Influence of Shear Stirring and Homogenization on Serum Separation of Doogh

During storage, serum separation is a major defect that affects the market share of Doogh. Therefore, in the present study the effects of high shear stirring and homogenization, as major operation units, on the stability was investigated. To do so, Dooghs were stirred at various speeds and time scales (9000 rpm and 11000 rpm for 30 s and 2 min), homogenized at different pressures (0, 20, 50, 80, 100, 120, 150, 180 and 200 bar), as well as treated at combined conditions of agitation and homogenization (9000 rpm, 1 min; 11000 rpm, 1 min; 100 and 200 bar) and their effects on serum separation of Iranian Doogh (59.3% water, 0.7% salt and 40% yoghurt) were studied. Our results revealed that shear stirring and homogenization could significantly increase serum separation in comparison with control where the effect of stirring speed was more pronounced (P<0.01). Moreover, the influence of their combination was considerablely higher than their effects in a single form. In addition, following all these treatments the apparent viscosity reduced and a significant increase in serum separation perceived.