Ultrasonic-assisted extraction and thermal stability of phytochemicals from fenugreek leaves

The current investigation aimed to determine the optimum ultrasonic-assisted extraction conditions of the phytochemicals from fenugreek leaves (Trigonella-foenum graecum L.). The effects of the solvent type, sample–solvent ratio, amplitude and extraction time on total phenolic compounds, total flavonoids, antioxidant activity and total saponin content were studied with a multi-objective perspective. Quadratic models were obtained by desirability function approach and a numerical optimization study was carried out to achieve the highest amount of phytochemicals in the extracts. Further, thermal stability of the extracts produced at the optimum conditions was determined in terms of the amount of the phytochemicals at different pH values (pH 3.0–9.0). The optimum extraction conditions of the ultrasonic-assisted extraction process were 100% of water, 35.02 g/L of sample–solvent ratio, 52.63% of amplitude, and 61.73 min of extraction time. Thermal stability of the extract obtained at the optimum extraction conditions was higher at pH 3.0 than that of pH 6.0 and pH 9.0, and its antioxidant properties were preserved by ~25% even after 10 h at 60 °C. •Fenugreek leaf extracts were rich in antioxidant activity.•Ultrasonic-assisted extraction was optimized using response surface methodology.•Water was the best solvent for the extraction process.•Thermal stability of the extracts was higher at pH 3.0.•Fenugreek leaf extract has potential to be use as a natural antioxidant.