A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1998

The quality of raw rice may be adversely affected by weather and environment conditions before, during and after harvesting. Parboiling is known as a means of improving the quality of raw paddy which has been subjected to poor handling. In this study, the effect of initial conditions of raw paddy on the quality of parboiled rice was investigated from two Indica varieties, namely Chinat and RD-23. The initial conditions of paddy were altered, (1) by successive moisture content rewetting the paddy by spraying water at 3 different moisture content levels (16%, 20% and 24% wb) followed by drying, (2) by overdrying the paddy to 12%, 10% and 8% wb, and (3) by rewetting the paddy from 13.5% to 20% wb and then delaying drying by 0, 2, 4 and 6 days. The changes in quality of parboiled rice for all paddy samples were determined and compared with that of the control in all cases. Results showed that repeated rewetting of raw paddy led to reduced yields of both milled and head rice both from the control and parboiled paddy. The influence of overdrying on the head yield reduction of parboiled rice was very small. Whiteness of the milled non parboiled rice reduced successively with number and degree of rewetting. Conversely, the hardness increased with these for milled parboiled rice. Hardness of cooked non-parboiled rice was not affected significantly by initial conditions of the raw paddy. However, hardness of cooked parboiled rice reduced with degree of overdrying and repeated rewetting treatments. The delay in drying of rewetted raw paddy did not seem to influence milled yield, head yield and hardness of both non-parboiled rice and parboiled rice. However, the whiteness increased with delaying time for non-parboiled rice, and did not change significantly for parboiled rice.