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This paper presents the influence of spruce bark (Picea abies) particle size and size distribution on the separation of polyphenols, using a green extraction process (ultrasound-assisted extraction – UAE), in order to highlight the kinetic mechanism. Experiments were performed at 50 °C, for 45 minutes, using ethanol-water (70% v/v) as solvent. The considered particle size fractions were: 0.25, 0.315, 0.4, 0.5, 0.63 and 1 mm. The crude extracts were assessed using the Folin Ciocalteu method for total polyphenols content (TPC) and high-performance thin layer chromatography (HPTLC) for identifying simple phenolic acids and tannins. The study points out that particle size significantly influences the UAE process in terms of separated polyphenols and kinetic mechanism as well. From the particles with the lowest size, the highest amounts of simple phenolic acids (sinapic acid, p-coumaric acid) and tannins (catechin) were obtained. Extraction kinetics was estimated using a second order model. Results showed a good prediction of this model for the extraction kinetics in all the experiments (R 2 > 0.911), which gave the possibility to estimate the concentration of polyphenols at saturation (Cs), the rate constant (k) and the initial rate (h). All these parameters were affected by the particle size and size distribution of spruce bark.

INFLUENCE OF PARTICLE SIZE AND SIZE DISTRIBUTION ON KINETIC MECHANISM OF SPRUCE BARK POLYPHENOLS EXTRACTION