Effects of Harvesting Period and Parboiling Condition on Nutritional Quality of Parboiled Rice

Abstract

Pre-mature harvesting of rice is sometimes forced by flooding—a consequence of global warming— which resulted in low rice quality. Parboiled rice production may be used to reduce this quality loss. The objective of this experiment was to determine how the harvesting period and parboiling condition affected the nutritional quality of parboiled rice and yield. Four rice varieties (Suphan Buri 1, Chai Nat 1, San-pah-tong 1 and RD10) were harvested from the field at five different stages (15, 20, 25, 30 and 45 days after flowering). The four rice varieties were used to test for yield from moisture reduction and weight. Yield tended to decrease when harvested early, and the highest yield was observed in Suphan Buri 1. After that, Suphan Buri 1 was used to test for parboiling conditions, consisting of: 1) soaking rice samples in deionized water at 60˚C for 5 hours, and 2) no soaking before steaming all samples in a pressure steamer at 0.8 kg/cm³ for 10 minutes. The samples were sun-dried and analyzed for nitrogen, zinc and iron concentrations. Rice parboiling without soaking before steaming resulted in higher zinc concentration in the rice grain than that of soaking in all harvesting periods. There was no difference in nitrogen and iron concentrations in the rice grain between the two parboiling conditions. Thereafter, rice parboiling without soaking was used to evaluate the effects of harvesting period on nutritional quality among the rice varieties. Nitrogen, zinc and iron concentrations in the parboiled rice grain were affected differently by rice variety and harvesting period, but without significant interaction between the two factors (except for zinc). San-pah-tong 1 had higher nitrogen, zinc and iron concentrations than those of other varieties. Meanwhile, harvests at 25 days after flowering had lower nitrogen, zinc and iron concentrations than those of other harvesting periods. The information in this study can be used as basic information for producing parboiled rice with high nutritional quality in areas where rice has to be prematurely harvested.