Production and properties of snack foods developed by extrusion from composite of barley, and tomato and grape pomaces

The barley flour and barley flour-pomace blends (tomato, grape) were extruded in a 30 mm APV co-rotating twin-screw extruder. Response surface methodology using a central composite design was used to evaluate the effects of independent variables, namely die temperature, screw speed for barley flour extrudates as well as pomace level for barley-pomace extrudates on system parameters (specific mechanical energy, die pressure and die melt temperature), physical properties (sectional expansion index and bulk density), color parameters (Hunter L, a, b and ? E), functional properties (water absorption and solubility indices), textural properties (peak force, slope and distance) and antioxidant activity and total phenolics, degree of gelatinization, in vitro starch digestibility and ? -glucan content. Selected samples of extrudates were evaluated sensorially in terms of appearance (color and porosity), taste (bran flavor, bitterness, sweetness and tomato flavor), off-odor, texture (hardness, crispness and brittleness) and overall acceptability by semi-trained panelists. In addition, total fiber content of some extrudates was determined. The system parameters and product properties were most affected by changes in temperature and to a lesser extent by screw speed and it was observed that those properties were also dependent on the changes of pomace level for barley-pomace blend extrudates. Extrusion cooking significantly reduced both antioxidant activities and total phenolics and increased digestibility of all extrudate samples. Results showed that the content of ? -glucan is higher in barley flour than in extrudates of barley flour and pomace blends.