Ginkgo biloba flavonoid glycosides in antimicrobial perspective with reference to extraction method

Abstract

The present study aims to investigate the effect of extraction method on the recovery of flavonoid glycosides, antimicrobials and antioxidants from Ginkgo leaves collected from six different locations in Uttarakhand, Indian Himalaya. Four extraction methods, namely maceration, reflux, shaker and soxhlet were considered, where reflux extracts showed higher antimicrobial antioxidant activity and higher content of flavonoid glycosides. The reference standards of Ginkgo flavonoid glycosides (quercetin, kaempferol and isorhamnetin) and crude extracts were tested for their antimicrobial activity against gram positive and gram negative bacteria and fungi following disc diffusion method and minimum inhibitory concentration (MIC). All the test microorganisms were observed to be inhibited significantly by Ginkgo flavonoids in plate based assays. Correlation coefficients exhibited the extent of contribution of flavonoid glycosides in antimicrobial activity and confirmed the reflux method as a potential method for extraction. Moreover, antioxidant activity as measured by DPPH assay was also found to be higher in reflux method. Significant variation (p < 0.05) in the flavonoid glycosides among the locations was also observed and sample collected from GB6 location was found to be the best for quercetin and isorhamnetin, while GB5 for kaempferol. Significant correlation (r < 0.05, r < 0.001) was obtained while developing the relationship between total flavonoid glycosides and antimicrobials. The present study, thus suggests the reflux method of extraction to be the best for maximum recovery of flavonoid glycosides with higher antioxidant and antimicrobial activities from Ginkgo extract.

Keywords: Antimicrobials; Antioxidants; Flavonoid glycosides; Ginkgo biloba; HPLC; Indian Himalaya.

Graphical abstract

Fig. 1

Representative chromatogram of Ginkgo flavonoid glycosides (A) standard compounds (B–D), maceration, reflux and soxhlet extract of Ginkgo leaves.

Fig. 2

Flavonoid glycosides (Quercetin Kaempferol and Isorhamnetin) obtained using different extraction methods.

Fig. 3

Ginkgo flavonoid glycosides with different locations (a) Maceration (b) Reflux and (c) Soxhlet, values are mean ± standard error; mean values followed by the same latter(s) in a column are not significantly different (p < 0.05) based on DMRT.

Fig. 4

(A–C) Antimicrobial activity in Ginkgo standards- Quercetin (Q), Kaempferol (K), Isorhamnetin (I), Mixture of all the three standards (MIX) and (D–F) leaf extracts with different extraction methods (Maceration: MAC, Reflux: REF, Shaker: SHA and Soxhlet: SOX) and organic solvent (c) against: Bacillus subtilis, Serratia marcescens and Fusarium oxysporum, respectively.

Fig. 5

Relationship between total flavonoid glycosides (mg/g dw) and antimicrobial activity (Zone of inhibition (ZOI = mm) in Ginkgo leaf extracts shown as linear correlation between antimicrobial activity and total flavonoid glycosides measured by B. subtilis (A), M. roseus (B), P. putida (C), S. marcescens (D), F. oxysporum (E), T. hirsuta (F).