Preparation, pasting properties and freeze-thaw stability of dual modified crosslink-phosphorylated rice starch

The pasting properties and freeze-thaw stability of one step combined modifications of rice starch through crosslinking and phosphorylation reactions were studied and compared to those modified by crosslinking or by phosphorylation alone. The native rice starch was mixed with a solution of pH 9.5, containing 1% sodium trimetaphosphate (STMP) and 4% sodium tripolyphosphate (STPP). The starch mixture with approximately 27% moisture content was granulated and heated in a hot air oven at 120 degrees C allowing the gradual evaporation of water to dryness up to 2 h reaction time. The combined modifications provided higher peak, breakdown, final and setback viscosities than that of the phosphorylation alone. However, these pasting properties of both combined modifications and phosphorylation were increased in line with the increase of reaction time. In contrast to that of the crosslinking reaction with 1% STMP which provided the decreasing of those pasting properties with the increase of reaction time. The pasting temperature for both the combined modifications and phosphorylation were decreased in line with the reaction time, while those for the crosslinked starch were increased. The freeze-thaw stability of native and modified rice starch pastes for five cycles were studied. The combined modified rice starch provided the highest freeze-thaw stability, and this type of modified rice starch could be used to prepare food products with good freeze-thaw stability. (C) 2007 Elsevier Ltd. All rights reserved.