Response surface methodology was used to study the effects of locust bean gum (LBG), dry matter concentrations and storage time on the physical properties of low-fat set yoghurt. Low-fat yoghurt samples were manufactured using two different methods. In these samples, the polysaccharide concentrations were 0.002, 0.02 and 0.038 g 100 g(-1), and dry matter concentrations were 10, 12 and 14 g 100 g(-1). Viscosity, water holding capacity (WHC), syneresis, pH and acidity analyses were applied to the samples after 1, 7 and 14 days of storage at 4degreesC. Analysis of variance (F-test) showed that a second-order equation model is well adjusted to predict the experimental data. Lack-of-fit tests did not result in a significant F-value. Determination coefficients (R-2) were greater than 76%. In both processing methods, viscosity and WHC in the samples increased with increasing levels of dry solids although syneresis decreased. WHC and viscosity decreased when the LBG concentration was above 0.02 g 100 g(-1), whereas syneresis increased. The ideal concentrations of dry matter and LBG were found to be 14 and 0.02 g 100 g(-1), respectively. (C) 2003 Published by Elsevier Ltd.