Background: Microbial proteases are the most important enzymes in the industry, accounting for 60% of total enzyme sales in the world. The proteases of lactic acid bacteria (LAB) have received special attention because of their importance in the food and dairy industry.
Methods: The crude extract and purified protease enzyme produced from an isolated bacte- rial strain identified as Lactobacillus plantarum were used in the ripening and flavor improvement of soft white cheese (Domiati-type). The effect of protease enzyme on the chemical and sensory properties of Domiati cheese during the storage period was studied.
Results: The results showed that the pH value, moisture and protein contents of all Domiati cheese treatments decreased by adding protease and increasing the storage period, whereas the soluble nitrogen, tyrosine and tryptophan and fat contents for all cheese treatments increased with protease addition as the storage period advanced compared to control. Moreover, most free fatty acids (FFA) contents were similar between the control and protease cheese treatments during the storage period, whereas free amino acid (FAA) content increased as the storage period for protease cheese treatments was increased. The predominated free fatty acids in Domiati cheese at the end of the ripening were palmitic acid, followed by oleic acid, stearic and myristic acids. Free amino acids (glutamic acid, proline, leucine, aspartic, lysine, serine and valine) were present in higher concentrations and represented more than 50% of total amino acids in all Domiati cheese samples at the end of the ripening period. The results of sensory evaluation indicated that as the ripening period progressed, the flavor characteristics gradually increased, leading to an improvement in the organoleptic properties compared with the control. The results showed that at end of the storage period, the cheese treatment (T2) with 2% crude enzyme recorded the highest flavor score.
Conclusions: It be concluded that the addition of 2% of crude protease enzyme accelerates the ripening process of Domiati cheese through 60 days without any defects.  .
Keywords: Domiati cheese; free amino acid; free fatty acid; protease; ripening process; sensory evaluation.