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

Abstract

Laboratory scale studies were conducted to determine temperature distribution in the traditional parboiling process using a rice cooker. A sample holder with a wire-mesh bottom was used to keep the sample from the hot water. The material temperature and the qualities of parboiled rice (hardness, color, Iightness and head rice yield) were determined for different layers. The thickness of each layer was about 20 mm. The temperature distribution in this parboiling process (pre-steaming and steaming) was found to be uneven. The change of material temperature was faster for the first (bottom layer; beneath which steam started to penetrate the paddy mass), next was the second (middle) and last was the third (top) Iayer. The greater the thickness of the material, the lower was the material temperature. The hardness and the head rice yield were found to be the highest for the first, with the second and third layers following in that order; this might be affected by the material temperature. Difference in color intensity and lightness value was insignificant among the layers. The hardness, color intensity and lightness value were about 70 N, 24, and 57, respectively, corresponding to the maximum head rice yield (67 % , first layer) which is considered to be the suitable quality of parboiled rice.Keywords: traditional parboiling, temperature distribution, material temperature, quality of parboiled rice.Parboiling is the combined effort of soaking, steaming and drying and is widely used in some of the developing countries including Bangladesh, where parboiled rice is the staple food. Parboiled rice has been produced by both traditional and modern methods. Modern methods are energy and capital intensive, and are not suitable for a small-scale operation at the village level (Ali and Ojha, 1976;Bhattacharya, 1990). 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. Traditional parboiling processes use either single or double steaming. In single steaming, paddy is soaked in water of room temperature for a period of 36 to 72 h and in double steaming pre-steamed paddy is soaked in unheated water for 24 h. Various methods and devices are being used in the traditional parboiling process and produce parboiled rice of different grades. The device consists of pottery to boilers. The vessel (Fig. 1) is the most commonly used traditional parboiling device in villages (Roy et al., 2003a), where the paddy is subjected to double steaming. It has been reported that 20% of paddy is submerged in water during pre-steaming and steaming.The hot water parboils the submerged paddy and the rest is parboiled by steam generated in the system (Haque et al., 1997); this is con...

Effect of processing conditions on overall energy consumption and quality of rice (Oryza sativa L.)

“…Several researchers have studied the effect of DOM on the head rice yield, food components in rice, color, cooking qualities and insect infestation (Takai and Barredo, 1981;Sarker and Miyahara, 1984;Pike, 1994;Mohapatra and Bal, 2006;Mohapatra and Bal, 2007;Lamberts et al, 2007;Arora et al, 2007;Liang et al, in press;Yadav and Jindal, 2008). The energy consumption during individual operations of rice processing has also been reported by several researchers (Roy, 2003;Roy et al, 2004a;Mohapatra & Bal, 2007), where a power meter was used to measure energy consumption, but the effect of DOM on the overall energy consumption and food components in cooked rice has yet to be reported. Therefore, this study attempts to evaluate the effect of processing conditions (DOM) on overall energy consumption and quality of rice to determine whether the energy consumption during rice processing can be reduced while retaining more of the nutritional components in rice.…”

Energy consumption and cost analysis of local parboiling processes

“…The quality of the paddy, intensity of parboiling and degree of milling also affect the milling yield. The color and lightness of the rice are also closely affected by the material temperature and the degree of parboiling (Bhattacharya & Rao, 1966;Kimura, Bhattacharya, & Ali, 1993;Roy, Shimizu, & Kimura, 2004). Over-parboiling resulted in over-opening of the husk components followed by bulging out of the endosperm which initiates surface scouring during milling and the resultant ground particles being lost into the husk and bran.…”

Hydrothermal Carbonization of Peat Moss and Herbaceous Biomass (Miscanthus): A Potential Route for Bioenergy

“…The probe diameter and load cell were 5 mm and 5 kN, respectively. The test speed was controlled to 0.1 mm/s [37,38] and compressed to an extension of 2.5 mm. The pellet was horizontally placed at the center of the horizontal plate as well as the center of the probe to measure the peak force ( Figure 1) of a single pellet, which is considered to be the hardness of the pellet.…”