High-methoxy pectin (HMP), propylene glycol alginate (PGA), carboxymethyl cellulose (CMC) and xanthan gum (XG) were added separately to whey fermented by a yoghurt starter culture at concentrations that yielded a viscosity similar to that of commercial fermented milk beverages. Mouthfeel and flavour of the samples were assessed by a highly trained panel, and volatile analysis was performed by proton-transfer reaction mass spectrometry to determine the effect of hydrocolloids on the partition of flavour compounds in the headspace. CMC and HMP produced significantly higher thickness than PGA and XG; PGA caused a 'gritty' mouthfeel. The yoghurt aroma of the samples containing CMC and PGA was perceived as less intense compared with the control, consistent with a reduced concentration of key volatile compounds in the headspace of these samples. (c) 2006 Elsevier Ltd. All rights reserved..