Enzyme-assisted extraction and product profiling of fucosylated xyloglucan from industrial citrus pectin residues

Industrial pectin production from citrus peels involves extended, multi-step acidic extraction at elevated temperatures. Pectin quality can be improved by reducing the extraction time or number of steps, but this comes at the expense of yield. A decrease in pectin yield revenue may be compensated for by developing new usage of the partially depectinized citrus residues. One option is to capitalize on the fucosylated xyloglucans present in the residues. Thus, the aim of this work was to maximize gentle extraction of fucosylated xyloglucan from partially depectinized citrus peel residues of orange and lemon and examine the effects of multi-step extraction on pectin quality. To maintain the structural integrity of the xyloglucan, an enzyme-assisted approach was used to release the xyloglucan from the fibrous pectin extraction residues, with a focus on enzymatic cellulose degradation. The performance of four commercial cellulase preparations were compared (Cellic CTec2, Cellic CTec3, ENZECO CE3, and ENZECO Glucanase PF) through a multivariate approach. All cellulase preparations, being multicomponent enzyme blends, induced partial degradation of xyloglucan simultaneously with the cellulose depolymerization; the lowest dosage of Cellic CTec2 (100 µL/g DM, 40 °C, pH 7.0) resulted in the highest yields of solubilized fucosylated xyloglucans of 53 % and 39 % from the depectinized lemon and orange residues, respectively. Following the enzymatic extraction, membrane filtration outperformed alcohol precipitation in separating the solubilized xyloglucan oligosaccharides (< 2 kDa) from the simultaneously released high molecular weight rhamnogalacturonan I-like structures (500-10 kDa). The data provide new options for improved valorization of industrial depectinized citrus residues.