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Extrusion processing of non-waxy and waxy barley flour to produce puffed cereals. L. T. NGUYEN
and B.-K. Baik. Washington State University, Department of Food Science and Human Nutrition, Pullman,
WA 99164-6376.
Roller-milled flours from two non-waxy and two waxy barley cultivars
were granulated to facilitate feeding and flow through the barrel and extruded to form expanded, puffed
products using a modified laboratory single-screw extruder. Effects of die diameter, moisture content, screw
speed, barrel temperature and feed rate on the physical properties of barley extrudates were determined.
Break flours of both non-waxy and waxy barleys exhibited a higher expansion ratio (2.70 to 3.02) and lower
hardness than reduction flour. In comparison, non-waxy barley produced more expanded and less dense, but
firmer extrudates than waxy barley. Overall, the pressure and torque during extrusion were significantly
higher in non-waxy than in waxy barley. As the moisture content of barley granulates decreased from 21 to
16%, the expansion ratio of extrudates increased from 1.83 to 2.16 and hardness decreased from 69.8 to
32.4 N*s. Changing the screw speed from 50 to 150 rpm resulted in a higher expansion ratio for non-waxy
and waxy barley and increased hardness from 100.0 to 301.2 N*s in non-waxy and from 70.3 to 129.7 N*s
in waxy barley. Compared to barrel temperatures of 130, 150, and 170°C for the feeding, compression and
metering sections respectively, a constant barrel temperature of 160°C for the three sections produced
higher expansion in non-waxy barley, lower expansion in waxy barley.
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