Studies on pressure parboiling of rice.

The long cooking time and hard texture of pressure-parboiled rice were investigated. Paddy adjusted to various moisture contents (12-30%) was steamed under different pressures (0-3 kg/cm-2) for different times (5-80 min). Translucence index (% rice area not covered by white belly), gelatinization index [equilibrium moisture content (EMC) attained by paddy immediately after steaming when soaked in water at room temp. (EMC-S)], retrogradation index (% fall in EMC-S of rice after drying and milling as compared to immediate EMC-S), cooking resistance index (% decrease in water uptake during cooking of parboiled as compared to raw rice), colour and head-rice recovery were studied. Degree of each property increased with increase in moisture content, pressure and time of steaming. Complete parboiling (100% translucence) could be achieved even at very low grain moisture (12-20%) when steamed under high pressure. However, such rice was too hard to cook. A translucence index of about 80% was the max. in pressure-parboiled rice that was acceptable in terms of cooking quality and colour. Its milling breakage was negligible. With this modification, pressure-parboiling process will be acceptable.