Optimization of Polyphenols Extraction Using Response Surface Methodology and Application of Near Infrared Spectroscopy to Phenolic Content Analysis of Pine Bark
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Date
2010
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Abstract
The utilization of pine bark for processing water resistant phenol-formaldehyde adhesive for
plywood production encounters difficulties due to the very high reactivity of the
formaldehyde condensable phenolics and other un-intended compounds (sugars) extracted
into solution, as well as time consuming and costly chemical analysis. The potential of near
infrared reflectance spectroscopy (NIRS) for rapidly and accurately determining the
polyphenolic contents in Pinus caribaea bark extracts was assessed by means of multivariate
calibration techniques. To optimize the polyphenol content, four different solvents (aqueous
acetone, aqueous ethanol, aqueous NaOH and water) were used in the extractions. Batch
experiments were performed at different solvent concentrations, time, temperature and liquidsolid
ratio. Mathematical polynomial models were proposed to identify the effects of
individual interactions of these variables on the extraction of polyphenols and optimum
content using response surface methodology (RSM). The optimized conditions were used to
extract polyphenols which were used in the formulation of resol resins for plywood
manufacture. The first derivative spectra with PLS regression were found to provide the best
prediction of the tannin content and Stiasny number of pine bark with a SECV = 0.14 and
1.26 and r2 = 0.97 and 0.95 respectively. The predicted values were thus highly correlated
with costly measured values of tannin content and Stiasny number. The highest extraction
model efficiency (78.98%) was observed for aqueous extraction when only tannin content
was maximized in the numerical optimization process. This corresponded to optimum
extraction conditions of 69°C extraction temperature, 126 min extraction time and 23:1
liquid-solid ratio. The RSM model that gave a high tannin content (18.85%) with a
corresponding good quality resin (shear strength = 2.4 MPa, 10% delamination) was found
for aqueous ethanol extraction when the objective function was to maximize both the tannin content and Stiasny number and minimize the sugar content simultaneously.
Description
A thesis submitted to the Department of Chemical Engineering,Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Doctor of Philosophy.