COMPARISON OF TECHNIQUES FOR MEASURING THE RHEOLOGICAL PROPERTIES OF LABNEH (CONCENTRATED YOGURT)

The effectiveness of conventional rheological techniques (destructive) and the oscillatory dynamic test (non-destructive) for the study of t he physical properties of concentrated yogurt (labneh) was studied Six different types of labneh (control (cloth bag method), ultrafiltrated (UF)-after and -before fermentation, reverse osmosis (RO)-after and - before fermentation and direct reconstitution from whole milk powder) were examined. Dynamic rheological studies revealed that labneh is a v iscoelastic system in which its elastic characteristic is more dominan t than its viscous properties. The elastic and viscous attributes of t he control labneh were significantly different from the rest of the te st samples. In general, the samples with low protein content (RO-after and -before fermentation and direct reconstitution labneh) produced w eaker gel structures than their UF counterparts. The penetrometer and viscometer (destructive techniques) failed to reveal expected differen ces between the samples, and the results did not correlate with the os cillatory dynamic tests. In the light of these results, it could be su ggested that dynamic studies are much more reliable than the destructi ve rheological techniques for the study of the physical properties of labneh.