Sustainable valorization of fruit waste: Extraction, characterization, and application of pectin in jam

In this study, we aimed to extract and evaluate pectin from apple (Malus domestica), lemon (Citrus limon), and lime (Citrus aurantiifolia) peels using microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE) techniques with different extractants. The effects of microwave power and irradiation time on pectin yield were investigated in MAE. The impacts of temperature and sonication time were assessed for UAE. The extracted pectin was subsequently used to prepare java plum (Syzygium cumini L.) jam. The highest pectin yield (18.25%) was obtained from lime peel using MAE at 500 W for 3 minutes, while UAE yielded 11.1% from lemon peel at 65 ℃ for 45 minutes. The extracted pectin was characterized as high-methoxy pectin, with a degree of esterification ranging from 50.13% to 61.63%. Fourier transform infrared spectroscopy confirmed its structure, showing a peak at 1700–1770 cm-1 for polygalacturonic acid and characteristic fingerprints in the 1600–1750 cm-1 region. Scanning electron microscopy revealed that UAE-derived apple peel pectin had a ruptured surface, whereas MAE-derived lime peel pectin exhibited a porous structure, indicating a higher degree of hydrolysis. Jams prepared with the pectin showed total soluble solids of 65.1°, 67.2°, and 68.1° Brix for apple pectin jam (APJ), lemon pectin jam (LPJ-a), and lime pectin jam (LPJ-b), respectively. The LPJ-b exhibited the highest viscosity (75.1 cP) and received the best sensory acceptability score. MAE was more effective than UAE, providing a higher yield in a shorter time. Furthermore, the jam formulated with MAE-extracted lime pectin demonstrated superior physicochemical and organoleptic properties.