and denaturation enthalpy (ΔH) were evaluated. Breast muscle exhibited a complex thermogram with five endothermic transitions at 57°C, 63°C, 67°C, 73°C, and 78°C at a heating rate of 10°C/min. Thigh muscle exhibited only three major transitions at 60°C, 66°C, and 76°C. Thermal curves of isolated protein fractions indicated that the thermal transitions in muscle corresponded to the denaturation of myosin, sarcoplasmic proteins, collagen and F-actin. An increase in the heating rate from 1.0° to 40°C/min significantly elevated the onset temperature of transition and major transition temperatures, as well as the enthalpy of denaturation. Enthalpy of the muscle system heated to various end-point temperatures, cooled and reheated, showed that myosin was completely denatured at 60°C, sarcoplasmic proteins at 70°C and actin at 80°C.     

Differential scanning calorimetric studies of muscle and its constituent proteins

Rabbit muscle and its constituent proteins were investigated by differential scanning calorimetry (d.s.c.). Post-rigor muscle yielded a complex thermogram comprising at least three endothermic transitions with T_max values of 60, 67 and 80°C. Comparison with the purified proteins or fractions indicated that these transitions corresponded to denaturation of myosin, sarcoplasmic proteins and actin respectively. In addition to these endothermic transitions, pre-rigor muscle produced a single large exotherm of T_max 54°C. The evidence suggested that this transition was closely linked with the process of contraction.     

Effect of Sodium Chloride and Phosphates on the Thermal Properties of Chicken Meat Proteins

Maximum thermal transition (T_max) and denaturation enthalpy (ΔH) of water-washed myofibrils and finely cut chicken breast muscle, treated with 1–4% NaCl and/or 0.25–1% of either pyrophosphate (PP) or tripolyphosphate (TPP), were monitored by differential scanning calorimetry. Increasing the concentration of NaCl destabilized the heat resistance of the proteins in water-washed myofibrils and in meat specimens. Actin showed the greatest reduction of T_max, a 16°C decline in the presence of 4% NaCl. In a meat system, the addition of 4% NaCl resulted in one T_max instead of five transitions, as seen in untreated meat. The presence of PP and TPP, especially in concentrations of 0.25 and 0.50%, enhanced the thermal stability of myosin. Changes in denaturation temperatures of proteins were accompanied by corresponding changes in AH.     

A DSC study on the effects of various maltodextrins and sucrose on protein changes in frozen‐stored minced blue whiting muscle

A DSC heat denaturation study on the effects of various maltodextrins and sucrose on protein changes in minced blue whiting muscle during frozen storage at −10 and −20 °C was carried out. All maltodextrins slowed down the decreases in the denaturation enthalpies (ΔH_d) ascribed to myosin and actin, making evident a noticeable effectiveness against protein denaturation, especially at −20 °C. Sucrose was as effective as maltodextrins at −20 °C, but was the least effective treatment at −10 °C. Significant correlations between both ΔH_ds and either protein solubility or formaldehyde production were found at each storage temperature. A low protein sensitivity to the small amounts of formaldehyde produced during the first weeks of storage and errors associated with the determination of enthalpies led to poorer correlations at −20 °C. Maximum denaturation temperatures (T_max) correlated with protein solubility only at −20 °C. No clear relationship between either T_max and the effectiveness of cryostabilisation was found, as T_max also depends on the effectiveness of the treatments against the thermal denaturation of proteins. © 2001 Society of Chemical Industry     

Effects of carrageenan on thermal stability of proteins from chicken thigh and breast muscles

Thermal stability of ground chicken meat and myofibrillar proteins mixed with κ-, ι-, and λ-carrageenan (CGN) at different NaCl concentrations was investigated with differential scanning calorimetry. Three transitions, characteristic of myosin head (63.3, 62.2°C), sarcoplasmic proteins/myosin tail (67.7, 68.6°C), and actin (78.3, 81.4°C), were observed for nontreated thigh and breast muscles, respectively. The influence of CGNs on the thermal transitions was dependent on salt concentrations. κ-CGN with 2.5% NaCl decreased (P<0.05) transition temperature (T_max) of thigh myosin head and actin, while all three CGNs with or without 2.5% salt decreased (P<0.05) T_max for breast actin. Total enthalpy of denaturation decreased slightly in the presence of κ-CGN for thigh muscles only. The gum effects on myofibril isolates were variable and were salt-dependent. The results suggested molecular interactions between the gums and meat proteins, but the response of the specific proteins to gums appeared to be muscle type-dependent.     

Gelatinization Characteristics of Starch from du,wx, ae,and ae wx Endosperm of Sweet Corn Inbred la5125

Starch gelatinization in excess water was studied by differential scanning calorimetry for the mutants dull (du), waxy (wx), and amylose extender (ae), and the double mutant amylose-extender, waxy (ae wx) from the Ia5125 sweet corn inbred background. Onset temperature (T_o), peak temperature (T_max), and enthalpy (ΔH) were determined. For du and wx starches T_max was within 1°C of the value for the normal starch (T_max = 69.4°C). For starches from ae and ae wx mutants, T_max was 7–8°C higher than the normal starch. The highest enthalpies were observed for wx (3.26 cal/g) and ae wx (3.39 cal/g) starches; ae (2.93 cal/g) and normal (2.52 cal/g) starches were intermediate, and du (2.32 cal/g) starch had the lowest enthalpy. The endotherm of the ae starch was completed at just above 100°C, in distinction to reports for ae mutants from dent lines. Although the ae wx endotherm occurred at a higher temperature than the wx, the endotherm was sharpened relative to the ae endotherm, and was complete at 90°C.     

Influence of gender and spawning on thermal stability and proteolytic degradation of proteins in Australian red claw crayfish (Cherax quadricarinatus) muscle stored at 2 °C

Thermal stability and proteolytic degradation of male (M), nonspawning female (F) and spawning female (SF) red claw crayfish (Cherax quadricarinatus) muscle proteins during refrigerated storage (2 °C) were investigated. The thermal transition temperatures (T_max) of myosin and actin remained relatively constant during storage, but their enthalpies of denaturation (ΔH) increased, especially in SF samples. SF muscle proteins were more heat‐stable (greater T_max and ΔH values, P < 0.05) than M and F muscle proteins. Protein degradation occurred in all muscle groups, more rapidly in M and F muscles than in SF muscle. The diminishments of a 69‐kDa component and troponin‐I and the appearance of a 55‐kDa polypeptide represented the most salient proteolytic changes. The results suggested that the spawning status was a more significant factor than gender in affecting the quality of red claw muscle proteins and their changes during refrigerated storage.     

Phase Transitions and Unfreezable Water Content of Carrots, Reindeer Meat and White Bread Studied using Differential Scanning Calorimetry

Differential scanning calorimetry was used to measure the phase transitions and unfreezable water of carrots, reindeer meat, and white bread. The incipient melting point (T_im), incipient intensive melting point (T′_im), the onset temperature of melting (T_m), latent heat of melting (ΔH_m), specific heat (C_p) and enthalpy (ΔH) were determined from the melting curves. T′_im, T_mΔH_m and ΔH and the unfreezable water were found to be functions of moisture. The T_im, temperatures were ? 39°C, ?33°C, ?40°C; T′_im, ?11.8°C, ?13.3°C ?17.3°C T_m, ? 3.4°C, ? 3.1°C, ? 12.2°C for carrot, reindeer meat, and white bread, respectively. The unfreezable water was 8.3% for carrots, 15.1% for reindeer meat, and 22.5% for white bread, determined from ΔH_m and 3.4%, 6.4% and 2.9%, determined from ΔH. The lowest water detectable from ΔH_m was 26.4% and from ΔH 3.6%.     

Extractability and thermal stability of frozen hake (Merluccius merluccius) fillets stored at −10 and −30 °C

The relationship between thermal stability changes and functionality loss was monitored in hake muscle fillets stored for 40 weeks at ?10 and ?30 °C. The evolution of changes in apparent viscosity, dimethylamine formation and extractability of muscle proteins in NaCl, sodium dodecyl sulphate (SDS) or SDS plus mercaptoethanol showed drastic differences as a function of temperature. At the higher storage temperature, both myosin heavy chain and collagen were the most severely unextracted in salt and SDS solutions, with actin becoming unextractable at the end of storage. Differential scanning calorimetry showed differences with storage time and temperature in both onset temperature and thermal denaturation enthalpy, mostly affecting the myosin transitions. Some protein denaturation occurred with little or no functionality loss. A considerably high fraction of hake muscle proteins remained in the native‐like condition even at the higher frozen storage temperature. In these conditions both apparent viscosity and myosin and actin extractability in NaCl were very low. © 2002 Society of Chemical Industry     

Thermal denaturation of proteins in Post rigor muscle tissue as studied by differential scanning calorimetry

Post rigor bovine M. semimembranosus was analysed by differential scanning calorimetry (d.s.c.). After extractive removal of sarcoplasmic proteins, subsequent pH adjustment and manual connective tissue removal, d.s.c. yielded reproducible thermograms which permitted investigation of the individual major myofibrillar proteins in various pH and salt environments without prior isolation. The positions of two major peaks, interpreted as myosin transitions, proved to be strongly pH dependent. At pH 5.4, the peak maxima occurred at 58 and 65°C, respectively, at a heating rate of 10°C min-¹. Above pH 6.5 their order of denaturation was reversed. In the pH range 5.4–6.5 the peak ascribed to actin had its maximum near 80°C in intact muscle. Above this pH range it was displaced to lower temperature. The thermal stability of actin was studied after treatment of the muscle tissue with different salt solutions. At equal ionic strengths (μ = 0.15) at pH 5.5, calcium chloride and sodium chloride caused 6.5°C and 4°C displacement to lower temperature, respectively. The thermograms of bovine semimembranosus muscle were compared to those of two red and two white muscle types (bovine cardiac and rabbit soleus muscles, chicken breast and rabbit semimembranosus muscles, respectively) at two pH levels. Greater myosin differences were found between red and white muscles than between muscles from different animal species. All muscles gave similar actin transitions, with exception of the heart muscle where the actin peak appeared at 3 °C lower temperature. The necessity of a strict pH control in order to obtain reproducible muscle thermograms is demonstrated.     

Preliminary studies to determine the chaperoning properties of bovine casein and crystallin proteins at reducing beef muscle protein aggregation during heating

The ability of small heat shock proteins (sHSP) at preventing the aggregation and precipitation of unfolded and misfolded proteins because of changes in pH and temperature is widely recognised. The performance of sHSP from bovine lens extract at protecting sarcoplasmic proteins from heat induced denaturation and aggregation was compared with other chaperones including bovine serum albumin, α_s‐casein, β‐casein and a synthetic peptide based upon αA‐crystallin (AAC). Beef sarcoplasmic proteins were heated in the presence or absence of exogenous chaperone and the solubility, surface hydrophobicity and enzymatic activities of the sarcoplasmic proteins was determined. Lens extract prevented the aggregation of sarcoplasmic proteins, maintaining solubility and clarity up to 65 °C relative to 60 °C for β‐casein. By contrast, α_s‐ and β‐casein proteins protected the activity of endogenous enzymes at temperatures between 37 °C and 52 °C, unlike lens sHSP. Our findings support the addition of casein proteins as potential thermal stabilisers of meat proteins in food systems.     

Thermal Denaturation in Fish Muscle Proteins During Gelling: Effect of Spawning Condition

We studied thermal denaturation of myofibrillar proteins from pre-and post-spawning hake by differential scanning calorimetry (DSC), and evaluated denaturation kinetics under both conditions. The denaturation enthalpies of all pre-spawning fish muscle extracts were less than those from post-spawning. The area under the DSC thermogram corresponding to myosin denaturation was smaller in myofibrillar extracts from pre-spawning than from post-spawning hake, while the areas corresponding to denaturation of actin were similar. Between 40 and 55°C the myosin denaturation rates were greater for post-spawning than for pre-spawning hake. Both entalphies and kinetic data indicated proteins of fish in a better biological condition (post-spawned) denature more rapidly and completely.     

Physicochemical and Functional Properties of Dry and Wet Milling Products of Red Cowpeas

Physicochemical and functional properties of dry- and wet-milled red cowpea flour, protein and starch were evaluated. Bulk density of drymilled red cowpea protein was lower than that of wet-milled protein isolate. Dry-milled starch was darker than wet-milled starch. Gelatinization temperature of starch (64–68–74°C) was quite similar to that of mung bean starch. At water to red cowpea starch ratios of 3:1 and 2:1, DSC thermograms showed a single endotherm with T_o of 68.5–69.0°C, T_p of 73.0–73.5°C, T_m of 79.5–80.0°C, and –ΔH of 4.0–4.6 cal/g starch. Pasting properties of red cowpea starch showed a type C amylogram, similar to mung bean starch. By mixing various quantities of red cowpea starch to tapioca starch pasting properties of the latter could be varied. Water and oil absorptions of cowpea flours increased with the increase in protein contents, as did their emulsifying activity and foaming properties. Emulsion and foam stabilities were quite similar among all the red cowpea products, except for protein isolate which were considerably lower, likely due to a greater degree of protein denaturation during precipitation and drying of the isolate. Composite flours made from mixing wheat and red cowpea flours exhibited dough mixing properties indicative of their potential use in baked products.     

A heat denaturation study of the 11S globulin in soybean seeds

When the 11S globulin, one of the major storage proteins in soybean seeds (Glycine max), was heated at 0·5 ionic strength, the denaturation temperature was biologically estimated to be about 10 degrees higher than that at 0·1 ionic strength. The results also coincided well with those obtained by differential scanning calorimetry. The heat denaturation temperatures of the protein obtained by differential scanning calorimetry were estimated to be 78·1°C and 89·6°C at 0·1 and 0·5 ionic strength respectively. The enthalpies of heat denaturation were 2·0 cal/g and 3·2cal/g at 0·1 and 0·5 ionic strength, respectively. Correlation was not observed between the heat stability at high ionic strength and the content of the ordered secondary structure or a dissociation-association reaction of the protein with change of ionic strength. However, increase of the hydrophobic region at high ionic strength indicated the possibility of stabilisation of the quaternary structure of the 11S globulin by hydrophobic bonding during heat denaturation.     

Differential Scanning Calorimetry of Beef Muscle: Influence of Sarcomere Length

Contraction state of beef muscle at onset of rigor influences tenderness of cooked meat. Loss in tenderness during cooking has been related, through use of differential scanning calorimetry (DSC), to thermal denaturation of myofibrillar proteins. Contraction of beef sternomandibularis muscle was controlled at sarcomere lengths of 2.4, 2.1, 1.9, 1.7, and 1.4 μm. Samples were scanned from 25- 105°C at 10°C/min; ΔH (change in heat of transition) between 45° and 92°C dropped from ca. 4 J/g muscle at 2.4 μm to ca. 3 J/g at 1.4 μm. This difference (P < 0.05) amounts to less than 1% of the total energy resuired to heat meat from 45° to 92°C. The decrease is attributed to a greater actomyosin contribution to the overall thermal curve resulting from increased overlap of the filaments.     

Influence of Sodium, Potassium and Magnesium Chloride on Thermal Properties of Beef Muscle

Sodium, potassium and magnesium chloride, at 1.25, 2.50 and 5.00%, were studied using differential scanning calorimetry. Increasing NaCl resulted in decrease in myosin transition temperature (T₁, first transition) and enthalpy (H₁); both showed significant (P<0.05) linear response. The sarcoplasmic proteins and collagen denaturation temperature (T₂, second transition) increased significantly over the control when 1.25% NaCl was added, but were the same as control when 2.5% and 5.0% were used. Actin denaturation temperature (T₃, third transition) tended to increase when NaCl was added, but enthalpy decreased. Potassium chloride showed similar effects to NaCl on T₁, T₂, H₁ and H₃. Increasing magnesium chloride had much more pronounced effect on decreasing second enthalpy compared to the monovalent salts. At 5% MgCl₂ T₁ increased significantly.     

Differential Scanning Calorimetry of Beef Muscle: Influence of Postmortem Conditioning

Differential scanning calorimetry (DSC) was used to follow the changes in the endothermic transitions of beef muscle during conditioning. Sternomandibularis muscle held at 5°C from 2–8 days postmortem resulted in a significant (P < 0.05) drop in the total heat of transition (ΔH) from 3.8 to 3.0 J/g. The myosin transition decreased from 57.8° to 55.2°C while the actin transition increased from 81.8° to 83.2°C (P < 0.05). Storage time and temperature were varied to generate a response surface of thermal data for psoas major and semimembraneosus muscle. The decrease in °H of psoas major was optimal between 10° and 13°C. Total ΔH of semimembraneosus (3.9 J/g) was significantly greater (P < 0.05) than that of psoas major (3.4 J/g).     

The effect of starch gelatinization and solute concentrations on T g′ of starch model system

The effect of starch gelatinization on glass transitions in a starch/water model system and how the concentrations of added solutes (sucrose and sodium chloride) affect the glass transition temperatures of the gelatinized starch solution was investigated. The starch suspension samples were heat treated in a Differential Scanning Calorimeter (DSC) under different time and temperature regimes to achieve different degrees of gelatinization. The gelatinization characteristics (onset, peak and end temperatures and enthalpy) and the glass transition values of a potato starch were determined using the DSC. The results showed that the starch concentrations had no effect on gelatinization characteristics and the T_g′ of the gelatinized potato starch but had clearly increased their ΔC_p in the T_g′ region. Annealing at a temperature slightly below the T_g′ of −5 °C, led to maximal freeze‐concentration in the total/partial gelatinized starch and a higher T_g′ value at about −3 °C was obtained. The T_g′ values of the totally gelatinized starch samples were slightly lower than those of partially gelatinized samples. The T_g′ of the gelatinized starch decreased with increasing concentrations of sucrose or sodium chloride. Sodium chloride had a stronger depressing effect on T_g′ than sucrose. © 2000 Society of Chemical Industry     

HAPTENIC CARBOHYDRATES AFFECT THE THERMAL DENATURATION OF SOYBEAN LECTIN

The effect of haptenic carbohydrates, N-acetyl-galactosamine and galactose, on soybean agglutinin (SBA) thermal denaturation was measured by differential scanning calorimetry (DSC) and batch heating in an oil bath. Thermodynamic parameters were determined by scanning from 30 to 11OC, at 1C/min. Lectin activity was measured by a hemagglutination test after heating at 80, 85, 90 and 95C for 5, 10, 15 and 20 min. Soybean lectin denaturation was an irreversible process with ΔH^±= 120 kcal/mol that was significantly reduced by carbohydrates, and it was a carbohydrate concentration dependent phenomenon. In addition, haptenic carbohydrates induced an increase of the T_max and T_tr of SBA denaturation when compared with soybean lectin solution alone. The loss of lectin activity was faster in absence of haptenic carbohydrates than those obtained from solutions with the specific sugars. It was concluded that haptenic sugars protected the SBA against denaturation.     

Effects of NaCl Concentration and Potassium Chloride Substitutions on the Thermal Properties and Lipid Oxidation of Dry‐Cured Pork

The thermal properties of cured meat are important for determining storage life and nutritional quality. However, few studies have focused on the thermal properties of dry‐cured pork, particularly in relation to salt level and type. In order to study the thermal properties of dry‐cured pork, we used differential scanning calorimetry (DSC) to evaluate the net heat energy (enthalpy, ΔH), onset (T_onset), and maximum (T_max) temperatures of different pork cuts salted with mixtures of chloride (NaCl and KCl) salts within the curing and ripening temperature range. Within the curing temperature range (?5 to 20 °C), the T_onset, T_max, and ΔH of cured meat treated with different NaCl : KCl mixtures were generally lower than for fresh meat, which indicates that the addition of NaCl or KCl can reduce the melting of lipids and water (especially lipids), in different pork cuts. Within the ripening temperature range (5 to 50 °C), heat absorption peaks in belly and leg cuts were between 29 and 33 °C. However, no obvious heat absorption peak was found in loin cuts. Compared to non‐KCl substitutions, a slightly higher KCl substitution could significantly (P < 0.05) enhance ΔH values of dry‐cured belly and leg cuts. The likely cause of this phenomenon is that high KCl substitutions promote lipid oxidation (r = 0.98, for belly; r = 0.95, for leg cuts). Therefore, KCl substitution should be no more than 30% (wt/wt), especially for high lipid pork, to prevent excessive melting and oxidation of lipids during the dry‐curing process.