Effects of Cultivar and Processing Condition on Physicochemical Properties and Starch Fractions in Parboiled Rice

Starch can be classified into rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) according to its resistance to amylolytic enzymes. This study investigated the effects of cultivar and feedstock under varying parboiling conditions on the physicochemical properties and starch fractions of parboiled rice. Rice (rough or brown) was soaked, steamed under pressure, dried immediately or stored at room temperature for 24 hr prior to drying, and then treated with or without a repeated steam cycle prior to milling. The storage treatment significantly increased the retrograded amylopectin enthalpy and amylose-lipid complex melting temperature of parboiled rice. Parboiled rice samples prepared from brown rice feedstock had higher peak melting temperatures but lower enthalpy values of retrograded amylopectin than samples prepared from rough rice after the storage treatment. The pasting viscosity of parboiled rice was most affected by the repeated autoclaving treatment and cultivar. Starch fractions in parboiled rice were significantly affected by cultivar and storage and by the interactions of cultivar and parboiling conditions. The storage treatment significantly increased SDS and generally decreased RDS in parboiled rice. Parboiled rice with different SDS and RS contents can be produced by varying rice cultivar and parboiling conditions.