Ultrasound-assisted ionic-liquid extraction of hawthorn pectins: Structural features, rheological behavior, and...

Ultrasound-assisted extraction (UAE) combined with ionic liquids (ILs) has been increasingly applied for pectin recovery by promoting cell-wall disintegration and polysaccharide release under mild conditions. However, limited information is available on the structural and network-related characteristics of hawthorn pectin fractions obtained under different ultrasound-assisted ionic-liquid extraction windows. In this study, hawthorn pectins were extracted using ultrasound-assisted extraction (UAE) with four ionic liquids: [Bmim]Cl, [Emim][Ac], [Amim]Cl, and [Bmim][HSO₄], with aqueous UAE used as the control. All samples were homogalacturonan-dominated low-methoxyl pectins (galacturonic acid (GalA) ≥ 74.1%, degree of esterification (DE) ≤ 43.0%). Specifically, the [Amim]Cl-extracted pectin achieved the highest yield (7.93%), whereas BH-HP showed the highest weight-average molecular weight (Mw, 856.36 kDa) and peak temperature (274.16 °C). In contrast, [Emim][Ac] yielded pectin with the lowest DE (25.03%) and smallest hydrodynamic size. All samples showed pronounced shear-thinning behavior, but differed in viscoelastic balance and temperature responsiveness, indicating distinct aggregation and network-related characteristics after redispersion in water. In addition, the CK-HP/[Bmim][HSO₄] system showed concentration-dependent spectral and rheological changes along with inversion-resistant gel-like behavior, suggesting preliminary gel-like network formation in this ionic-liquid medium. These findings indicate that IL-specific optimized UAE extraction windows generated hawthorn pectin fractions with distinct structural and colloidal/network-related behaviors, providing a basis for application-oriented formulation design.