Vol.4, No.9B, 12-22 (2013) Agricultural Sciences http://dx.doi.org/10.4236/as.2013.49B003 Copyright © 2013 SciRes. OPEN ACCESS Optimisation of extrusion cooking conditions and characterization of rice (Oryza sativa)—Sweet potato (Ipomoea batatas) and rice-yam (Dioscorea alata) based RTE products Elina Brahma Hazarika, Anjan Borah, Charu Lata Mahanta * Department of Food Engineering and Technology, School of Engineering, Tezpur University, Assam, India; * Corresponding Author: charu@tezu.ernet.in Received June 2013 ABSTRACT Extrusion cooking has been extensively used to produce variety of foods like ready to eat break- fast cereals, baby foods, snack foods, etc. Tak- ing rice flour as the base ingredient, two locally available tuberous root vegetables, greater yam (Dioscorea alata) and sweet potato (Ipomoea ba- tatas) were used in this study for the develop- ment of ready-to-eat breakfast products in a sin- gle screw extruder. During extrusion cooking, the screw speeds ranged from 132 to 468 rpm and the barrel temperatures ranged from 103˚C to 137˚C. The extrudates were then analyzed for various physical and physicochemical proper- ties. Optimization was done following Response Surface Methodology (RSM) using Central Com- posite Design. Using screw speed, barrel tem- perature and feed composition as the three in- dependent variables, the three responses taken were bulk density, expansion index and breaking strength. The optimized conditions were used for developing 3 new products one of which also contained tomato pulp powder. The products were analyzed for their physical, proximate, sensory and antioxidant properties. There was significant colour change in all the three samples as indi- cated by total colour change ( ∆ E). Texture anal- ysis of the extrudate samples showed hardness values ranging from 28.68 N to 47.57 N. Amylose content was found to be 15.3% in rice-sweet potato extrudate, 14.7% in rice-yam extrudate and 18.2% in rice-sweet potato-tomato extrudate. The antioxidant profile of the extrudates studied through DPPH (2,2-diphenyl-picryhydrazyl) sca- venging activity and FRAP (ferric reducing an- tioxidant property) showed that the antioxidant capacity in all the 3 extrudates was very low. Rice flour incorporated with sweet potato was judged the best on sensory evaluation. The study has shown that both sweet potato and greater yam tubers can be commercially exploited for the development of ready-to-eat (RTE) products. Keywords: Extrusion; RSM; RTE; Physicochemical Properties 1. INTRODUCTION Consumers want snacks that taste good, smell good, feel good, look good and in addition, are nutritionally su- perior and healthy. Extrusion cooking is one of the most important food processing technologies which have been used since the mid 1930s for the production of breakfast cereals, ready to eat snacks, and other textured foods. In the past decade, extrusion cooking has been studied ex- tensively to produce variety of specialty foods including pasta products and ready to eat breakfast cereals, baby foods, snack foods, texturised vegetable protein, pet foods, dried soups and dry beverage mixes, as it not only im- proves digestibility (Singh, Dartois, & Kaur, 2010) but also improves the nutrients bioavailability (Gu, Hous Rooney, & Prior, 2008) compared to conventional cook- ing. The quality of the product depends on the process conditions, such as the extruder type, the feed moisture, the temperature profile in the barrel sections, the screw speed and the feed rate (Thymi, Krokida, Pappa & Ma- roulis, 2005). Owing to the popularity and high nutritive value of vegetables, their utilization has increased either in raw form or processed form. Greater yam (Dioscorea alata) and sweet potato (Ipomoea batatas) are two species of large underground tuberous root vegetables seasonally available and are gaining importance as processed food