Mechanism Of Crude Extract From Alaska Pollock And Beef Muscle In Tenderizing

Consumer acceptance of meat is strongly influenced by the eating quality including tenderness, juiciness and flavor. Tenderness is mainly determined by the structure and characteristic of myofibrillar and intramuscular connective tissue. The commercial meat tenderizer destroyed the structure of myofibril, while it has a tendency to over-tenderize the meat surface, leading to undesirable "mushy" meat, and also off-flavor was hardly to accept. In this study, we researched on the degradation of myofibrils and perimysia from beef muscle incubated with the crude extracts from Alaska pollock and beef muscle, utilizing by SDS-PAGE gel electrophoresis, circular dichroism, raman spectroscopy, scanning electron microscopy technique, also the changes of secondary structure and microstructures of proteins during the incubation were investigated. The objectives of this work were to discuss that the potential the crude extracts from Alaska pollock and beef muscle for tenderizing meat in order to provide a new way for beef tenderizing and a theoretical basis for the actual production. The detailed contents and results are shown as follows.The activity of cathepsin B and L in crude extracts from Alaska Pollock and beef muscle was determined. According to SDS-PAGE, it was found that the crude extracts from Alaska Pollock and beef muscle were protein mixture, of which molecular weight was lower than55kDa. It was consistent with the researches on the molecular weight of cathepsin B and L. The crude extracts of Alaska Pollock and beef muscle could hydrolyze the specific fluorescent synthetic peptide substrate z-Arg-Arg-MCA of cathepsin B and the specific fluorescent synthetic peptide substrate z-Phe-Arg-MCA of cathepsin L. The activity of cathepsin B in Alaska Pollock and beef muscle were21.86U and19.10U, the activity of cathepsin L in Alaska Pollock and beef muscle were22.36U and20.72U. The optimum temperature of cathepsin B from Alaska Pollock and beef muscle hydrolyzed its specific fluorescent synthetic peptide substrate z-Arg-Arg-MCA was50℃and40℃, the optimum pH was5.0and5.5, respectively. And the optimum temperature of cathepsin L from Alaska Pollock and beef muscle hydrolyzed its specific fluorescent synthetic peptide substrate z-Phe-Arg-MCA was50℃C and40℃, the optimum pH was5.0and5.5. DTT played a role in activation to cathepsin B, and the activator of cathepsin L was L-Cys. Low concentrations of E-64inhibited the activity of cathepsin B and L.Crude extracts from Alaska Pollock and beef muscle hydrolyzed myofibrill proteins and the secondary structure of beef myofibrillar proteins changed. The effect of crude extracts from Alaska Pollock and beef muscle on the hydrolysis of beef myofibrillar protein and the changes of secondary structure were estimated by SDS-PAGE and CD. It was found that myosin in beef myofibrillar protein was completely hydrolyzed after12h of incubation, troponin T and tropomyosin were degraded entirely after24h of incubation with the crude extracts from Alaska Pollock muscle. Whereas, only myosin in beef myofibrillar protein was completely hydrolyzed after24h of incubation with crude extracts from beef muscle, actin was partially degraded with both crude extracts. The content of a-helix in beef myofibrillar protein was reduced after treating with the crude extracts from Alaska Pollock and beef muscle, achieving to7.51%and17.53%, and content of β-sheet increased to42.82%and33.53%, respectively. According to TEM and SDS-PAGE, beef tenderness was significantly increased, as the myofibrillar proteins hydrolyzed. Myosin thick filament was damaged firstly, and then the actin thin filament was destroyed, while the structure of Z-band was not damaged after incubating with cathepsin B and L in Alaska Pollock and beef muscle. Maybe there was no effect of cathepsin B and L in Alaska Pollock and beef muscle on the cytoskeletal proteins.Crude extracts from Alaska Pollock and beef muscle hydrolyzed perimysium proteins and the secondary structure of collagen changed. It was investigated that perimysium from beef muscle was hydrolyzed with concentrations of the crude extracts from Alaska Pollock and beef muscle for different hours. The collagen was dissolved, the secondary structure in collagen and intensity of proline and hydroxyproline changed, meanwhile the microstructure of perimysium was determined with SEM. The content of collagen dissolved from perimysium was increased gradually, as the concentration of crude extracts from Alaska Pollock and beef muscle and incubation time increasing, the maximum were34.81%and15.93%. The content of α-helix was the lowest, and the content of β-sheet was the highest after6h of incubation. The content of α-helix and β-sheet in perimysium incudated with crude extracts from Alaska Pollock muscle for6h were8.26%and55.44%; while the contents of α-helix and β-sheet in perimysium incudated with crude extracts from beef muscle for6h were18.58%and47.53%. According to SEM, the collagen fibrils were destroyed with the incubation of crude extracts from Alaska Pollock and beef muscle. The collagen fibers partly splited to collagen macrofibrils, dispersed collagen microfibrils gradually formed, and then associated with the dissolved collagen. The hydrolytic destruction of perimysum indicated the tederiztion of beef muscle.The mechanism of crude extract from Alaska Pollock and beef muscle in tenderizing was that the cathepsin B and L in crude extract from Alaska Pollock and beef muscle well hydrolyzed myofibril and perimysium. Myosin and actin degraded, while the structure of Z band was not affected. Meanwhile, collagen fibers destroyed into collagen macrofibers and collagen microfibers, and collagen gel formed. Then beef muscle was well tenderized.Beef was tenderized with the crude extracts from Alaska Pollock and beef muscle, meanwhile the flavor and juiciness were held. The effect of crude extracts from Alaska Pollock and beef muscle on beef tenderness was determined. The shear force value of beef incubated with crude extracts from Alaska Pollock and beef muscle reduced by30%and48%, the tenderness significantly increased. Meanwile, there was no effect of crude extracts on beef flavor, color and juiciness. It was conclude that crude extracts from Alaska Pollock and beef muscle could be utilized as a potential meat tenderizer, and there was a broad application prospects.