Development of small scale parboiling cum drying unit for paddy processing

Abstract

Parboiling is an optional unit operation in paddy processing, which results in enhanced milling efficiency with improved nutritional quality of the rice. It is accomplished through the process of soaking, steaming and drying, to gelatinize the starch. Technological advancement in the industrial parboiling has resulted in extensive improvisation of process controls in large-scale industrial parboiling units. But enormous initial investments required for infrastructure, along with the time, labour and energy involved in paddy parboiling made it uneconomical for small scale milling and processing units to undertake parboiling. In this scenario, a small scale parboiling cum drying unit with reduced drudgery and less human interventions was fabricated in this present study for paddy processing and its evaluation was done. The unit mainly consists of two soaking cum steaming chambers (100 kg/tank), LSU dryer, bucket elevator, steam boiler and heat furnace. Soaking and steaming was carried out in the same chamber and drying was carried out in the LSU dryer. The paddy crop variety Jyothi was parboiled at different soaking and steaming times (20, 25 and 30 min) and drying temperatures (50, 60 and 70 ° C) in both hot soaking and cold soaking methods. The performance evaluation of the developed unit was done by analysing the milling and cooking qualities of the parboiled paddy. The treatments were optimised using the Response Surface Methodology (Box Behnken) method. An increase in steaming time exerted a significant effect on milling and cooking qualities of parboiled paddy. The increase in drying time decreased the milling efficiency, head rice yield and hardness of the parboiled milled rice. After optimisation, for hot soaking, milling efficiency of 65.43% and head rice yield of 87.78% were obtained with a soaking time of 7 h, steaming time of 26.07 min and drying temperature of 52 ° C. In case of cold soaking, milling efficiency of 62.15% and head rice yield of 81.93% were obtained with a soaking time of 60 h, steaming time of 27 min and drying temperature of 52 ° C. The processing cost of parboiling one-kilogram paddy in the developed unit were Rs. 2.55/-. The benefit cost ratio for the parboiling process was found to be 1.33:1, which revealed that the developed unit was economically feasible.