Appraisal of phenolic compounds, antioxidant activity and in vitro gastrointestinal digestion of borage (Echium amoenum) flowers using natural deep eutectic solvent (NADES)

Borage is used traditionally in folk medicine for centuries and is reputed in many ancient civilizations. This paper examined the effectiveness of natural deep eutectic solvent (NADES) based on choline chloride and glycerol (CHGLY) for the extraction of phenolic compounds from borage. The results showed that NADES was significantly more efficient than the traditional solvents such as water, methanol and ethanol. NADES gave the highest amounts of gallic acid (157.25 +/- 8.47 mg/kg), catechin (100.21 +/- 014 mg/kg), hydroxybenzoic acid (256.00 +/- 1.70 mg/kg), chlorogenic acid (530.91 +/- 15.85 mg/kg), caffeic acid (95.70 +/- 9.26 mg/kg), vanillic acid (600.07 +/- 6.19 mg/kg), epicatechin (175.99 +/- 10.35 mg/kg), p-coumaric acid (77.17 +/- 5.16 mg/kg) and ferulic acid (33.13 +/- 096 mg/kg). These phenolic compounds were optimized by choosing the molar ratio, water content, extraction temperature and extraction time as variables. The optimum conditions were 1:3.40 of molar ratio, 40% of water content, temperature of 75 degrees C and extraction time of 35 min. Under these conditions, the predicted and experimental values were found close, confirming the reliability of the optimization process. The NADES extract of borage exhibited great antioxidant properties giving a total phenolic content of 85.02 +/- 0.22 mg GAE/g, reducing the antioxidant power of 1505.72 +/- 21.94 mmol ISE/g, DPPH radical scavenging activity of 705.01 +/- 10.35 mmol TE/g and ABTS radical scavenging activity of 59.70 +/- 3.44 mmol TE/g. The NADES extract of borage displayed high in vitro bioavailability ranging from 18.20 +/- 1.06 to 82.99 +/- 2.51% with gallic acid and caffeic acid as the best bioavailable compounds. CHGLY was found to be an eco-friendly solvent and easy to be applied for the efficient extraction of phenolic compounds.