Influence of process parameters on physical properties and specific mechanical energy of healthy mushroom-rice snacks and optimization of extrusion process parameters using response surface methodology.

Ready-to-eat healthy mushroom-rice snacks were developed and processed using twin-screw extruder. A 15% of oyster mushroom power could be added to improve the nutritional values of the rice based snack. The effects of process parameters (feed moisture, screw speed and barrel temperature) on physical properties and Specific Mechanical Energy (SME) during the production were investigated. Feed moisture was varied at 12-18% wet basis and the screw speed was studied in the range of 275-425 rpm, while the barrel temperature was operated at 130-150 °C. The result indicated that bulk density differed significantly with changes in all the process parameters. An increasing barrel temperature caused higher expansion ratio, while hardness of snacks increased due to an increase of feed moisture and a decrease of screw speed. SME was considered by measuring the electric current and voltage of the extruder. As a result, feed moisture demonstrated the most influence on the SME. Feed moisture between 12 and 15% wet basis, the SME decreased with decrease in feed moisture. On the other hand, the SME decreased when the higher feed moisture was operated in the range of 15-18% wet basis. In addition, the process condition was optimized using response surface methodology. From this study, the optimum extrusion-cooking conditions with respect to the physical qualities of snacks and SME during extrusion was 13.5% of feed moisture, screw speed of 425 rpm and maximum barrel temperature at 130 °C, since these conditions provided a good quality mushroom-rice snacks and consumed low SME.