Multifunctional Citrus Peel Pectins from Seven Species: A Comparative Study of Physicochemical, Techno-Functional, and Bioactive Properties

Citrus peel, a major by-product of citrus processing, is a rich source of pectin and other bioactive compounds. In this study, pectin extracted from seven citrus species was comprehensively characterized for its structural, spectral, thermal, physicochemical, techno-functional, antioxidant, and anti-amylase properties. The extracted pectin (~50% methyl esterification) contained residual cellulose, hemicellulose, lignin, and proteins, with Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-Vis) confirming typical galacturonic acid-based structures. Fluorescence analysis revealed emission shifts (420–500 nm) compared to standard pectin. Thermal analysis indicated multi-stage degradation, with major transitions linked to moisture loss, polysaccharide depolymerization, and lignin oxidation. X-ray diffraction (XRD) confirmed a predominantly amorphous structure with minor cellulose domains. The pectin solution showed negative zeta potential, shear-thinning behavior, and high conductivity. Functionally, it exhibited strong swelling, hygroscopicity, and water/oil holding capacity, but low foaming ability. Biologically, it demonstrated moderate antioxidant activity and α-amylase inhibition. These findings highlight citrus pectin as a promising sustainable ingredient for food and pharmaceutical applications, with future work needed to enhance its solubility and bioactivity.