Effect of transglutaminase on heat-induced gel properties at acid pH of mixtures of plasma and haemoglobin hydrolysates from porcine blood

摘要

The purpose of the present study was to determine the effects of treating protein solutions prepared by mixing different percentages of haemoglobin hydrolysate (HbH) and plasma from porcine blood with microbial transglutaminase (MTGase) on the properties of thermal-induced gels at pH 5.5. Spray-dried plasma and freeze-dried HbH, obtained through enzymatic hydrolysis of haemoglobin concentrates by trypsin and pepsin, were used to prepare 7% (w/v) protein solutions. Two HbH:plasma ratios (expressed in a protein content base) were tested: 0.25%:6.75% and 0.75%:6.25%, respectively. Solutions were adjusted to pH 7.0 just before their incubation at 30 °C for 3 h with different MTGase concentrations (1, 3 and 5% of the commercial enzymatic product). After the enzymatic treatment, solutions were lowered to pH 5.5 and submitted to the thermal gelation process (80 °C for 45 min). Texture (hardness, springiness and cohesiveness from TPA curve) and water holding capacity (WHC), determined as water released after centrifugation, were the evaluated gel properties. Cross-linking at some of the tested conditions was determined using SDS-PAGE electrophoresis. The results indicated an overall better gelling ability of the lowest HbH-content mixtures relative to those containing the highest HbH-content ones, with a clearly different behaviour regarding the MTGase effects. At the lowest HbH percentage, the treatment with MTGase had no effects on the gel properties regardless of the enzyme concentration and obtaining, moreover, very similar values relative to those of gels from untreated solutions. By contrast, at the highest HbH percentage, gel hardness tended to diminish as MTGase concentration increased, at any case too softer to determine the WHC. SDS-PAGE profiles showed a decrease in the formation of high molecular weight polymers as the percentage of HbH increased, suggesting that its presence hindered the enzyme cross-linking activity.