Substitution of Wheat Flour by Extrudate Orange Peel Dietary Fiber Concentrate in Biscuits: Changes in Mixolab Thermomechanical Behavior, Flour Technofunctionality, and Water Sorption Isotherm Properties

Applicability of dietary fiber concentrates (DFCs) from fruit byproducts in food formulations is limited by the high proportion of insoluble dietary fiber (IDF) and its negative effect on sensory and functional quality. Extrusion modifies dietary fiber composition, impacting technological and physiological functionalities. This research evaluated the effect of wheat flour substitution by unprocessed or extruded orange peel DFC (0%-20%) on the properties of biscuits. Composition, Mixolab analysis, dough extensibility, and solvent retention capacity of composite flours were determined. Proximal composition, sensory acceptance, firmness, and water sorption isotherms of biscuits were evaluated, and Brunauer-Emmet-Teller (BET) equation parameters were estimated. Soluble dietary fiber (SDF) and IDF ratio increased with extrusion from 0.15 to 0.98 (w/w). Extruded DFC 5% and 10% substitution had the least detrimental effect on Mixolab profile, extensibility, and solvent retention capacity. The use of unprocessed orange peel decreased technological characteristics. Proximal composition and sensory acceptance had no statistical difference. Extruded DFC increased the high molecular weight SDF content in biscuits. Textural shelf-life of biscuits showed that extruded DFC at 10% substitution generates a biscuit with similar initial hardness with less change during 10 days of storage. Water adsorption isotherms of biscuits with orange peel DFCs showed a direct increase in values according to the substitution in wheat flour. The BET model had a good fitting to describe the adsorption experimental data. The increase in DFC content in the biscuits favored the moisture retention capacity throughout the <i>aw</i> range of the isotherms. Extruded orange peel DFC could be used to reduce wheat flour used in biscuit formulations without compromising dough machinability and textural quality, with a positive nutraceutical effect due to the increase in TDF, specifically high-weight soluble dietary fiber.