The leaf sheaths of the red sorghum (Sorghum bicolor L.) Moench) are a plant waste, which has a stable red color due to the bioactive 3-deoxyanthocyanidins such as apigeninidin (APG) and luteolinidin (LUT). In the present study, a multiple optimization process was conducted on ultrasound-assisted extraction (UAE) combined with natural deep eutectic solvent (NADES) to maximize the extraction of 3-deoxyanthocyanidins from the leaf sheaths of the red sorghum. The preliminary experiments showed that the contents of APG and LUT were found in ranges of 2.25 ± 0.01-31.59 ± 0.09 mg/g and 1.36 ± 0.01-30.44 ± 0.11 mg/g, with choline chloride: acetic acid (CHAC), providing the highest values compared with choline chloride: glycerol (CHGLY), choline chloride: ethylene glycol (CHEGLY), choline chloride: lactic acid (CHLA), distilled water, methanol and ethanol. The optimization of the prominent NADES (CHAC) component based on the central composite design resulted in an increase in APG and LUT, being 39.15 ± 0.58 mg/g for APG and 37.89 ± 0.86 mg/g for LUT. The optimization of the extraction conditions using the Box-Behnken design promoted the extraction of APG and LUT, being 54.97 ± 0.96 mg/g for APG and 48.62 ± 0.44 mg/g for LUT at the optimum conditions of 29.93 min, 89.86% and 27.95 mL for extraction time, amplitude and NADES content, respectively. The antioxidant activity of 3-deoxyanthocyanidin-rich extract was found to be 1117.07 ± 21.92 µmol TE/g, 837.36 ± 16.60 mmol TE/g and 5151.03 ± 39.44 mmol ISE/g, for ABTS, DPPH and FRAP assays, respectively. CHAC extract exhibited the highest in vitro bioaccessibility, antidiabetic activity, antimicrobial activity and thermal properties compared with the aqueous extract.
Keywords: 3-deoxyanthocyanidins; Bioaccessibility; Biological activity; Natural deep eutectic solvents; Sorghum bicolor; Thermal stability.
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