EFFECT OF COW S MILK TREATMENT WITH TRANSGLUTAMINASE ON THE COMPOSITION AND QUALITY OF YOGHURT WITH PARTICULAR REFERENCE TO ITS BIOLOGICAL VALUE

The aim of this study was to evaluate the impact of cow s milk treatment with transglutaminase (TGase) enzyme on the resultant yoghurt attributes with emphasis on the biological properties. Yoghurt was made using milk treated previously with TGase at levels of nil (the control), 250 and 500 units/1 yoghurt milk at 40°C for 2 h. Then, the enzyme was inactivated by heating, inoculated with 2% of freshly activated yoghurt starter culture (YSC), and incubated until complete coagulation. The obtained results indicate that the TGase treatment of yoghurt milk led to significant increments In the contents of dry matter (DM), protein/ OM, lactose/OM, ash/OM, Ca, P, K, Mg, Cu and Zn, the amino acid (AA) threonine and all non essential (E) AA, except of histidine, true digestibility %, biological value % and net protein utilization %.On the contrary, the fat/DM content, Fe, Mn, vitamin B2, glutamic acid and EAA lysine, methionine, cystine, leucine, isoleucine, phenylalanine, tyrosine and valine decreased, while those of Na, vitamin B1 and the growth rate of rats fed on TGase treated yoghUrts were not changed. The growth of both strains of YSC slowed significantly down as TGase level was raised. TGase treatment of yoghurt milk led to obtain a yoghurt body with higher values of consistency coefficient and yield stress versus the control. The blood picture of rats fed on TGase treated yoghurts did not exhibit any significant differences either in the hemoglobin value or hematocrit %. While the red blood cell and the white blood cell counts were significantly higher in the blood of tats fed on TGase treated sample. The change rates in most attributes became more pronounced as tGase dose was progressed. Rats feeding on TGase treated yoghurt was associated with significant Increment in the total as well as globulin protein and In levels of Cn, K, Mg, Cu, Fe and Zn in their blood plasma. On the contrary, the ratio between them appeared Proportional decrement related to the enzyme dose. The feeding on yoghurt led to reduce In the E. coli count of rats feces and to obvious predominance of the yoghurt starter strains. From the foregoing results it can be conclude that, TGase treatment of yoghurt milk gave a product of better consistency and improved the protein and mineral bioavailability and blood and blood plasma pictures of experimental animals.