Journal paper CAFST 98025, Korea University, Seoul, Korea.
Graduate School of Biotechnology, Korea University, Sungbuk-ku, Seoul 136-701, Korea.
Department of Food Science and Technology, Kongju National University, Choongnam 340-800, Korea.
Corresponding author. Phone: 02-3290-3435; Fax: 02-927-5201; E-mail: firstname.lastname@example.org.
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Accepted September 8, 1998.
Corn starch was extruded with a corotating twin-screw extruder (24:1 L/D ratio, 31-mm screw diameter) and supercritical CO2 was injected as a blowing agent. The effects of barrel temperature (80–90°C), screw speed (150–250 rpm), and water injection (30–54 g/min) on specific mechanical energy (SME) input for the process and the physical properties of extrudates, such as expansion ratio, water absorption (WA), water solubility (WS), breaking stress, and elastic modulus, were examined using a response surface methodology. Barrel temperature had the greatest effect on physical properties of extrudates but not on SME input, whereas screw speed and water injection had significant effects on SME input. Extrudates had a smooth surface, and air cells were uniform and closed, providing low WA and WS. Using superimposed contour plots, optimum barrel temperature, screw speed, and water injection rate, based on maximum expansion ratio and minimum SME input, were 94–96°C, 155–175 rpm, and 36–39 g/min, respectively.
© 1999 American Association of Cereal Chemists, Inc.