Influence of Grape Pomace Inclusion on Physical and Chemical Properties of Corn-Based Extrudates

Abstract

This study investigated the feasibility of using grape pomace (GP) as a source of dietary fiber (DF) and polyphenol for extruded corn-based product and evaluated the impacts of GP level on the physical properties and chemical composition of extrudates. A 4x3 two-factor factorial design was used to for extrusion experiment. The two factors were the level of GP inclusion (0, 2.5, 5.0 and 10%) and moisture content (13, 15 and 17%) of the formula. The extrusion was conducted at predetermined temperature, feeding rate and screw speed using a twin-screw extruder. Data show that adding GP in the formula caused product darkening, decreased product expansion ratio (ER), hardness and brittleness (P<0.05). The feed moisture showed greater impacts on the ER and texture than GP content. Lower feed moisture (≤15%) resulted in crunchy product with better puffy properties at all GP level. Addition of GP increased total dietary fiber and polyphenol contents in dose-dependent manner (P<0.0001) and reduced in vitro starch digestibility of extrudate (P<0.05). Therefore, GP has great potential to serve as DF and polyphenol source in extrusion cooking, but the extrusion parameter such as GP content and moisture must be well controlled to minimize the undesirable effect of GP on product.