Ultrasound Assisted Pectin Extraction from Persimmon Pomace: Yield and Quality Characteristics

Abstract

Persimmon pomace, an abundant by-product generated during fruit processing, represents a promising yet underutilized source of pectin and carotenoids. In this study, pectin and carotenoids were extracted from persimmon (Diospyros kaki L.) pomace, and the influence of ultrasound-assisted extraction on pectin yield and physicochemical properties was systematically evaluated. A full factorial experimental design was employed to investigate the effects of temperature (50–60 °C), pH (1.5–2.0), extraction time (30–45 min), acid type (citric and nitric acids), and extraction method (conventional vs. ultrasound-assisted). All process variables significantly affected pectin yield (p < 0.001), with ultrasound-assisted extraction exhibiting the strongest positive effect. Among the tested conditions, the combination of ultrasound treatment and nitric acid resulted in the highest pectin yield, highlighting a significant interaction between extraction method and acid type. Ultrasound treatment significantly enhanced pectin yield, equivalent weight, methoxyl content, and degree of esterification, while maintaining acceptable anhydrouronic acid content (>63%), indicating good purity and functional quality. Notably, the degree of esterification increased from low- to high-methoxyl range following ultrasound treatment, expanding the potential applications of the extracted pectin. In addition, ultrasound-assisted extraction improved carotenoid recovery from persimmon pomace, with total carotenoid content ranging from 2.78 to 3.26 µg g⁻¹. Overall, the results demonstrate that ultrasound-assisted extraction is an efficient and sustainable approach for enhancing the recovery and functionality of pectin and carotenoids from persimmon pomace.