Methodology optimization for the analysis of phenolic compounds in chestnut (Castanea sativa Mill.)

In vitro antioxidant and antibacterial activities with polyphenolic profiling of wild cherry, the European larch and sweet chestnut tree bark

This study is a comparative investigation of antioxidant and antibacterial properties of tree bark extracts of three common European species, Prunus avium L., Larix decidua Mill. and Castanea sativa Mill. The bioactive compounds present in the bark were recovered in 80% aqueous ethanol using ultrasound as the green extraction method. The antioxidant potential of the extracts was assessed with multiple biochemical assays: total phenol content (TPC) expressed in gallic acid equivalent (GAE), 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) expressed in trolox equivalent (TE), and ferric reducing ability of plasma (FRAP) expressed in ascorbic acid equivalent (AAE). Sweet chestnut bark extract showed the highest antioxidant activity with TPC of 174.25 ± 16.95 mg GAE/g dry weight, DPPH (IC50) of 2.69 ± 0.03 μg/mL, ABTS of 739.65 ± 24.41 mg TE/g dry weight and FRAP of 207.49 ± 3.62 mg AAE/g dry weight. The antibacterial activity of the extracts was evaluated by disk diffusion test, minimal inhibitory concentration (MIC) assay and bacterial growth curves. Sweet chestnut bark extract gave IC50 values of 0.25 mg/mL and 1.00 mg/mL against E. coli and S. aureus, respectively. The polyphenolic profiling of the bark extracts was performed to identify the major compounds responsible for the bioactivities using high-performance liquid chromatography/tandem mass spectrometry (HPLC–MS/MS). The bark extracts were rich in natural antioxidants, thus holding tremendous potential for use as natural additives in food industry.

Graphic abstract

Subcritical Water Extraction of Chestnut Bark and Optimization of Process Parameters

The aim of the work was the optimization of the subcritical water extraction process of chestnut bark using Box–Behnken response surface methodology. The influence of process parameters, such as temperature, extraction time and solvent-solid ratio, on extraction yield, yield of the main compounds, total phenol content, total tannin content and antioxidant activity has been investigated. The identified compounds were ellagic and gallic acids, ellagitannins (vescalagin, castalagin, 1-o-galloyl castalagin, vescalin and castalin), sugars (maltose, glucose, fructose and arabinose) and sugar derivatives (5-HMF, furfural and levulinic acid). Finally, the optimal process conditions for obtaining the bark extract highly rich in ellagic acid and with satisfactory levels of total phenols and total tannins have been determined.