EFFECT OF TEMPERATURE, EXOGENOUS CALCIUM AND PH ON THE PROPERTIES OF MUSCLE TISSUE PROTEINS
EFFECT OF TEMPERATURE, EXOGENOUS CALCIUM AND PH ON THE PROPERTIES OF MUSCLE TISSUE PROTEINS
Gaukhar Ilyasova
Biology teacher, №3 IT school after S. Tolybekov,
Kazakhstan, Kyzylorda
ABSTRACT
In this paper described structure of protein molecules, some characteristics of proteins. During experimental part by effecting of temperatures it was destruction of proteins. With prolonged heat treatment, proteins undergo deeper changes associated with the destruction of their macromolecules. At the first stage of changes, functional groups can be split off from protein molecules with the formation of such volatile compounds as ammonia, hydrogen sulfide, hydrogen phosphide, carbon dioxide, etc. Accumulating in the product, they participate in the formation of the taste and aroma of the finished product. During further hydrothermal treatment, proteins are hydrolyzed, while the primary (peptide) bond is broken with the formation of soluble nitrogenous substances of a non-protein nature.
Keywords: proteins, temperature, pH, properties, acidity, hydrogen ions, calcium.
The structure of protein molecules is relatively easy to change under the influence of various physical and chemical factors, while losing a number of original properties, and above all the solubility of proteins. This phenomenon is called denaturation. Under the influence of heat, ultrasound, ultraviolet and ionizing radiation, high pressure, when exposed to salts of heavy metals and other chemicals, surface denaturation of protein molecules occurs - a change in the native spatial quaternary structure, not accompanied by breaking of covalent bonds. In this case, the helix of the polypeptide chain unfolds in space and a disordered tangle is formed [1,2]. Depending on the degree of denaturation, the secondary and tertiary structures of the protein can also be destroyed, which leads to a loss of biological activity. Protein denaturation occurs in the presence of water.
During thermal denaturation (60 - 100 ° C), proteins lose their ability to dissolve in water, salt solutions and organic solvents, and their ability to swell also decreases. The change in protein during thermal denaturation is the more significant, the higher the temperature and duration of heating, and the protein in an aqueous solution denatures faster than in the dried state.
Protein denaturation plays an important role in the manufacture of sausages, the production of fodder flour, the drying of egg powder, blood and blood products, the cooking of meat, and the sterilization of canned meat.
Changes in meat protein during heat treatment affect the technological and quality indicators of finished products. [3]
Destruction of proteins. With prolonged heat treatment, proteins undergo deeper changes associated with the destruction of their macromolecules. At the first stage of changes, functional groups can be split off from protein molecules with the formation of such volatile compounds as ammonia, hydrogen sulfide, hydrogen phosphide, carbon dioxide, etc. Accumulating in the product, they participate in the formation of the taste and aroma of the finished product. During further hydrothermal treatment, proteins are hydrolyzed, while the primary (peptide) bond is broken with the formation of soluble nitrogenous substances of a non-protein nature (for example, the transition of collagen to glutin). The destruction of proteins can be a purposeful culinary treatment that contributes to the intensification of the technological process (the use of enzyme preparations to soften meat, weaken the gluten of the dough, obtain protein hydrolysates, etc.)[4].
EXPERIMENTAL PART
Acidity (pH), due to the presence of hydrogen ions, is an important indicator of meat quality. This figure always increases after slaughter. The pH value of meat affects its microstructure, the development of microflora, the intensity of decay processes and autolytic changes after slaughter, and ultimately on the organoleptic characteristics and the ability of culinary processing.
The shift in the pH of meat to the acidic side triggers the transformation of myofibrillar proteins:
- changes in the permeability of myofibril membranes;
- calcium ions are released from the channels of the sarcoplasmic reticulum, their concentration increases;
- calcium ions increase the ATPase activity of myosin;
- globular G-actin transforms into fibrillar (F-actin), capable of interacting with myosin in the presence of ATP decay energy;
- ATP decay energy initiates the interaction of myosin with fibrillar actin with the formation of an actomyosin complex.
The result of the reduction is an increase in meat stiffness, a decrease in elasticity and a decrease in the level of water-binding capacity.
A decrease in protein hydration affects meat stiffness as the pH of muscle tissue approaches the pH of the isoelectric point of the major proteins. The greatest rigidity of meat is observed at pH = 5.5. When mixing the pH in any direction from the isoelectric point of the proteins, the tenderness of the meat increases. The shift in pH leads to wedging of the polypeptide chains of individual proteins, an increase in hydrophilic centers and, accordingly, an increase in the moisture absorption capacity of meat. [5]
In recent years, much attention has been paid to the use of lactic acid and its salts in the development of a wide range of meat products to give them various consumer properties, including increasing the shelf life of products and increasing their shelf life. However, the information available is mainly devoted to the study of effects on cooked products. In this regard, the study of the mechanism of action and the possibility of a purposeful change in the processes occurring during the processing of meat raw materials with lactic acid salts will reveal their potential properties and the ability to maintain the quality of meat products.
Previously, it was shown that the treatment of fresh meat with brine containing 100 mmol CaCl2 accelerates the degradation of cytoskeletal proteins responsible for tenderness of meat, and thus promotes faster tenderization of muscle tissue (in three days).
The aim of this work was to study the structural changes in muscle tissue and its proteins under the influence of various concentrations of calcium lactate.
The object of research is the longissimus dorsi muscle of beef of the I fatness category with a pH of 5.74. After 1-1.5 hours from the moment of slaughter of the animal, fresh meat was subjected to trimming with the separation of visible adipose and connective tissue.
Figure 1. Dependence of pH on concentration: 1 - calcium lactate; 2 - calcium chloride (1 day)
Figure 2. Dependence of pH on concentration: 1 - calcium lactate; 2 - calcium chloride (2 days)
For the experiments, samples of muscle tissue weighing 500 g were taken, which were injected with the appropriate brines in an amount of 15% of the meat weight. Samples of muscle tissue treated with 10% brine in the absence or presence of calcium lactate were studied in the concentration range from 4 to 100 mmol. Samples treated in this way were stored at 4 ± 2°C for 120 hours. Every 24 hours, samples were taken from each sample for research using microstructural analysis and differential scanning microcalorimetry.
Results&discussion
As a result of the studies of the microstructure of the muscle tissue of control and experimental samples, it was found that with an increase in the concentration of exogenous calcium, the severity of destructive processes increased.
The greatest depth of destruction of muscle tissue was noted when calcium ions were used at a concentration of 100 mmol. Already after 72 h of storage, multiple microcracks were observed in muscle fibers, and by 96 h, homogenization, loosening of myofibrils in muscle fibers, and their multiple disintegration along Z-plates were observed. When meat ripened under such conditions, by 120 h of incubation, destructive processes took on a widespread character, covering the bulk of the muscle fibers in the sample, while in control samples, the violation of the integrity of muscle fibers by 120 h of storage was of a local nature. It should be noted that the treatment of muscle tissue with brines containing calcium lactate led to a disruption in the structure of Z-lines serving as the supporting apparatus of sarcomeres, their homogenization and destruction. The noted changes ultimately underlay the violation of the integrity of the fibers and led to an acceleration of the autolysis process and an increase in the tenderness of the meat compared to the control samples.
The thermodynamic characteristics of muscle proteins were studied using a modern method - differential scanning microcalorimetry. The most informative parameter describing the structural and temperature-denaturation stability of muscle tissue proteins is the dependence of the temperature of the middle of denaturation transitions on the storage time of salted samples. Previously, it was shown that calcium ions act primarily on myofibrillar structures and induce the destruction of cytoskeletal proteins. The first denaturation transition most likely reflects changes in the structural and denaturation stability of cytoskeletal matrix proteins. The second transition is mainly due to changes in the structural and denaturation stability of proteins of the actomyosin complex. According to the same authors, the third transition can be attributed to thermal denaturation of connective tissue proteins and coagulation of muscle proteins.
Conclusion
Temperature changes in the middle of irreversible denaturation transitions were investigated for samples treated with brine containing different concentrations of calcium lactate for 120 hours. Temperatures were calculated from Gaussian curves describing each irreversible transition. This parameter reflects a change in the structural stability of muscle tissue proteins.
During storage of meat samples treated with 10% brine without calcium lactate (control), a gradual decrease in the temperature of the first denaturation transition from 58°C at 24 h of salting to 55°C after 120 h of salting was revealed. This indicates a gradual decrease in the thermal stability and structural stability of myofibrillar proteins during the autolysis of salted meat. Changes in the temperatures of the second and third denaturation transitions in these samples were not detected even after 120 h of storage.
Treatment of raw meat with brine containing 4 mmol of calcium lactate leads to a similar decrease in the temperature of the first denaturation transition, as in the control. At the same time, in the presence of 4 mmol of calcium lactate, a decrease in the temperature of the second denaturation transition from 69.5 to 65 °C is found. This may indicate a destructive effect of such a concentration of calcium ions on the proteins of the actomyosin complex. The third denaturation component in this case does not change.
The most significant changes in thermodynamic characteristics in the case of treatment of muscle tissue with 10% saline in the presence of 100 mmol of calcium lactate. The temperature of the first denaturation transition decreases from 60.6°C after 24 hours of storage to 55.5°C after 120 s. The change in the temperature of the second denaturation transition is of the same nature (69°C at 24 h, 64°C at 120 h of curing). The temperature of the third transition, reflecting the thermal denaturation of connective tissue proteins and the transition of all muscle proteins to a coagulated state, also decreases from 77 °C (24 hours of salting) to 72 °C (120 hours of salting).
Thus, by the method of microstructural analysis, it was found that the greatest depth of destruction of muscle tissue is observed when using a 10% brine containing 100 mmol of calcium lactate, introduced into the raw material in an amount of 15% of the initial mass. By 96 hours of storage, multiple microcracks, homogenization, loosening of myofibrils and their multiple disintegration along Z-plates are found in muscle fibers.
Microcalorimetric studies of muscle tissue showed that the structural stability and thermal stability of muscle tissue proteins treated with 10% brine containing 100 mmol of calcium lactate are significantly weakened compared to control samples.
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