Keywords: twin screw extrusion, apple pomace, optimisation, response surface methodology, RSM, rice flour, extrudates, apple juice, moisture content, screw speed, die temperature, feed composition, nutritional snacks, snack food
Development and characterisation of apple pomace and rice flour–based extrudates
By–product generated from apple juice industry (apple pomace) was dried, milled and used as nutritionally rich ingredient for the preparation of rice flour–based extrudates. Response surface methodology was used to investigate the effects of extrusion conditions including moisture content (17–21%), screw speed (270–310 rpm), die temperature (110–130°C) and proportion of apple pomace in feed composition (10 to 30%). The lateral expansion, bulk density, water absorption index, water solubility index, hardness, colour and sensory characteristics were measured as responses. It was observed that lateral expansion ranged from 87.25 to 130.31%, bulk density from 0.22 to 0.29 g/cm³, water solubility index from 6.01 to 15.45%, water absorption index from 6.12 to 7.22 g/g, hardness from 22.35 to 38.87 N and overall acceptability from 5.41 to 6.56. The results suggest that apple pomace can be extruded with rice flour into an acceptable and low cost nutritional snack food.