Abstract:

This study aimed to investigate the effects of solvents with different polarities on the extraction of phenolic
compounds from sweet potato leaves, to compare antioxidant activities of the extracts, and to identify the main antioxidants
of the extract with the highest antioxidant activity. Seven solvents, namely distilled water, methanol, ethanol, acetone,
n-butanol, ethyl acetate and chloroform, were used to extract polyphenols from sweet potato leaves. The contents of total
phenolics, total flavonoids and anthocyanins, as well as in vitro antioxidant activities of these extracts were compared.
The major antioxidant compounds in the extract with the highest antioxidant activity were identified by high performance
liquid chromatography tandem mass spectroscopy (HPLC-MS/MS). Results indicated that solvent polarity had a
substantial influence on the extraction efficiency of polyphenols from sweet potato leaves and the antioxidant activities
of the extracts. The water extract had the highest crude extract yield of (37.13 ± 1.60)%, but the highest total phenolic
content (13.80 mg GAE/g) and total flavonoid content ((5.68 ± 0.35) mg QE/g) were observed in the methanol extract and
it exhibited the strongest DPPH (1,1-diphenyl-2-picryl-hydrazyl-hydrate) radical scavenging activity with IC50 value of
0.32 mg/mL and reducing power of ρ0.5 value of 0.95 mg/mL. A total of 9 phenolic compounds, namely caffeic acid,
chlorogenic acid, 3,4-dicaffeoylquinic acid, 3,5-dicaffeoylquinic acid, 4,5-dicaffeoylquinic acid and 3,4,5-tricaffeoylquinic
acid, were identified from the methanol extract, including 3 phenolic compounds.

Key words: sweet potato leaves, polyphenols, solvent extraction, antioxidant activities, HPLC-MS/MS