Ultrasound-assisted extraction of hemicelluloses from grape pomace using response surface methodology

An ultrasound-assisted procedure was applied to the extraction of hemicelluloses from grape pomace at a mild temperature (20 degrees C). A Central composite design (CCD) was employed to optimize the ultrasound-assisted extraction (UAE) of hemicelluloses from grape pomace with the aim to maximize their extraction yield, and, also, the obtention of the main polymers forming this fraction: Xyloglucans (XLG), Mannans (MAN) and Xylans (XN). Extraction time (X-1), solid:liquid ratio (X-2) and KOH concentration (X-3) were the variables used to optimize the process. The conditions that maximize (1) the extraction yield of hemicelluloses and the contents of (2) XLG, (3) MAN and (4) XN, were: (1) X-1 = 2.6h; X-2 = 1:48 (W/V); X-3 = 0.4M, (2) X-1 = 2.9h; X-2 = 1 :57 (W/V); X-3 = 2.25M, (3)X-1 = 2.7h; X-2 = 1 :58(W/V);X-3 = 2.2M, and (4)X-1 = 3h; X-2 = 1:60 (w/v); X-3 = 2.3M, respectively. Under these conditions, the maximum extraction yield of hemicelluloses, XLG, MAN and XN contents were: similar to 7.9 +/- 0.2%, similar to 3.6 +/- 0.02%, similar to 1.1 +/- 0.04% and similar to 1.2 +/- 0.02%, respectively. Close agreement between experimental and predicted values was found. The results suggest that the ultrasound-assisted extraction could be a good option for the extraction of hemicellulosic polysaccharides from grape pomace at industrial level. (C) 2015 Elsevier Ltd. All rights reserved.