This paper shows that acidic conditions provide substantially higher % acetyl content, intrinsic viscosity and thermoplasticity even at low ratios of acetic anhydride and catalyst concentrations compared to using alkaline conditions for acetylation of oil-and-zein-free distillers dried grains with solubles (DOGS). Conventional methods of carbohydrate and protein acetylation are unsuitable for acetylating DDGS which is a mixture of carbohydrates and proteins. In this research, methods were developed to simultaneously acetylate the carbohydrates and proteins in DDGS using alkaline and acidic catalyses. The effect of various acetylation conditions on the % acetyl content and intrinsic viscosity of DOGS acetates was studied. Acetylation of DOGS was confirmed using FTIR and H-1 NMR and thermal behavior of the DOGS acetates was studied using TGA and DSC. The highest % acetyl content obtained was 28.1% (Degree of substitution (DS) of 1.5) under alkaline conditions using an anhydride to DDGS ratio of 3:1 whereas a much higher % acetyl content of 36.1% (DS 2.1) was obtained under acidic conditions even with a lower anhydride to DDGS ratio of 2:1. DDGS acetates obtained using alkaline catalysts also had higher melting temperature and low melting enthalpy and hence exhibit poor thermoplasticity compared to the DDGS acetates obtained using acid catalysts. (C) 2010 Elsevier Ltd. All rights reserved.