Effects Of Microbial Transglutaminase Induced Protein Cross-linking Of Porcine Leg Myofibrillar And Pork Batter Gel Properties

The myofibrillar proteins are involved in producing the different functionalities in processed muscle foods. Texture, moisture retention and tenderness of processed muscle foods are influenced by the functionality of this protein. It plays a significant role in causing product variations among different muscle types and species based on the pH. Naturally occurring covalent crosslinks play an important role in the structure-function relationships of proteins. The functional properties of food proteins may be modified by altering the natural crosslinks or by introducing new crosslinks into the protein structure by enzyme microbial transglutaminase (MTGase) through formation of covalent cross-links.The effect of protein concentration and pH on protein solubility, gel strength, cooking loss and heat-induced gelation properties of porcine leg myofibrils was investigated. Myofibrils suspended in 0.6 N NaCl, pH 6.0 showed increasing gel strength and gelling properties with increasing protein concentration. However, increasing protein concentration had a negative effect on protein solubility and positive effect on cooking loss. In addition, leg myofibrils showed increasing protein solubility with storage at 4°C. Results indicate protein solubility, gel strength, cooking loss and dynamic viscoelastic properties of porcine leg myofibrils are pH dependents. Highest gel strength (44 g·cm) was noted in pH 6.0, while highest protein solubility (60 %), highest water holding capacity [(WHC), 87 %] and lowest cooking loss (50 %) in pH 7.0. Poly acrylamide gel electrophoresis (SDS-PAGE) was conducted to investigate the success of extraction, effect of pH on solubility of different protein and effect of temperature on denaturation of major proteins present in porcine leg myofibrillar. SDS-PAGE revealed that extaction contains all proteins with compare to the published data. However, based on the intensity of the bands it confirmed that major proteins present in myofibrillar are myosin (~ 200 kDa) and actin (~ 43 kDa). No major changes in protein bands were observed in an extraction pH range from 6 to 7.5. But low solubility of myosin and actin was noted at pH 5.5. Further, it was noted that denaturation of myosin and actin proteins at temperature above 50°C.The effects of processing conditions i.e., different heating methods (conduction, convection and radiation), ionic strength (zero, 0.2, 0.4 and 0.6 N NaCl), MTGase/protein concentration, pH (5.5, 6.5, 7.0 and 7.5), combined effect of (sodium caseinate) non muscle/muscle, high pressure (200 and 400 MPa) and heating temperature (20 to 90°C) on MTGase induced pork myofibrillar protein were observed through the SDS-PAGE pattern. The high intensity of myosin band in control samples indicates no interactions or even low non-disulfide covalent protein interactions. Regardless the processing conditions, the intensity of myosin band were reduced gradually using 5 and 2.5 g kg-1 MTGase. The decrease in intensity indicates increasing myosin aggregation during the over night incubation. The formation of the giant polymers (high intensity at the top of the gel) was only visible during incubation. The myosin and actin exhibited major changes and were cross-linked during incubation at 4°C. In addition, increase in intensity of myosin and actin bands indicates more extraction of those proteins when increasing protein concentration and ionic strength. The results indicate that MTGase effectively induced cross-link formation at pH range 5.5–7.5. Electrophoretic analysis of the sodium caseinate alone exhibited major changes and subunits (βandα) was cross-linked with MTGase. Hence, MTGase catalysis of myofibrillar/sodium caseinate cross-linking or intramolecular association was independent of the preponderance of the one group of...