Comparative extraction of antioxidant proteins from whole frogs (<i>Rana ridibunda</i> Pollas)

The forest frog (<i>Rana ridibunda</i> Pollas) is a traditional medicinal source rich in active protein compounds. In order to extract these compounds, six extraction methods were employed, including freeze-thaw and stirring techniques. Three different solvents were utilized in this process: 0.15 M sodium chloride (NaCl), 0.05 M phosphate buffer (PB), and 0.05 M phosphate-buffered saline (PBS). The objective was to identify the most effective extraction method. The extraction efficiencies, protein content, structure, and physicochemical properties of the extracts were compared. Additionally, antioxidant activity and free amino acid composition were analyzed. The highest-scoring extract, denoted as M1, obtained through freeze-thaw extraction using 0.15 M NaCl, exhibited an extraction rate of 7.79 ± 0.71% and a protein content of 60.36 ± 2.12%. M1 also showed antioxidant activity against DPPH˙, ABTS⁺˙, and ˙OH free radicals, with IC₅₀ values of 0.41, 0.41, and 0.39 mg mL^-1, respectively. The freeze-thaw extraction method utilizing 0.15 M NaCl has been identified as effective for extracting proteins from dried forest frogs, confirming their potential as a source of antioxidant proteins for scientific research and application.