Snack food development with single phase extrusion-cooking technology
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Extrusion cooking technology is a popular technique for generating a wide range of ready-to-eat products, from snacks, breakfast cereals, pasta and instant noodles to pet food. Extrusion cooking involves inserting raw materials – minimally starchy grains and water – at one end of an extruder barrel. The starch-based raw materials are conveyed through the barrel, typically by a worm drive, to an exit die that forms the final shape. The high pressure, shear forces and friction that develop towards the die end of the extruder generates heat which cooks the product, in turn producing an extruded dry, shelf stable product. Existing commercial extruders require a three-phase power supply to run the high torque motors, which, are used to provide enough energy to generate the amount of pressure and forces required for industrial production. Millbank Group of Mangere, Auckland has developed a single phase extruder. The advantage of using a single phase powered extrusion cooker is that ready-to-eat snacks can be produced on site by cafes, restaurants or even cinemas, which seldom have a three-phase power supply. Disaster relief is another application, where portable generators are most commonly single phase. The primary objective of this research is to create products and evaluate their physiochemical properties and to evaluate is consistent viable products can be produced using single phase power. The first phase of this study was to produce, analyse and compare the extrudates created by this single phase extrusion cooker by using maize, wheat and brown rice as the primary grains. In the second phase of this study, new grains were introduced to create some new combinations. They were peanut, oat, mung bean, soy and amaranth. Although the addition of the new grains was in a relatively low ratio, ranging from 5 to 10%, they brought a huge impact on the extrudates texture and bulk density. Extrusion cooking is a rapid yet complex process. There are process parameters, such as screw speed and nose temperature, that impact on the outcome of the extrudate properties which include texture and bulk density. The performance parameters data from Phase 1 and 2 showed variation from a statistical perspective, either due to subtle changes to the extruder and/or changes to the grain specifications. Therefore in the third phase of this study, a designed experiment was conducted which focused on the nose temperature on three basic grains that were often used in Phase 1 and 2, which were brown rice, maize and wheat, to examine whether the physicochemical aspect and texture of the extrudates would be different under the controlled nose temperatures. It was concluded that the higher nose temperatures significantly decreased the moisture content of all extrudates while the lower nose temperatures made the extrudates more difficult to break.