A potential method for determining in situ gelatinization temperature of starch using initial water transfer rate in whole cereals

Abstract

Twelve whole cereal grains (3 soft wheats, 3 hard wheats, 3 dent corns, and 3 rices) were soaked in distilled water at different temperatures ( T) between 35 and 95 °C for a short period of time ( t soak). In all grains, initial water transfer rate ( R) linearly increased with increasing T and abruptly assumed a steeper slope at some T ( T bre). Gelatinization temperature ( T gel) of the ground samples of the same grains were determined using differential scanning calorimetry (DSC). T bre values were always close to and higher than T gel values obtained from DSC ( T DSC). Polarized light microscopy (PLM) showed that gelatinization did not take place in the outermost zone of the endosperm of whole grains below T bre, however it did above T bre. Depending on T DSC can be taken as the in vitro T gel and findings of this and previous works, T bre from the R–T plots (break-point method) was assessed as the in situ T gel. The principle of the break-point method depends on abruptly changing initial water transfer rate in whole grains upon gelatinization in the outermost zone of the endosperm. In addition to some advantages over the recognized methods invasively determining in vitro T gel, the break-point method is for determining in situ T gel of intact starch in whole grains noninvasively.