ABSTRACT
Thermoplastic extrusion is a widely used industrial technology for continuous production of expanded products such as breakfast cereal and snack products (Alavi et al. 1999). The conventional method of steam pufng involves low in-barrel moisture contents (13-20%, wet basis) and high temperatures (130-170°C) and shear (Chinnaswamy and Hanna 1988; Harper and Tribelhorn 1992). These extreme conditions prevent utilization of heat-sensitive ingredients such as whey proteins, and certain avors and colors. Other disadvantages of high shear and temperature include costly barrel and screw wear, production of undesirable dextrins, increased losses in vitamin and amino acid availability, and starch degradation, which increases the water solubility of extrudates (Hauck and Huber 1989; Kirby et al. 1988). Typically, steam-expanded products have a coarse and very nonuniform cellular structure (Barrett and Peleg 1992) with cell sizes in the range of 1-3 mm and expansion ratios in the range of 9-12. Moreover, there is little or no control over cell size and density.
