Impacts of the Particle Sizes and Levels of Inclusions of Cherry Pomace on the Physical and Structural Properties of Direct Expanded Corn Starch

Abstract

An effort was made to understand the impacts of dried cherry pomace (by-product of cherry juice processing) inclusion into corn starch extrudates on their direct expansion characteristics. The effect of pomace particle sizes (whole unfractionated ( 500 μm), 500 μm) and levels of pomace inclusion (0, 5. and 15% (w/w)) were specifically investigated. Feed moisture content of 15.5 ± 0.5% (w.b.) and the extruder barrel temperature of 140 °C were kept constant with varying extruder screw speed (150, 200, and 250 rpm). The radial expansion ratio (ER) increased with 5% pomace level of inclusion compared with control but decreased significantly (p < 0.05) at 15% inclusion. Particle sizes significantly affected ER (p < 0.05) with smaller particle sizes resulting in increased ER at all levels of pomace. Adding cherry pomace significantly decreased water absorption index (WAI) and water solubility index (WSI) with smaller particles leading to higher WSI. Extrusion process did not reduce the total phenolic content (gallic acid equivalents). Inclusion of the smallest particle size (<125 μm) cherry pomace at 5% level of inclusion yielded extrudates with the highest expansion ratio among all treatments, including the control. The scanning electron images suggested improvements in the extrudate surface and the internal cell structures. The results indicated the presence of active interactions between the cherry pomace and starch during the expansion process which is not present as an inert material.