Valorisation of baobab (Adansonia digitata) seeds by ultrasound assisted extraction of polyphenolics. Optimisation and comparison with conventional methods

Abstract

In this study, ultrasound-assisted extraction (UAE) of phenolic compounds in baobab (Adansonia digitata) seeds was optimised using RSM. Based on the single factor experiment results, the effect of four parameters, extraction time (10–20 min), temperature (40–60 °C), % amplitude (30–50) and solvent to solid ratio (20–30, mL/g) on Total Flavonoids Content (TFC) were investigated and optimised using a central composite design (CCD). The predicted optimal conditions with the highest desirably (0.874) were: 20 min, 30% amplitude, 60 °C temperature and 30 mL/g solvent to solid ratio. Under these conditions, the experimental TFC value (1633.84 ± 10.75 mg RE/100 g DW) was highly correlated with the predicted value (1631.77 mg RE/100 g DW). Moreover, a comparative study confirmed that the recovery of TFC, TPC and antioxidant activity (DPPH and FRAP) was significantly higher in UAE than maceration and Heat Assisted Extraction (HAE) extraction methods in addition to a shorter extraction time. HPLC analysis of the UAE optimised sample extract revealed the presence of 10 phenolic compounds with the highest concentration of D-(+) catechin (87.18 ± 14.57 µg/g). This study is the first attempt to optimise UAE parameters for the extraction of phenolic compounds in baobab seeds.