Applied Science and Engineering Progress
Steam Explosion Extraction of Pectin from Watermelon Rinds: Identification of Integrated Crystalline Mineral Phases and Thermal Characterization
Abstract
This study explores the potential of utilizing watermelon rinds, a significant agricultural byproduct, as a sustainable source for pectin extraction using the steam explosion (SE) technique at 121 °C for 30 min. The SE-extracted watermelon pectin (WP) was characterized and compared with standard commercial citrus pectin (CP). The WP exhibited an extraction yield of 3.41 ± 0.13%, a degree of esterification (DE) of 37.42 ± 1.92%, and a methoxyl content of 6.10 ± 0.20%, classifying it as a low-methoxyl pectin. FTIR analysis confirmed the preservation of characteristic pectin functional groups. Notably, XRD patterns revealed that while CP was predominantly amorphous, WP contained co-extracted crystalline mineral phases. SEM-EDS and high-resolution elemental mapping verified that these phases, consisting of Sylvite (KCl), Calcite (CaCO3), and Halite (NaCl), were homogeneously integrated and securely embedded throughout the pectin biopolymer matrix. These findings were consistent with the significantly higher ash content (6.42 ± 0.15%) and thermal residue (43.83% at 550 °C) observed in WP than in CP. DSC analysis indicated distinct thermal phase transitions, characterized by a major endothermic dehydration peak at 135.85 °C. SEM observations confirmed that SE effectively disrupted the cell wall matrix, yielding a porous pectin network with integrated mineral microparticles. These results demonstrate that steam explosion is a promising alternative that is potentially greener than conventional acid extraction due to reduced chemical and acid consumption for producing functional pectin with co-extracted and integrated crystalline mineral phases, offering viable potential for application in functional food systems.
Keywords
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DOI: 10.14416/j.asep.2026.08.018
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