Title: Extraction and recovery of pectic fragments from citrus processing waste for co-production with ethanol Authors
Submitted to: Journal of Chemical Technology & Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 30, 2012
Publication Date: June 20, 2012
Citation: Grohmann, K., Cameron, R.G., Kim, Y., Widmer, W.W., Luzio, G.A. 2012. Extraction and recovery of pectic fragments from citrus processing waste for co-production with ethanol. Journal of Chemical Technology & Biotechnology. DOI: 10.1002/jctb.3859. Interpretive Summary: We describe the production, isolation and characterization of inheritantly functional oligogalacturonate fragments, both highly methylesterified and demethylesterified, from citrus processing waste by a combination of chemical, biochemical and thermal processes. The process we explored involved treating citrus processing waste with steam for various times which solubilized pectin fragments. Two treatments were tested, one used the natural pH of the citrus peel waste and the second involved a pH adjustment to acidify the waste. The treatment time was also a variable tested. The resulting solubilized pectin fragments could be purified by the addition of ethanol prior to demethylesterification, which could be beneficial for manipulating the distribution of ionic islands along the linear polymeric regions of galacturonic acid that comprise the dominate structural component of pectin. The pectin fragments could also be demethylesterified, either by the addition of base or by a fungal enzyme, and purified by a method utilizing a dilute mineral acid. Extracting pectin fragments will enable more concentrated solutions to be produced than would be possible with high molecular weight pectin, that still maintain a high level functional potential.
Technical Abstract: Steam treatment of citrus processing waste (CPW) at 160°C followed by a rapid decompression (steam explosion) at either pH 2.8 or 4.5 provides an efficient and rapid fragmentation of protopectin in CPW and renders a large fraction of fragmented pectins, arabinans, galactans and arabinogalactans soluble in water. The treatment produced a mixture saccharides ranging in size from oligomers to polymers up to 700 x 103 g/mol in size for CPW treated at pH 4.5 for 1 min. Fragmented pectins were highly methylesterified (approximate DM 68%) and freely soluble in water. All polysaccharides from treatments at pH 4.5 seem to include materials high in MW, but hydrolysis was clearly observed during treatments at pH 2.8, yielding materials more uniform and lower in molecular weight. Relatively pure (up to 92%) pectin fragments were recovered by the precipitation with dilute mineral acid after demethylesterification. This result provides a strong evidence that the majority of arabinans, galactans and arabinogalactans are not covalently attached to the pectin backbone in these preparations. Methylesterified pectin fragments were also purified and recovered by precipitation with ethanol, but the purity of recovered pectic fragments was lower due to coprecipitation of galactans and to a lesser extent arabinans. The steaming process for preparation of pectic fragments is rapid and environmentally friendly because no toxic chemicals are introduced into the treatment and the other portion of the treated CPW can be used for the fermentations to produce ethanol and other compounds.