Miracle Fruit Leaf Extract: Antioxidant Activity Evaluation, Constituent Identification, and Medical Applications

Abstract

A systematic study was carried out on the antioxidants in miracle fruit leaf extract. The total phenols, total flavonoids, saponins and the antioxidant activities of the extract were evaluated using the 2,2′-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis-3-ethyl-benzotiazolin-6-sulfonic acid (ABTS), metal chelating capacity (MCC) and ferric reducing antioxidant power (FRAP) assays. The results showed that the leaves contained high phenol concentrations of 90.0 ± 4.78 mg gallic acid equivalent/g dry weight, total flavonoids at 33.0 ± 1.92 mg rutin equivalent/g dry weight, and saponins at 27.8 ± 1.64 mg oleanolic acid equivalent/g dry weight. The extract possessed excellent free radical scavenging ability and high antioxidant capacities. Furthermore, eighteen polyphenol and flavonoid constituents in the extract were identified by using ultra-high performance liquid chromatography-diode array detector-tandem mass spectrometry (UPLC-DAD-MSn) method and standard chemicals. The constituents were gallic acid, 5-O-caffeoylquinic acid, 3-O-p-coumaroylquinic acid, 5-O-p-coumaroylquinic acid, 3-O-feruloylquinic acid, 4-O-caffeoylquinic acid, 4-O-p-coumaroylquinic acid dimer, 4-O-p-coumaroylquinic acid, 4-O-feruloylquinic acid, 4-O-feruloylquinic acid, rutin, myricetin-3-O-rhamnoside, quercetin-3-D-galactoside, quercetin-3-glucoside, kaempferol-3-O-glucoside, quercetin-3-rhamnoside, myricetin-O-galloylrhamnoside and quercetin-3-O-(2′′-galloyl)-rhamnoside.Eight constituents were quantified with values from 0.12 to 4.13 mg·g^‒1. The extract of miracle fruit leaves was also used in an anti-Alzheimer's disease model for potential medical applications. The assay indicated that the extract provided apparent inhibition for the paralysis of Caenorhabditis elegans at a concentration of 0.02 mg·mL^‒1. This work demonstrated that miracle fruit leaves are rich in bioactive antioxidants with potential for drug and functional product development.

Keywords:

• Antioxidant activity
• miracle fruit leaves
• paralysis assay
• polyphenols
• ultra-high performance liquid chromatography-diode array detector-tandem mass spectrometry (UPLC-DAD-MSn)

Disclosure statement

The authors declare that they have no conflicts of interest.

Additional information

Funding

This work is supported by the National Natural Science Foundation of China (No. 21505155), and the financial supports by the Fund on Basic Scientific Research Project of Nonprofit Central Research Institutions (Nos. 1630062017034, 1630062018003). The author at Guizhou Medical University acknowledges the support from the Science and Technology Bureau, Guiyang Municipal Government, China under grant [2017]30-27.