Hot water extraction of hemicellulose from agricultural residues : influence of temperature and residence time

Abstract

Agricultural residues, a significant type of food waste, offer the opportunity to extract value-added compounds for eco-friendly and economically viable products. Hot Water Extraction (HWE) is a cost-effective, non-corrosive hydrothermal technique which can be used to extract bio-compounds like hemicellulose from agricultural residues. Optimizing the HWE process is essential to maximize the yield of these bio-compounds. This master’s study explores the potential of some agricultural residues, including coffee parchment (CP), coffee wood (CW), and cocoa pod husk (CPH), as feedstock for hemicellulose extraction using HWE. The research aims to optimize extraction conditions through response surface analysis, focusing on temperature and residence time. A Central Composite Design (CCD) was developed to determine suitable temperature and residence time combinations (103°C - 217°C, 11.7 - 68 minutes). Residue samples were treated in an HWE batch reactor, and extensive characterization was done for the recovered liquid and solid fractions. Results showed that temperature and time significantly influence the extraction of hemicellulose from CPH, CP, and CW. Response surface analysis indicated that the interaction mostly changed in a quadratic way. The optimal extraction conditions for arabinose and xylose were consistent across all samples, occurring at 160°C for 68 minutes. For CP and CW, the highest rhamnose and galactose concentrations were also obtained under the same conditions, while CPH reached its peak for these sugars at 160°C but at a short reaction time of 40 minutes. The optimal conditions for other hemicelluloses varied: for CPH a peak extraction of glucuronic acid and mannose was obtained at 160°C for 68 minutes, whereas CP and CW each required distinct conditions for optimal compound extraction.