A 2-factor-5-level central composite rotatable design (CCRD) of response surface methodology (RSM) was used to model linear, interaction and quadratic effects of some processing variables (salep and each starch type, the composition variables) on the response variables; physicochemical characteristics (pH, brix and turbidity) and steady shear rheological properties (apparent viscosity h, consistency coefficient K, shear stress sigma and flow-behavior index n) of salep-starch mixtures (SSM); namely, salep-corn starch mixture (SCSM), salep-wheat starch mixture (SWSM) and salep-potato starch mixture (SPSM). The linear, interaction and quadratic effects of the processing variables were also modeled to develop predictive models for the tested properties to optimize the effect of these variables (salep and each starch type) using ridge analysis involved with RSM. It was concluded that salep and all starch types increased the apparent viscosity (eta), shear stress (sigma) and consistency coefficient (K) values; decreased the flow-behavior index (n) values of SSM samples. Salep was observed to vastly increase the viscosity of mixture samples when mixed with corn, wheat or potato starches. However, potato starch exhibited very different performance as compared to the other starches in terms of the physicochemical and steady shear rheological properties. The ridge analysis used to optimize these effects revealed that maximum h (0.84, 0.46 and 1.38 Pa s), and K (16.64, 6.48 and 28.86 Pa s(n)) values for the SCSM, SWSM and SPSM samples, respectively would occur at salep 0.54% and starch 2.83% w/w. (C) 2012 Elsevier Ltd. All rights reserved.