From agricultural waste to antioxidant-rich extracts: Green techniques in extraction of polyphenols from sugar beet leaves

Different conventional and “green” extraction techniques (solid/liquid extraction, microwave and ultrasound assisted extraction, pressurized liquid extraction and subcritical water extraction) were tested using different operating conditions in the recovery of valuable polyphenol compounds from sugar beet leaves. All tested extraction techniques provided considerable extraction yield in the range from 18.21% to 37.04%. Total phenolic content ranged from 0.4504 up to 1.7171 (g GAE/100 g DW) with the highest values obtained by using microwave and ultrasound assisted extraction. Extraction parameters had highly significant effect on the concentration of bioactive compounds recovered by pressurized liquid extraction and subcritical water extraction. Individual phenolic profile of sugar beet leaves extracts largely depended on the applied extraction technique, however, vitexin was the most abundant phenolic compound present in all extracts regardless of the extraction technique. Investigation of extracts antioxidant activity through DPPH, FRAP and ABTS values indicated the lowest antioxidant activity of extracts obtained by solid/liquid extraction compared to other extraction techniques. • Utilization of sugar beet leaves for recovery of antioxidant polyphenols. • Evaluation of conventional versus novel extraction techniques for efficient valorization. • Emerging extraction techniques provided improvements in extracts bioactive significance. • The major phenolic acids and flavonoids were determined by HPLC. • Efficient valorization of agricultural waste to valuable bioactive compounds was achieved.