Characterisation of brown and milled yellow rice and development of an expanded snack

Brown rice and yellow milled rice were characterised in relation to milling properties, cooking, processing quality and microbial testing, and utilised to develop an expanded snack. The extrusion process was done in a Mapimpianti single screw cooker-extruder. A flour sample feed rate of 70 g (dry matter) min(-1) was maintained by varying the force-feeder speed. A screw speed of 150 rev min(-1) and a die with 20 die-nozzle orifices (2 mm in dia) were used. The die zone was heated at 110 degrees C by electrical resistance. Compressed air was circulate around the barrel to maintain precise control of the temperature. The moisture content of the samples was 120, 150 and 180 g kg(-1). The grains were classified as long-thin with an average size of 2.13 mm x 6.79 mm. The milling yields obtained in the laboratory with paddy rice were 700 g kg(-1) brown rice and 600 g kg(-1) milled rice. Brown rice and yellow milled rice had similar amylose contents, 225 and 256 g kg(-1), respectively. Gel consistency was soft with low gelatinisation temperature (63-68 degrees C) for both samples. Field fungi such as Helminthosporium oryzae and storage fungi as Aspergillus spp were present in paddy, yellow milled and commercial rice. Helminthosporium oryzae was not present in extruded products. The extruded products showed low density and a high degree of expansion, with the optimum degree of expansion obtained in hours processed with moisture at 150 g kg(-1) in both milled and brown rice. The highest values for water solubility index were obtained with hours from milled yellow rice and none of the extruded products showed significant differences on water absorption index. Sensory analyses carried out on the snack products showed them to be acceptable, with the bent acceptance for products made from milled yellow rice processed with 150 g kg(-1) moisture.