Physical properties and FTIR analysis of rice-oat flour and maize-oat flour based extruded food products containing olive pomace

•Olive pomace was successfully incorporated into extruded snack products.•The extruded snacks were enriched with dietary fiber and polyphenols.•FTIR helped to understand process induced changes to major components in formulation.•The choice of base material for extrusion has influence on final product characteristics.

Olive pomace, a waste stream from olive oil processing, was fractionated by centrifugation to obtain a supernatant and a flesh-enriched fraction, and freeze dried to obtain a powder. The dried supernatant contained 5.8% moisture, 4.8% protein, 3.5% fat, 3.5% ash, 82.4% carbohydrate (including 17.2% dietary fiber) and polyphenols (2970 mg gallic acid equivalents (GAE)/100 g). The dried flesh-enriched fraction, contained 5.9% moisture, 13.4% protein, 14.2% fat, 3.5% ash, 63.1% carbohydrate (including 42.7% dietary fiber) and polyphenols (1960 mg GAE/100 g). The extruded products using rice-oat flour or maize-oat flour mixtures as the base were formulated to contain 5% or 10% olive pomace fractions (dry basis). The extruded products with added olive pomace fractions has higher fiber (2-7 g/100 g) and polyphenol contents (67-161 mg GAE/100 g) compared to the corresponding mixtures of rice-oat flour base (0.92 g/100 g fiber, 20 mg GAE/100 g) or maize-oat flour base (3.2 g/100 g fiber, 20 mg GAE/100 g) without olive pomace fractions. Addition of olive pomace fractions reduced the die pressure and specific mechanical energy during extrusion and resulted in lower radial expansion in the extruded product. The impact of the addition of olive pomace fraction on physical characteristics of the extruded product is higher for rice-oat flour base than maize-oat flour base. The underlining mechanism was explained by FTIR analysis. FTIR showed that there were significant changes in the carbohydrate components and the structure of the proteins on extrusion, with consequent effects on the expansion and density of the extruded product. This study showed the feasibility of preparing fiber and polyphenol enriched extruded products by incorporation of olive pomace. This shows the potential of recovery and diversion of edible components from waste streams of olive oil processing for formulation of extruded products.

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