Comparative profiling of fresh citrus peels: composition, functionality, and bioactive potential as sustainable food ingredients

Abstract Fresh peels from seven citrus species (Citrus aurantium, C. limetta, C. limon, C. maxima, C. reticulata, C. paradisi, and C. sinensis) were comparatively characterized to evaluate their compositional, physicochemical, nutritional, techno-functional, and bioactive properties and assess their suitability as sustainable functional food ingredients. Citrus peels were predominantly composed of structural polysaccharides, including pectin (27.5–33.0 g/100 g dw), cellulose (15.0–18.0 g/100 g dw), and hemicellulose (13.6–15.3 g/100 g dw), together with proteins (12.5–15.0 g/100 g dw), lipids (8.98–11.10 g/100 g dw), lignin, and bioactive compounds such as phenolics, flavonoids, and carotenoids. Comparative amino acid profiling revealed proline, aspartic acid, glutamic acid, serine, and glycine as the predominant amino acids, while glucogenic amino acids accounted for 77–92% of the total amino acid pool. The lipid fraction was characterized by high proportions of linoleic acid (30.6–40.8%), palmitic acid (22.5–29.1%), and oleic acid (4.8–26.8%), resulting in favorable unsaturated fatty acid profiles. Essential oil composition was dominated by limonene (58.2–92.4%), accompanied by lower proportions of oxygenated monoterpenoids, including linalool, α-terpineol, neral, and geranial. Citrus peel extracts exhibited antioxidant activity (IC50 = 280–315 μg/mL) and α-amylase inhibitory activity (IC50 = 267–295 μg/mL). The aqueous extracts displayed negative ζ-potential values (− 45 to − 58 mV), particle sizes ranging from 290 to 378 nm, and desirable techno-functional characteristics, including swelling, water-holding capacity, emulsifying activity, and shear-thinning behavior. Among the evaluated species, C. sinensis exhibited superior hydration-related properties, whereas C. paradisi showed the most favorable lipid nutritional profile. These findings demonstrate that fresh citrus peel represents a sustainable source of dietary fiber and bioactive compounds with potential applications as a functional food ingredient and nutraceutical raw material.