Effect of storage proteins on pasting properties and microstructure of Thai rice

This study investigated the influences of rice storage proteins, in relation to amylose content, on pasting properties of newly harvested Thai rice. The polished rice cultivars investigated included waxy rice SPT1, which contained 1.3% amylose and 8.3% protein; and non-waxy rice, namely PTT1 and LPT123, which contained 14.1% and 28.6% amylose, and 6.7% and 9.6% protein, respectively. The characteristics of protein fractions were altered by accelerated aging at 60 °C and 70% relative humidity (RH) for 5 days, and/or by alkali deproteinisation and cysteine addition during Rapid Visco Analyser (RVA) pasting characterisation. Accelerated aging, deproteinisation and the reduction of disulfide bonds changed the RVA pasting curves of all Thai rice cultivars, particularly the waxy one (p < 0.05). This study has quantified the contribution of protein in relation to amylose on the RVA pasting profiles and demonstrated that protein and starch were in separated phases after heating. The continuity of the protein network in cooked non-waxy rice grains observed under confocal laser scanning microscopy (CLSM) indicated bi-continuous structure of starch and protein phases.