Current Trends in Gluten-Free Biscuit Formulation Using Rice Flour Enriched with Chestnut Flour and Fruit Powders

In response to the increasing consumer demand for healthier diets and the needs of individuals with gluten intolerance, chestnut flour (CF) emerges as a valuable unconventional ingredient for sustainable and functional nutrition. This study evaluated the nutritional, phytochemical, and functional properties of gluten-free biscuits formulated with whole rice flour (RF), CF, and their mixtures, where RF was replaced by CF at 0% (control), 10%, 30%, 70%, 90%, and 100% (<i>w</i>/<i>w</i>). In addition, in the 50% CF formulation, 5% of RF was substituted with fruit powders rich in phenolic compounds and recognized as fortifying agents, such as chokeberry (CP), açaí (AP), and blueberry (BP). Proximate composition, macro- and microelement content, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (DPPH and FRAP assays) were determined for the individual flours, composite flours, fruit powders, and biscuit formulations. Structural characteristics were assessed using Small- and Wide-Angle X-ray Scattering (SAXS/WAXS) analysis and Fourier Transform Infrared Spectroscopy (FTIR). Results showed that CF incorporation enhanced both the nutritional and functional profile of flours and biscuits, increasing protein, fiber, lipid, and mineral contents while reducing carbohydrates, and improving TPC, TFC, DPPH, and FRAP values. Fortification with 5% CP, AP, or BP further boosted the phytochemical content of the biscuits, with the chokeberry-enriched sample exhibiting the highest TPC (348.88 mg GAE/100 g d.s.), TFC (253.82 mg QE/100 g d.s.), DPPH (50.36%), and FRAP (21.07 μM Fe²⁺/g d.s.). The combination of 50% CF and 5% CP provided dual benefits, significant bioactive enrichment alongside the preservation of desirable technological properties. Complementary SAXS/WAXS and FTIR analyses indicated that CF and fruit powders enhanced molecular interactions and matrix cohesion, which may contribute to improved texture and antioxidant potential of the biscuits. Overall, this formulation offers a promising and practical approach to developing functional gluten-free biscuits with enhanced nutritional, phytochemical, functional, and structural characteristics.