Enriching croissants with orange peel by-product powder: Impact on FTIR fingerprint and bioactive quality

Citrus fruits are among the most widely cultivated crops, with sweet orange accounting for about 70% of global production, exceeding 67 Mt annually. Citrus consumption is associated with health benefits, including antioxidant, anti-cancer, and anti-inflammatory effects, mainly attributed to bioactive compounds such as ascorbic acid, carotenoids, and phenolics, particularly glycosylated flavanones. However, during handling and processing, more than 30% of the fruit is discarded as peel waste. This study embraced a circular economy approach to develop a functional bakery product. Croissants were formulated by replacing wheat flour with organic, unwaxed dried orange peel powder at 0% (CTRL), 2%, 3%, 4% and 5% (w/w). The resulting products were characterized using Fourier-transform infrared spectroscopy (FTIR) combined with Principal Component Analysis (PCA), total phenolic content (TPC), total antioxidant capacity (TAC) via FRAP, ABTS, and DPPH assays, and sensory analysis.

FTIR analysis of freeze-dried orange peel revealed bands corresponding to cell wall polysaccharides, while croissant spectra were dominated by signals from wheat flour and butter. PCA of the spectral data (PC-1: 92%, PC-2: 5%) clearly discriminated CTRL from enriched formulations, with inter-group variance exceeding intra-group variance, confirming compositional differences. Orange peel addition significantly enhanced the functional properties: TPC increased up to 56.1% (45.3 g GAE eq. 100 g⁻¹ dw) regarding CTRL, from the lowest concentration tested (2%), with no differences among enriched samples. The 4% enriched sample showed TAC increases of 90% (FRAP), 42.8% (ABTS), and 100% (DPPH) compared to CTRL. In all cases, taste and texture remained acceptable and well-received by consumers, supporting the incorporation of orange peel as a viable alternative. These findings demonstrate chemical composition changes and antioxidant enrichment of a butter-rich, easily oxidizable bakery product, highlighting a viable, economically and health-advantageous strategy for the valorization of bioactive secondary metabolites derived from a waste product generated in millions of tons annually.