Development and Evaluation of a Pulse Polisher

Polishing is one of the important operations in dal milling process. In pulse polishing the dust or loose small particles and irregugularity of the surface is removed and the original colour is achieved. Polishing gives the shining to the dal thus improving its eye appeal and economics. A flap conveyer type pulse polisher was developed and evaluated. The milling experiment was conducted in the CIAE dal mill for pigeon pea pulses using CIAE method of pre treatment. The head dal obtained was under taken for the polishing study. The polisher was operated at 180 rpm. During this study the dal was fed at the hopper, which goes to the continuously moving shaft connected with the flaps. Tank is connected with the inlet of the pulse polisher through pipe and nozzle to drop water and linseed oil continuously @ 2% to the pulses. The dal mixed with the water/oil moved from the feeding end to the out let by the rotational action of the conveyer flaps and the pulse get polished by the abrasion between the flaps and the outer cylinder and within the pulses. The polished dal is collected from the out let. The unpolished and polished dal sample was taken and analyzed for its visual/organoleptic evaluation, colour using Hunter colour Lab and surface characteristics using Phase Contras Microscope. The organoleptic evaluation was carried out using 9 point Hedonic scale. The different dal samples were provided to the panel of judges for its evaluation by giving score on the basis of appearance, shining and regularity of the surface of dal. The polished dal received significantly higher score as compared to unpolished. The samples of head and polished dal were taken for the measurement of color using Hunter Lab (Lab Scan XE, Model No. LX16244, Hunter Associates Laboratory, Virginia) in terms of CIE ‘L*’ (lightness), ‘a*’ (redness and greenness), ‘b*’ (Yellowness and blueness), YI (Yellowness Index) and WI (Whiteness Index). The color values in terms of L*, a*, b*, YI, WI were found to be 60.61, 6.78, 28.26, −148.37 and 69.67 for unpolished dal 58.36, 8.04, 38.41, −240.70 and 93.96 for polished with water and 52.53, 9.97, 41.13, −247.91 and 98.79 for polished with oil respectively were obtained. Hence by polishing, the Yellowness and Yellowness Index has increased which indicated that the desirable colour, appearance and regularity of the surface of the pigeon pea dal has improved to a greater extent in terms of consumer acceptance. However the oil treated polished dal produced better results because of the presence of vex and lubricant nature of oil. The capacity of the pulse polisher was 200 kg/h.