Effect of Shear Energy on Size Reduction of Starch Granules in Extrusion

Abstract

The changes of size and size distribution of starch granules under extrusion conditions have been investigated by using a single screw extruder and an optical microscope coupled with an image analysis system. The mechanical energy input and material processing time were key factors influencing the degree of starch granular size reduction. In a high shear extrusion process (T=40°C), the weight-average granular size of extrudate was reduced from -1 2 . 4~ (raw waxy corn starch) to 1-2p, whereas in a low shear extrusion (T=9OoC), the granular size was reduced to -7,u. Fine particles (<O.Sp) were observed in both extrusion processes. They were 76% (w/w) under a high shear and long processing time conditions and 5% in a low shear and short time process. During the size reduction process, the peaks of size distribution of starch granules shifted from the large size region toward the medium size region and finally to a rather narrowed peak at the small size region when extensive size reduction measures were applied. Extrusion processes can be used to reduce starch granular size effectively. Einflu6 von Scherenergie auf die GrMenreduktion von Starkekornern durch Extrusion. Die Veranderungen der GroBe und Korn-groBenverteilung von Starkekornern unter Extrusionsbedingungen wurden durch Venvendung eines Einwellenextruders und eines optischen Mikroskops mit einem Bildanalysensystem untersucht. Der mechanische Energie-Input und die Material-Bearbeitungszeit waren Schliisselfaktoren, die den Grad der Reduzierung der Starkekorngro-Oen beeinfluoten. In einem Hoch-Scher-Verfahren (T=4OoC) wurde die Gewichts-Durchschnitt-KorngroOe des Extrudats von -12,4,u (rohe wachsige Maisstarke) auf 1-2p, reduziert, wahrend bei einer Niedrig-ScherExtmsion (T=90aC) die KorngroBe auf -71 reduziert wurde. Feine Partikel (~0 . 5~) wurden bei beiden Extrusions-Verfahren beobachtet. Sie betrugen 76% (w/w) unter hoher Scherung und langen ProzeBzeit-Bedingungen und 5% bei einem Niedrig-Scher-und Kurzzeit-Verfahren. Wahrend des GroBenreduktions-Verfahrens verscho-be11 sich die Peaks der GroBenverteilung der Stiirkekorner von dem GroBkornbereich in Richtung des mittleren Bereichs und schlie5lich zu einem ziemlich angenahertem Peak im Kleinkornbereich, wenn extensive ReduktionsmaBnahmen angewandt worden waren. Extrusionsverfahren konnen wirksam zur Reduktion der Starkekorn-GroBe angewendet werden. starchlsrdrke 47 (1995) Nr. 4, S. 151-156 VCH Verlagsgesellschd mbH, D-69451 Weinhelm. 1995 0038-9056/95/0404-01~l$05.00+.25/0

Physical and thermal properties and X-ray diffraction of corn flour systems as affected by whole grain wheat flour and extrusion conditions

“…The SME ranged from 84 to 154.67 Wh/kg, similar to the values found by Moraru and Kokini (60–170 Wh/kg) in a study with whole wheat extrudates working at a higher range of barrel temperatures (120 or 180°C) and similar feed moisture (18 or 22%). The SME is a good quantitative descriptor in extrusion processes of the extent of macromolecular transformations and interactions that take place, i.e ., starch conversion, and consequently, the rheological properties of the melt . Higher SME usually results in a greater degree of starch gelatinization, greater extent of starch molecular size reduction and extrudate expansion .…”

“…Gelatinization temperature ranges for CF and WGWF were 65.25-78. 25 and 56.76-69.95°C, respectively. Some displacement in the peak temperatures, giving narrow peaks, was observed in the 50% blend.…”

Advanced Nano-biocomposites Based on Starch

“…3.1), shear forces can physically destructure starch granules, allowing faster transfer and distribution of water into the material (Burros et al 1987). Therefore, during extrusion, the loss of the crystallinity is not only caused by the water penetration but also by mechanical disruption due to the intense shear fields within the extruder (Barron et al 2001;Wang and Zheng 1995;Zheng and Wang 1994;Zheng et al 1995).…”

Rheology to understand and optimize processibility, structures and properties of starch polymeric materials

“…In extrusion processing, shear forces can physically tear apart the starch granules, allowing faster transfer of water into the interior molecules [33]. Therefore, during extrusion, the loss of crystallinity is not only caused by water penetration, but by the mechanical disruption of molecular bonds due to the intense shear fields within the extruder [34][35][36][37].…”