Extrusion of starch and water at temperatures above 100 C
leads to the formation of voids, due to the expansion of steam as
the extrudate exits at the high-pressure conditions of the die [4].
It can be divided into three mechanistic steps: nucleation, bubble
growth and bubble stabilization. Typical structure of the extruded
starch foam is presented in Fig. 2a. The foam cellular structure can
be significantly affected by extrusion conditions (i.e., barrel temperature,
die diameter, and screw speed), and material compositions,
(i.e., starch type, feed moisture, and nucleation agent
concentration), as reported in several works