Enhancing an Extruded Puffed Snack by Optimising Die Head Temperature, Screw Speed and Apple Pomace Inclusion

Extrusion cooking is recognised as a smart technology for food processors. It requires low cost, high temperature, short-time process and few ingredients to create a puffed snack. The only drawback is that it contains multiple parameters that need to be rigorously trialled to develop an optimal process. This study investigated the effects of two extruding parameters (die head temperature and screw speed) and examined the addition of apple pomace into a corn flour-based extruded snack formulation. A response surface design was utilised. A D-optimal design was chosen, which generated 21 combinations; within these combinations, the control formulation existed. Extrudate characteristics, i.e. bulk density and porosity, textural properties, cooked starch properties and moisture, were analysed. Screw speed was found to have the greatest effect on extrudate quality, e.g. bulk density increased as the screw speed increased (p < 0.001). Both apple pomace addition and screw speed impacted expansion ratio; as they increased, expansion decreased (p < 0.0001). The optimised and validated formulation contained the following parameter levels: 7.7 % apple pomace, 150 A degrees C die head temperature and a screw speed of 69 rpm. As apple pomace and corn flour are naturally gluten free, the extruded product would appeal to people who suffer from intolerances, allergies and coeliac disease.