Parboiling of rice. Part I: Effect of hot soaking time on quality of milled rice

Abstract

This study investigated the effect of soaking time on the quality of parboiled rice. The paddy was soaked in water at 25 and 80 °C for 15, 30, 45, 60 and 120 min. The soaked paddy was steamed, dried, stored and milled. With increasing soaking time a significant increase in water absorption and milling and head rice yield (hence reduction in broken rice) was observed. A significant difference in milling yield, at the 1% level, was obtained between the raw rice control and the hot soaked parboiled samples. A large reduction in fissured grain was observed after soaking. It is suggested that parboiling fills the void spaces and cements the cracks inside the endosperm, making the grain harder and minimizing internal fissuring and thereby breakage during milling.

Comparative 3D simulation on water absorption and hygroscopic swelling in japonica rice grains under various isothermal soaking conditions

“…Higher soaking temperatures have known to cause expansion and softening, thus reducing the diffusion resistance. The softening of cereal grains was also reported in milled rice and white rice (Kashaninejad et al, 2007;Miah, Haque, Douglass, & Clarke, 2002;Sowbhagya, Ramesh, & AIi, 1994). Genkawa et al (2010) also showed that after 10 min of soaking, the breaking load or rigidity of rice had decreased by about 23 N upon changing the soaking temperature from 15°C to 25°C.…”

Key factors affecting Fe density in Fe-fortified-parboiled rice: Parboiling conditions, storage duration, external Fe-loading rate and genotypic differences

“…The penetration of added Fe into white-parboiled rice in this study was enhanced by soaking at elevated temperature (60°C), probably due to decreased resistance of water penetration across cell layers of the endosperm and/or enhanced ion exchange, even in a shorter time. Moreover, soaking of paddy rice at room temperature over a long period also carries the risk of deterioration of flavour from fermentation (Islam, Shimizu, & Kimura, 2002;Miah, Haque, Douglass, & Clarke, 2002).…”

High pressure induced water uptake characteristics of Thai glutinous rice

“…Higher temperatures are known to expand and soften grains. Temperature induced softening has been reported for soybean (Singh & Kulshrestha, 1987), chickpea (Hung, Liu, Black, & Trewhella, 1993), kidney bean (AbuGhannam & McKenna, 1997), wheat (Maskan, 2002), rough rice (paddy) and milled rice (Miah, Haque, Douglass, & Clarke, 2002;Sowbhagya, Ramesh, & Ali, 1994). Soaking temperatures closer to the gelatinisation temperature of starch, resulted in greater water uptake.…”