Enzymatic Modification to Stabilize the Fermented Milk Drink, Doogh

In this study, the effect of enzyme transglutaminase on physicochemical and sensory characteristics of the fermented milk drink, Doogh, was investigated. Also, the influence of two preparation methods, i.e., water addition to yoghurt as a common method and fermentation of diluted milk as an alternative, was studied. The enzyme was applied into the skim milk either before or after pasteurization followed by thermal inactivation. Doogh prepared by fermentation of diluted milk resulted in more stable products with less phase separation. Enzymatic treatment after pasteurization of milk followed by water addition and fermentation yielded the least phase separation during storage. Doogh stability was associated with improvement of other physicochemical properties of the product such as increase in the apparent viscosity, storage modulus and uniformity of particles accompanied by whiter appearance and finer meshed network and smaller pores in their microscopic structure. Enzymatic treatment resulted in lower sensory scores evaluated by panelists. Practical Applications Fermented milk drinks, including the Iranian Doogh, are healthy and refreshing beverages. Serum separation is the main textural defect in these types of products. Transglutaminase, a cross‐linking enzyme, can be used to improve the physicochemical characteristics of Doogh. Application of transglutaminase after pasteurization in water‐added milk as an alteration in industrial processing causes more stable product, less energy consumption especially at the cooling step and faster preparation. In Doogh manufacturing, transglutaminase must be inactive to prevent forming protein clots during storage; therefore, transglutaminase cannot be added simultaneously with starter culture in this case.