Direct vs indirect ultrasound-assisted extraction of phenolics from wild sumac (Rhus tripartita): Optimization by Response Surface Methodology (RSM) and LC-MS profiling

Abstract

This study explores the potential of wild sumac (Rhus tripartita) fruits as a rich source of antioxidants. To achieve this, two ultrasound-assisted extraction (UAE) techniques—indirect (IUAE) and direct (DUAE)—were employed under predefined conditions to optimize antioxidant recovery. The extraction parameters for each method were investigated using response surface methodology (RSM) and Box-Behnken Design (BBD), focusing on three key factors for each method. The total phenolic content, quantified by the Folin-Ciocalteu method (TP-FC), was defined as the response variable. TP-FC values ranged from ∼ 6 to ∼ 12 mg GA eq./g DW for IUAE, and from 11 to 30 mg GA eq./g DW for DUAE. Quadratic models were developed and the determination coefficients exceeded 0.9 for both methods, confirming models’ reliability. ANOVA results indicated that temperature and time were the most influential factors in IUAE, while power and time were most impactful in DUAE. Overall, DUAE proved more efficiency than IUAE, yielding up to 26.74 mg GA eq./g DW under optimal conditions (53 %, 30 min, and 80 for power, time, and liquid/solid ratio, respectively). Furthermore, the DUAE obtained R. tripartita extract was profiled for its phenolic composition. LC-MS was used for initial identification of major phenolic compounds, followed by HPLC quantification using corresponding standards. Ten compounds were unequivocally identified. Notably, masazinoflavanone, first identified in 2005, was systematically quantified for the first time in R. tripartita, emerging as the predominant compound at 36.6 mg/g DW, which accounted for 82 % of total phenolics. Other identified compounds included more common molecules, like amentoflavone, myricetin, and quercetin derivatives, with contents ranging from 0.21 and 3.47 mg/g DW.