Polishing conditions in rice milling differentially affect the physicochemical properties of waxy, low- and high-amylose rice starch

Abstract

Effect of polishing condition during milling of rice on the properties of rice starch was investigated. Waxy, low- and high-amylose rice were polished with different milling speeds (750, 950 and 1050 r/min) and milling durations (20, 40 and 60 s) to obtain polished rice. Rice starches were extracted from the polished rice. Swelling power and solubility index of low- and high-amylose rice starches increased with milling speed and duration compared with unpolished rice starches. However, for waxy rice starch, there was no significant change. The peak, trough and final viscosities decreased for waxy rice starch and increased for high-amylose rice starch with increased polishing, whereas those of low-amylose rice starch increased first and then decreased. Polishing induced greater pseudoplasticity in starch relative to that from unpolished rice. Polishing duration during milling caused greater changes in swelling behavior and pasting properties, whereas polishing duration caused greater effects on structural properties. This study showed that both polishing speed and duration impacted the physicochemical and rheological properties of different rice starches, but to a different extent.