Polyphenol Content and Antioxidant Potential of Rhubarb <i>(Rheum Rhabarbarum)</i> STEM By-products Depending on Solvent Polarity and Extraction Technique

The aim of the study is to evaluate the effect of solvent polarity and extraction technique on the recovery of antioxidants from rhubarb (Rheum rhabarbarum) by-products with single-step – maceration, and ultrasound assisted extraction, and two-step extraction methods - Soxhlet extraction with ethyl acetate, followed by repeated extraction of the residues. Extracts obtained using ethanol showed the highest extract yield, the highest total phenolic content ( 78.6 ± 2.4 μ g m L − 1 ) , and exhibited high antiradical scavenging activity (DPPH method), the total flavonoid content ( A l C l 3 m e t h o d ) was up to 4.8 ± 0.2 μ g m L − 1 . NMR analyses showed that the spectra of non-polar extracts showed the presence of various aliphatic compounds. Findings suggest a sustainable use of rhubarb residues, contributing to waste reduction while exploiting their bioactive potential in cosmetics, pharmaceuticals, and food products due to their strong antioxidant activity.