Ginkgo biloba preparations from leaves are widely used for the treatment of mild cognitive dysfunctions. This work compared thirteen commercial dietary supplements with fresh G. biloba leaves. Anticholinesterase activities and the levels of total phenolics were studied using corresponding spectrophotometric methods. Antioxidant activities were tested using ABTS and DPPH free radicals. Phenolic acids and quercetin contents were determined using HPLC-DAD. G. biloba preparations more effectively inhibited the activity of butyrylcholinesterase than acetylcholinesterase with significant (p < 0.05) differences between preparations. Selected preparations had both the highest content of total phenolics and the antioxidant activity (with ABTS and/or DPPH) whereas in the case of other samples, adverse results were obtained. Significant (p < 0.05) differences in the quercetin content were seen between individual preparations. Gallic, protocatechuic, syringic, 4-OH-benzoic, chlorogenic, caffeic, sinapic, ferulic, 4-OH-cinnamic and o-coumaric acids were detected in studied samples. The preliminary characterization of acetyl- and butyrylcholinesterase inhibitors from G. biloba with Sep-Pak C18 and polyvinylpolypyrrolidone revealed that these compounds are phenolics, although non-phenolics exhibiting the inhibitory activity were present in the leaves. The study aiming the purification of cholinesterase inhibitors from G. biloba is in progress.

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