Parboiled rice (also called converted rice and easy-cook rice) is rice that has been partially boiled in the husk. The three basic steps of parboiling are soaking, steaming and drying. These steps make the rice easier to process by hand, while also boosting its nutritional profile, changing its texture, and making it more resistant to weevils. About 50% of the world's paddy production is parboiled. The treatment is practiced in many parts of the world such as India, Bangladesh, Pakistan, Myanmar, Malaysia, Nepal, Sri Lanka, Guinea, South Africa, Italy, Spain, Nigeria, Thailand, Switzerland, USA and France.
Rice is easier to polish by hand (removal of the bran layer) after parboiling but mechanical processing is harder since the bran becomes somewhat oily and tends to clog machinery. Most parboiled rice is milled in the same way as white rice.
Parboiling drives nutrients, especially thiamin, from the bran to the endosperm, hence parboiled white rice is mostly nutritionally similar to brown rice. Because of this, parboiling was adopted by North American rice growers in the early 20th century.
Process and chemistryEdit
The starches in parboiled rice become gelatinized, then retrograded after cooling. Through gelatinization, amylose molecules leach out of the starch granule network and diffuse into the surrounding aqueous medium outside the granules which, when fully hydrated are at maximum viscosity. The parboiled rice kernels should be translucent when wholly gelatinized. Cooling brings retrogradation whereby amylose molecules re-associate with each other and form a tightly packed structure. This increases the formation of type 3-resistant starch which can act as a prebiotic and benefit good health in humans. However, this also makes the kernels harder and glassier. Parboiled rice takes less time to cook and is firmer and less sticky. In North America parboiled rice is either partially or fully precooked before sale. Minerals such as zinc or iron are added, increasing their potential bio-availability in the diet.
In older methods, clean paddy rice was soaked in cold water for 36–38 hours to give it a moisture content of 30–35%, after which the rice was put in parboiling equipment with fresh cold water and boiled until it began to split. The rice was then dried on woven mats, cooled and milled.
In the 1910s German-British scientist Erich Gustav Huzenlaub (1888–1964) and the British scientist and chemist Francis Heron Rogers invented a form of parboiling which held more of the nutrients in rice, now known as the Huzenlaub Process. The whole grain is vacuum dried, then steamed, followed by another vacuum drying and husking. This also makes the rice more resistant to weevils and lessens cooking time.
In even later methods the rice is soaked in hot water, then steamed for boiling which only takes 3 hours rather than the 20 hours of traditional methods. These methods also yield a yellowish color in the rice, which undergoes less breakage when milled.
|Nutritional value per 100 g (3.5 oz)|
|Energy||370 kcal (1,500 kJ)|
|Dietary fiber||3.5 g|
|†Percentages are roughly approximated using US recommendations for adults. |
Source: USDA Nutrient Database
Compared to brown rice, parboiling of rice incurs losses of thiamin, niacin, biotin, and pantothenic acid by approximately 70%, 28%, 49% and 25%, respectively. Compared to normal milling, which causes a near 65% loss of all these micronutrients, parboiling preserves more of them. The specific loss depend on the process used by individual manufacturers: for the USDA #20042 sample, much less loss in these nutrients is observed. Fortification is common for parboiled rice in the United States.
- Miah, M., Haque, A., Douglass, M., & Clarke, B. (2002). Parboiling of rice. Part II: Effect of hot soaking time on the degree of starch gelatinization. International Journal of Food Science & Technology, 37(5), 539-545. doi:10.1046/j.1365-2621.2002.00611.x
- M.C. Kik and R.R. Williams, "The Nutritional Improvement of White Rice", Bulletin of the National Research Council 112 (June 1945) p. 61ff
- Pillaiyar, P. (1981). Household parboiling of parboiled rice. Kishan World, 8, 20–21.
- Kyritsi, A.; Tzia, C.; Karathanos, V.T. (January 2011). "Vitamin fortified rice grain using spraying and soaking methods". LWT - Food Science and Technology. 44 (1): 312–320. doi:10.1016/j.lwt.2010.06.001.
- Hermansson, Anne-Marie; Svegmark, Karin (November 1996). "Developments in the understanding of starch functionality". Trends in Food Science & Technology. 7 (11): 345–353. doi:10.1016/S0924-2244(96)10036-4.
- Eliasson, A.C. (1986). Viscoelastic behaviour during the gelatinization of starch. Journal of Texture Studies, 17, 253–265. doi:10.1111/j.1745-4603.1986.tb00551.x
- Helbig E, Días AR, Tavares RA, Schirmer MA, Elias MC (June 2008). "Arroz parboilizado efeito na glicemia de ratos Wistar" [The effect of parboiled rice on glycemia in Wistar rats]. Archivos latinoamericanos de nutricion (in Portuguese). 58 (2): 149–55. PMID 18833992.
- Ali, Z. S. and Ojha, T. P. (1975). Soaking characteristics of paddy. Journal of Agric.Engineering. Res. (20) 4, 353.
- US patent 2358251, Huzenlaub Erich GustavRogers Francis Heron, "Process for the treatment of rice and other cereals", issued 1944-09-12
- Ituen, E.U.U.; Ukpakha, A.C. (2011). "Improved method of parboiling paddy for better quality rice". World Journal of Applied Science and Technology. 3 (1): 31–40.
- Müller-Fischer, Nadina (2013). "Nutrient-focused Processing of Rice". Agricultural sustainability: progress and prospects in crop research. Academic Press. doi:10.1016/B978-0-12-404560-6.00010-1. ISBN 9780124045606.
- Arendt, Elke K.; Zannini, Emanuele (2013). "Rice processing". Cereal grains for the food and beverage industries. Woodhead Pub. doi:10.1533/9780857098924.114. ISBN 9780857094131.