Citrus Peel Flours: From Residues to Bioactive Ingredients for Food Applications

The high consumption of citrus fruits generates large amounts of peel bioresidues, whose valorization represents an important strategy for sustainable agri-food systems. This study aimed to characterize the nutritional, chemical, and bioactive properties of flours obtained from orange (FL), tangerine (FT), lime (FLA), and lemon (FLO) peels, and to evaluate their potential as functional food ingredients. The flours were evaluated for proximate composition, organic acids, phenolic compounds, fatty acids, free sugars, and bioactive properties. Lime flour showed the highest protein, ash, dietary fiber, and total phenolic contents, with hesperidin identified as the predominant compound. The corresponding extracts exhibited relevant antioxidant, antimicrobial, antiproliferative, and nitric oxide (NO) production inhibitory activities, with lime flour presenting the strongest overall bioactive potential. Based on these results, lime flour was selected for application in a food model by partially replacing wheat flour (10% and 20%) in "Madalenas", a traditional Portuguese muffin cake. The incorporation of lime flour improved product preservation compared with the control formulation and samples containing a synthetic preservative (potassium sorbate). These findings highlight the potential of citrus peel flours, particularly lime flour, as natural functional ingredients and sustainable alternatives for food formulations, contributing to waste valorization and circular economy approaches in the agri-food sector.