In this study, the effects of gamma irradiation on the rheological characteristics of guar gum, pectin and salep were investigated. Hydrocolloids were irradiated at 0, 2.0, 4.0, 6.0, 8.0 and 10.0 kGy. Although the increasing irradiation dose generally caused a decrease in apparent viscosity (AV) of hydrocolloid solutions, the magnitude of the effect of the irradiation on the AV was different for different hydrocolloids. The irradiation affected the consistency index (CI) of each hydrocolloid analyzed differently. The Cl of guar gum was very sensitive to irradiation treatment and it was 1989 mPa s(n) for control sample and decreased to 35 mPa s(n) after 10 kGy of irradiation. On the other hand, the change in the Cl of salep and pectin solutions with irradiation was not drastic as it was observed for guar gum solution. The CI of salep and pectin were initially 24.83 and 24.24 mPa s(n) and decreased to 20.01 and 16.98 mPa s(n) after irradiation, respectively. The flow behavior indexes of hydrocolloid samples studied were significantly (p < 0.05) affected from the irradiation dose. It can be concluded from the results of the study that guar gum was not appropriate for preservation by irradiation considering the fact that its CI and AV decreased when the samples were irradiated. On the other hand, the rheological properties of pectin and salep were not considerably affected from irradiation; hence, they can be irradiated for preservation purposes. (c) 2006 Elsevier Ltd. All rights reserved.