Effects of operating conditions on oil loss and structure of almond snacks


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An almond-and-wheat blend (about 1:2.5, dry basis) was extruded through a co-rotating twin-screw extruder with a barrel diameter of 25 mm. The effects of barrel temperature (69.77–120.23 °C), dough moisture (26.64–33.36%) and screw speed (13.85–38.50 rad s−1) on specific mechanical energy, oil loss that occurs during extrusion process, pressure at the die and on complexing index, break strength, porosity and expansion ratio of extrudates were investigated using response surface methodology. The only variable that had a significant influence on oil loss was barrel temperature (the lowest oil loss, i.e. 0.06%, was obtained with the minimum barrel temperature). The worst product structure was obtained at barrel temperature less than 100 °C. Yet, the highest values of porosity (18.47%) and expansion ratio (158.76%) were obtained at a barrel temperature of 120 °C. Regression results showed a positive correlation (r2 = 0.94) between oil loss, porosity and expansion degree values.