Effect of ultra-high pressure on quality characteristics of parboiled rice

Abstract

Quality characteristics of parboiled rice pre-treated by ultra-high pressures (UHP, 100–600 MPa) were investigated in this study. The LF-NMR results and morphologies of parboiled rice grain showed that UHP treatment promoted uniform distribution of water in rice grain and effectively eliminated “white-core” grain. The total colour difference (ΔE*) increased with increasing treatment pressures. DSC results showed that onset gelatinization temperature (To) of rice flour was increased after soaking but decreased after UHP treatment. And the degree of starch gelatinization (DSG) presented an increase at 100 and 200 MPa, but opposite trends were found at 200–600 MPa. Scanning electron microscopic images showed that the morphology of starch in rice changed a little after UHP treatment but lost polygonal shape after steaming. RVA results showed that the viscosity of rice flour increased after soaking and whether rice flour or parboiled rice flour's viscosity decreased with increasing pressures.