Effect of Processing Conditions on Physical Properties of Parboiled Rice.

Abstract

A laboratory-scale parboiling setup was fabricated to produce parboiled rice at low steaming temperatures for determination of its physical properties, the quality indicators, and to compare those qualities with rice produced at higher temperatures. Parboiled rice was prepared under different steaming conditions using different sample sizes, both of which affected the rice temperature and quality. A sample size of 200 g, which maintained a 10 mm thick layer of rough rice, was found adequate for favorable quality. Better quality of parboiled rice was achieved at lower steaming temperatures (80-100˚C) than that at higher temperatures (110 and 120˚C). The temperature-time combinations of 80˚C-40 min, 90˚C-30 min and 100˚C-20 min were recommended steaming conditions. Parboiled rice produced under these conditions has adequate lightness and color intensity, 4.0 to 7.5% more milling yield having 55 to 80 N hardness values compared with an untreated sample. It is believed the proposed parboiling method would be seen as important by both household and commercial parboiling plants in their production of a good quality product.Keywords: parboiling setup, processing conditions, parboiled rice, physical propertiesThe parboiling process is a big share of the global rice processing industry. Generally, the majority of the population of a developing country consumes parboiled rice. This is especially true on the Indian Sub-continent where it originated a long time ago. It was reported that about one-fifth of the world's rice is parboiled (Bhattacharya, 1985). This seems to be increasing day by day, because the growth rate of populations in these countries is higher and a major part of the food value of what they consume comes from rice. Parboiling is a hydrothermic treatment given to rough rice, and consists of soaking, steaming and drying. During the parboiling process, starch gelatinization takes place, a thermochemical reaction between the starch granules and heat energy in the presence of water. This starch gelatinization changes the physicochemical properties of rice (Bhattacharya & Subba Rao, 1966;Bhattacharya & Indudhara Swamy, 1967;Raghavendra Rao & Juliano, 1970;Gariboldi, 1972;Kimura, 1983;Bhattacharya, 1985;Itoh & Kawamura, 1985;Kimura, 1991;Kimura et al., 1993;1995;Islam et al., 2001), which affects the other processing operations of storage, milling, cooking and eating quality. Islam et al. (2001) evaluated the quality of parboiled rice by its physical properties of maximum viscosity, hardness of brown rice, hardness and adhesion of cooked rice, volume expansion ratio and solid content, utilizing the first-order kinetic model. They identified the rate of change of quality and the quality index of parboiled rice with the reaction rate constant and final values of the quality indicators. The quality of parboiled rice was greatly affected by the severity of the parboiling treatment; severely treated rough rice produces a product of lesser quality. For wider acceptability of parboiled rice, processing equipment and co...

Effect of Processing Conditions on Thermal Properties of Parboiled Rice.

“…Interrelationship between the thermophysical properties of parboiled rice In a previous communication (Islam et al, 2002) the quantitative color values of 17.0 to 21.0 were reported as an index of the quality of parboiled rice for steaming temperatures of 80 to 100˚C. The better quality of parboiled rice was determined through the physical properties of hardness, milling yield, lightness and color values compared with the untreated sample.…”

“…In our previous communication (Islam et al, 2002) it was reported that a better quality of parboiled rice was achieved in the hardness value range of 55 to 80 N. The hardness value was measured using a compressional-elongational rheometer (Texture Analyzer TA-XT2, Stable Micro System, Surrey, England) according to Islam et al (2001). The average bio-yield point value (Mohsenin, 1980) of 25 determinations was expressed as the hardness of parboiled brown rice; Fig.…”

“…The starch gelatinization brings about changes in the physicochemical properties of rice (Raghavendra Rao & Juliano, 1970;Kimura, 1983;Bhattacharya, 1985;Itoh & Kawamura, 1985;Kimura, 1991;Kimura et al, 1993;Islam et al, 2001), which affects the other processing operations of storage, milling, cooking and eating qualities. Islam et al (2002) studied the effect of processing conditions on the physical properties, the quality indicators of parboiled rice: moisture content after steaming, hardness, milling yield, lightness and color value, produced at lower (80, 90 and 100˚C) and higher (110 and 120˚C) temperatures. They reported that parboiled rice produced at lower temperature provided a better quality product than that produced at higher temperatures.…”

Effect of Temperature Distribution on the Quality of Parboiled Rice Produced by Traditional Parboiling Process

“…Head rice yield Parboiling treatments gelatinize the rice starch, improve the hardness of parboiled rice, and minimize the breakage loss during milling, which consequently increases head rice yield (Kimura et al, 1995;Islam et al, 2002). The head rice yield was increased with an increase of material temperature for all layers up to a certain level (90'C), which is considered to be the optimum material temperature for traditional parboiling.…”

“…In Bangladesh, more than 80~~O of the rice is processed in villages and less than 20% in commercial rice mills (Rahaman et al, 1996). In the modern parboiling processes, the paddy is soaked in hot water for a period of 3 to 6 h at 55 to 70'C (CFTRI, 1969;Tiwary and Ojha, 198 1 ;Kimura, 1989;Islam et al, 2002). For steaming, steam is generated in the boiler and is applied to the soaked paddy in hoppers through connecting pipes.…”