Chemical Composition of Black Spruce (Picea mariana) Bark Extracts and Their Potential as Natural Disinfectant

Abstract

The valorization of residual forest biomass from sawmills is an economic and ecological opportunity in Québec. With specialized metabolites and biological activities, several residues from Québec's tree species could have commercial potential. This study aims to study the antimicrobial efficacy of extracts from bark residues to determine their potential as a natural disinfectant. We first performed a quantification of phenolic metabolites by colorimetric tests which showed higher flavonoids and proanthocyanidins content (>27.88 mmol catechin equivalents (CE)/100 g of bark extract and >3.90 mmol CE/100g of bark extract respectively) in black spruce extracts compared to balsam fir, quaking aspen and white birch. Extraction with water (WE) followed by fractionation with ethyl acetate yielded a fraction enriched with oligomeric proanthocyanidins (OPF). WE and OPF antimicrobial activity on Escherichia coli using the broth microdilution and the dilution-neutralization methods (AOAC 960.09) demonstrated an increased antimicrobial potency with OPF. A minimal inhibitory concentration and a minimum bactericidal concentration of 0.83 mg/mL and 4.44 mg/mL respectively as well as a microbial reduction of 4.83 log CFU/mL (3% w/w with 10 min contact) and ≥5.09 log CFU/mL (1.5% w/w with 120 min contact time) were obtained. Compounds characterization using UPLC-QTOF-MS allowed to putatively identify nine antimicrobial compounds in the OPF. Taxifolin, dihydroxykampferol and andrographolide seemed to be associated with the increase of the antimicrobial activity of this fraction.