Ultrasound‑enhanced green recovery and antioxidant potential of polyphenols from four Abelmoschus manihot bio‑wastes.

Abstract

Abelmoschus manihot (A. manihot) flowers are well studied, but its fruit, leaf, stem, and root bio-wastes remain underutilized. This study developed a green ultrasonic-assisted extraction (UAE) process using a temperature-controlled bath (40 kHz, 12 L). Calorimetric calibration established linear acoustic energy output (R2 = 0.9942), and a medium acoustic energy density of 113.6 W/L was selected. This energy density ensured stable cavitation during extraction. KI dosimetry quantified cavitation: triiodide concentration increased with power above a threshold, and time-course data were fitted by both linear and nonlinear models, confirming continuous sonochemical activity. Water, ethanol, and water/ethanol (1:1, v/v) were compared under UAE and shake-assisted extraction. Water/ethanol with UAE gave the highest polyphenol yields and antioxidant activities, with a net increment of 3.87 mg GAE g-1 for leaf. Pseudo-second-order kinetics best described extraction, and UAE increased rate constants, indicating reduced mass transfer resistance. SEM revealed ultrasound-induced cell wall disruption, more pronounced in leaf and fruit than in lignified stem and root. Extraction parameters were optimized by response surface methodology and back-propagation artificial neural network, with the latter superior. Antioxidant assays ranked fruit > leaf > stem > root. UHPLC-MS/MS metabolomics identified 508 polyphenols dominated by flavonoids (57.75 %) and phenolic acids (38.76 %), with tissue-specific accumulation. Mantel test showed flavonoids and phenolic acids strongly correlated with antioxidant activity, with tannins playing auxiliary roles. This integrated acoustic, kinetic, and microstructural evidence provides a mechanistic basis for ultrasound-enhanced polyphenol recovery. These findings demonstrate the greenness and potential of UAE for recovering polyphenols from agricultural bio-wastes.

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