Physical and sensory characteristics of Ready-To-Eat food prepared from finger millet based composite mixer by extrusion

Abstract

Extrusion cooking process is a high temperature and short time process in which moist, soft food material is fed to the extruder for desired temperature, pressure, and residence time.  Finger millet being a “nutricereal” was used to develop Ready-To-Eat (RTE) snack food through extrusion cooking.  Seven composite mixes were prepared using brown finger millet flour, maize flour, rice flour, full fat soy flour, bengal gram flour, and skimmed milk powder in varying proportions.  Extrusion cooking was carried out using a Twin Screw Extruder at a temperature of 140℃, screw speed of 300 r min^-1 and die diameter of 3 mm.  Physical properties of the extrudates namely bulk density, expansion ratio, Water Absorption Index (WAI), Water Solubility Index (WSI), colour and hardness were analyzed.  Organoleptic qualities of the extruded products were also analyzed.  The results indicated that the bulk density ranging from 0.1618 to 0.3946 g cm^-3 while expansion ratio varied between 2.42 and 3.50.  The water absorption index of the extrudates varied from 3.96% to 6.87%.  The mix containing the least amount of finger millet flour (10%) had the lightest colour (highest L value) as indicated by Hunter Colour Flex Meter while the composite mix with the highest amount of brown finger millet flour (40%) had the least value for hardness as indicated by Food Texture Analyzer.  The mean scores of organoleptic evaluation showed that all the extruded products prepared from the seven composite mixes were within the acceptable range.  It is found that the composite mix comprising of brown finger millet flour, maize flour, rice flour, and full fat soy flour in the ratio of 20:50:20:10 produced the most acceptable RTE extrudates in terms of expansion ratio (3.5), hardness (23.37 N) and sensory characteristics (8.87).

Keywords: extrusion, water absorption index, hardness, expansion ratio