Green extraction of phenolics and flavonoids from black mulberry fruit using natural deep eutectic solvents: optimization and surface morphology

Abstract

Abstract This study deployed ultrasonic-assisted extraction (UAE), combined with natural deep eutectic solvents (NADES), to extract phenolics and flavonoids from the black mulberry fruit, and the antioxidant activity was examined. The extraction yields of NADES-based UAE were assessed based on total phenolic and flavonoid contents (TPC and TFC, respectively). NADES produced from choline chloride-lactic acid at a 1:2 molar ratio had the highest extraction yield. One-factor experiments evaluated the effect of UAE conditions (liquid-to-solid ratio, water content in NADES, temperature, and time) on TPC, TFC, and antioxidant activity. Response surface methodology with the Box-Behnken design model optimized the NADES-based UAE process based on response (TPC, TFC, ABTS, OH, and DPPH). The optimal conditions for the NADES-based UAE process were 70 ml/g of LSR, 38.9% water content in NADES, 67.9°C, and 24.2 min of retention time. The predicted values of the Box-Behnken design were compatible with the experimental results. Moreover, scanning electron microscopy was used to survey the surface of black mulberry fruit with and without sonication. This study proposes an efficient and green method for extracting bioactive compounds from black mulberry fruits.