The effect of hydrophobic modifications on the adsorption isotherms of cassava starch

Moisture sorption isotherms of native and ten hydrophobically modified cassava starches were determined at 25 degrees C using a moisture sorption analyzer in an a(w) range of 0-0.94. Modified cassava derivates were obtained by modifying native cassava starch (CS) with octenyl succinic anhydride (OSA) and by modifying a carboxymethylated cassava starch (CMCS) with quaternary ammonium salts having different alkyl chain lengths (C-n TAB with n = 12, 14, 16, and 18). In comparison to native cassava starch, the results obtained showed that OSA modification yielded a more hydrophobic material for the whole a(w) range, while the ionic complexes obtained from CMCS and quaternary ammonium salts produced more hydrophobic starches at low a(w) values and more hydrophilic ones at high a(w) values. It was found that the experimental data were well represented by the GAB model and that the monolayer water contents decreased with chemical modification. The moisture sorption kinetic parameters showed that water adsorption process became slower in chemically modified starches. (C) 2010 Elsevier Ltd. All rights reserved.