Optimum Acetone and Ethanol Extraction of Polyphenols from Pinus caribaea Bark: Maximizing Tannin Content Using Response Surface Methodology

Abstract

The bark extracts of various commercially important trees contain polyphenolics, which in the form of tannins can form condensation products with formaldehyde to produce wood adhesives. In the present work, aqueous acetone and aqueous ethanol were used as solvents to extract tannin from Pinus caribaea bark. The Stiasny number was determined as well as the amount of sugar co-extracted. Batch experiments were performed at different extraction times (30-180 min), extraction temperature (35-60°C for aqueous acetone; 35-80°C for aqueous ethanol), solvent concentration (10-100 percent), stage extraction (1-6) and liquid-solid ratio (10-50). A mathematical model was proposed to identify the effects of the individual interactions of these variables on the extraction of tannin using the two different solvents. The results have been modeled using response surface methodology. The response surface method was developed using five levels (-2, -1, 0, +1, +2) with the above mentioned factors except the stage extraction factor. The second order quadratic regression model fitted the experimental data with Prob > F to be < 0.0001 for the aqueous ethanol extraction and Prob > F to be < 0.006 for the aqueous acetone extraction. The experimental values were found to be in good agreement with the predicted values, with a satisfactory correlation coefficient of R2 = 0.82 in the case of aqueous ethanol extraction and R2 = 0.45 in the case of aqueous acetone extraction. The maximum predicted tannin yield of 20.68 percent was obtained under the optimum extraction conditions of 71.46°C extraction temperature, 79.2 min extraction time, 21.9 percent ethanol concentration, and 26.4:1 liquid-solid ratio. The amount of total sugars and the Stiasny number predicted under these conditions were 4.94 percent and 80.47 percent, respectively.