Gelation Properties of Swine Plasma

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Gelation of swine plasma with 4% protein concentration was observed when heated at 70oC. Gel strength of those gels increased with the increasing heating temperature (70-95oC), heating time (0-60min) and protein level (4.3-7.2%), while decreased with the increasing level of NaCl (0-3%). The optimal pH for gel strength was 10. Except heating, gelation of plasma also could be induced by the addition of thrombin and calcium ion, and by dialysis to remove the anti-coagulant (Na-citrate) at ambient temperature. Addition of various levels (2.7-11.7U/mL plasma) of thrombin did not influence the gel strength of thrombin-induced gel after thermal treatment at 80oC for 20 min. Addition (500-2200ppm) of calcium to plasma enhanced the gel strength of thermally treated gels. However, the calcium-induced gelation was apparently inhibited by the addition of heparin to plasma. Compared with the gel strength (33g x cm) of 80% plasma heat-induced gel (80oC, 20min), addition (2.7U/mL) of thrombin, low level (500-800ppm) of calcium and high level (2200ppm) of calcium increased the gel strength by 4-5 times, 14-15 times and 45 times, respectively. Gel strength of thermally treated dialysis-induced gel approximated to low level (500-800ppm) of thermally treated calcium-induced gel. Besides, optimal effect of calcium bridges on increasing the gel strength (by 70%) of heated gel was at the level of 500ppm calcium in plasma. The first derivative of the time-dependent turbidity change of 80% plasma added with various level of calcium present the maximal slope (Vm) of absorbance change which revealed the rate of blood-clotting. The period of time (TVm) to Vm indicated the time required for the activation of blood-clotting enzymes. In 80% plasma (containing 0.4% Na-citrate) two peaks (Max. Vm1 at 1200ppm calcium and Max Vm2 at 1500ppm calcium) and one valley (Min. Vm at 1350ppm calcium) were observed in the Vm curve, while only one valley (Min. Tvm at 1200ppm calcium) was in TVm curve. Those results revealed two types (Max. Vm1 and Max. Vm2) of gelation mechanisms were involved in the plasma clotting in the presence of calcium. Max. Vm2 was more contributory to the gel strength. Furthermore, linear relationships of Max. Vm1, Max. Vm2 and Min. TVm between calcium content and 1/protein concentration were observed. The major characteristic of unheated gels prepared by the addition of thrombin or calcium, or by dialysis to remove anti-coagulant was the lack of cohesiveness, compared with that of the heated gels. However, thermal treatment enhanced the rigidity, gel strength, gumminess and chewiness of plasma gels. The properties of thrombin-induced gel did not varied with the level of thrombin if the level of it was higher than 2.7U/mL plasma. However, some properties of calcium-induced gels, such as rigidity, gel strength and gumminess, increased with the increasing calcium content (500-2200ppm) in the 80% plasma. Clottability and recovery of fibrinogen from plasma by cold (4oC) precipitation method was 54% and 350-400mg/dL plasma, respectively. While those of fibrinogen from plasma by isoelectric point method was 76% and 300mg/dL plasma, respectively. However, isoelectric point method was liable to cause fibrinogen denaturation. Through separation of Sephacryl S-300 HR filtration chromatography, clottability of fibrinogen prepared by the former method and the latter method was increased to 96-99% and 92-96%, respectively. Results from SDS-PAGE also revealed the high purity of fibrinogen prepared. Addition of calcium caused the gelation of crude fibrinogen (prepared by 4oC cold precipitation), similar to that of plasma, revealed the existence of blood blotting-enzymes in the crude fibrinogen. Mixture of crude fibrinogen (0.75 % protein) and egg white or soy protein isolate (5.0 % protein) could cause gelation in the presence of 500ppm calcium. Gel strength of heated fibrinogen mixed with egg white gels (80oC, 20min) was almost the same to that of plasma gel but higher than that mixed with soy protein isolate.