Comparison of the composition of Pinus radiata bark extracts obtained at bench- and pilot-scales

Pine bark represents an interesting byproduct from the forest that can be used as a source of antioxidants. To study the phenolic fraction of this matrix, Pinus radiata bark was extracted with a 75% ethanol solution at both bench- and pilot-scales followed by an analysis of the extraction yield variation, chemical composition (total phenolics content, tannins content, and phenol composition determined by RP-HPLC-DAD-MS and GPC) and antioxidant properties (free radical scavenging capacity, DPPH; reduction capacity, FRAP; chelating activity, ICA). Extractions at bench- and pilot-scales were performed at 120°C for 120min at a solid-to-liquid ratio of 1:20. Extract yields were not affected by the scale-up process (bench: 4.67±0.14%; pilot: 4.37±0.19%). No significant differences were observed in either the total phenolics content of the extracts (bench: 0.55±0.01g gallic acid/g extract; pilot: 0.54±0.01g gallic acid/g extract) or the tannin content (bench: 340.0±7.4mg catechin/g extract; pilot: 334.0±4.4mg catechin/g extract). The main low molecular weight compounds identified in the extracts were phenolic acids, catechin, epicatechin, procyanidin B-2, taxifolin and quercetin; to the best of our knowledge, we have tentatively identified syringic acid and homovanillic acid in pine bark for the first time. An increase in the average molecular weight (Mw) of the extract also changed with the extraction scale (bench: Mw=1689; pilot: Mw=2299). The antioxidant properties of the extracts showed a decrease in DPPH (-6.12%) and FRAP (-6.88%) and an increase in ICA (21.63%) in the pilot-scale as compared to the bench-scale extract. Based on these results, it may be technically possible to produce a polyphenolic extract from P. radiata bark at an industrial scale without extensively altering its antioxidant properties.