Molecular Weight Effects on the Physicochemical and Functional Behavior of Pectin from Pomelo Peel Waste​

Pectin has great application potential, but the effect of molecular weight on its physicochemical properties remains unclear. In this study, high‑molecular‑weight pectin (HMP, 425 000 Da) and low‑molecular‑weight pectin (LMP, 186 936 Da) were prepared from pomelo peel, a major food-processing by-product, by ultrasound‑assisted extraction and enzymatic depolymerization, respectively. Comprehensive characterization revealed pronounced molecular-weight-dependent differences. SEM and AFM revealed distinct morphologies, while XPS and FTIR confirmed comparable elemental composition and characteristic functional groups for both pectin fractions. The degree of methyl esterification was 83.42% for HMP and 65.0% for LMP. XRD indicated lower local chain ordering in HMP. Furthermore, LMP showed exhibited enhanced pH-responsive surface charge behavior, displaying a more negative ζ-potential in the weakly acidic to neutral pH range (5.0–7.0), together with a smaller particle size distribution (295–458 nm) compared with HMP (458–1000 nm). Whereas, HMP exhibited higher water absorbing capacity (305.8%) than LMP (253.8%). These results demonstrate that molecular weight is a critical determinant of pectin physicochemistry, governing chain organization, surface charge behavior, hydration dynamics, and functional performance, and provide a rational framework for the valorization of citrus by-products in the design of functional pectin-based biomaterials for food, pharmaceutical, and healthcare applications.