Effect of extraction conditions and techniques on the antioxidant properties of ginger cultivated in Poland

Ginger cultivated under temperate climatic conditions may differ in its phytochemical composition and antioxidant potential from ginger grown in tropical regions; however, systematic data remain scarce. This study quantitatively compared two extraction methods: conventional solid-liquid extraction (CE) and ultrasound-assisted extraction (UAE) for isolating bioactive compounds from the rhizomes and leaves of ginger cultivated in Poland and evaluated the antioxidant activity of the resulting extracts. A full factorial Design of Experiments (3²) was applied to optimize the effects of ethanol concentration (50–100%) and extraction temperature (25–45 °C). Ethanol concentration was identified as the key factor influencing total phenolic content, the extraction efficiency of 6-gingerol and 6-shogaol, and antioxidant activity. UAE consistently outperformed CE, particularly for rhizome extracts. Under optimal UAE conditions (45 °C, 100% EtOH), rhizome extracts contained 79.87 mg/g dw of 6-gingerol and 17.71 mg/g dw of 6-shogaol, exhibiting strong antioxidant activity (DPPH IC50 = 0.68 mg/mL; FRAP EC0.5 = 0.22 mg/mL). In comparison, optimal CE conditions (45 °C, 50% EtOH) yielded lower concentrations (53.1 mg/g dw of 6-gingerol and 14.19 mg/g dw of 6-shogaol), with slightly reduced antioxidant performance (DPPH IC50 = 0.71 mg/mL; FRAP EC0.5 = 0.16 mg/mL). Leaf extracts contained significantly lower levels of active compounds and demonstrated markedly weaker antioxidant activity across both extraction methods. This study is the first to systematically optimize and directly compare CE and UAE using a DoE approach for both rhizomes and leaves of ginger cultivated in a temperate European climate, demonstrating that locally grown ginger rhizomes remain a valuable source of bioactive compounds suitable for functional foods, nutraceuticals, and dietary supplements.