Influence of ultrafiltered milk permeate and zedo gum on qualitative properties of doogh

The effect of zedo gum (with concentrations of 0, 0. 2 and 0. 4 %) on qualitative properties of doogh made from yoghurt diluted by UF milk permeate (at levels of 0, 25 and 50 %) as replacement of water was studied during storage for one month at 4ºC using response surface methodology and face centered design. The results showed that serum separation decreased with increasing the levels of permeate and zedo gum and it increased during storage (p<0. 05). Apparent viscosity also increased with increasing the levels of permeate and zedo gum, but it's changes during storage was not significant (p>0. 05). Acidity was considerably affected by permeate, zedo gum content and storage time. Both permeate and zedo gum resulted in lower moisture content, for increasing the dry matter and absorbing water, respectively. Density was increased only by permeate. According to the results obtained from color analysis, L* value increased during storage time but it decreased under the interaction of permeate and zedo gum. At lower levels of zedo gum, the increase of permeate caused a lower a* value. However higher levels of zedo gum resulted in a higher a* value. Both permeate and zedo gum resulted in b* value improvement. The results of sensory analysiاs showed that permeate caused the score of flavor decrease and zedo gum caused the score of consistency increase during storage. The amounts of 0. 19% zedo gum, 32. 55% permeate and 30 days storage were obtained as optimum conditions.