# Single-Stage Fractionation of Vine Shoots Using Microwave Heating
## 3 Results and Discussion
### Refining of OS  
Since the fractionation treatments performed at 175 \({}^{\circ}\)C provided the maximum OS concentration, this temperature was selected for further experimentation. The corresponding aqueous phase (AqO) contained both OS and undesired, volatile compounds and non-volatile components making part of the ONVC fraction. Additionally, AqO also contained 1-butanol because of its partial miscibility. The purification of hemicellulose OS was conducted using a number of separation methods, including membranes. OS refining using membranes was applied to vine shoots [6] and to other types of biomass [12; 13; 34]. Membranes have been also employed for separating 1-butanol from the aqueous phase obtained in the organosolv treatment of sorghum bagasse [20]. Streams AqO, R1 and R2 in Figure 2 show the compositions indicated in Figure 5. The OS in AqO were mainly composed of anhydro xylose structural units. AG were present in XOS at a molar ratio 0.45:1 respect to xylose. In comparison, minor amounts of GOS, GaOS, AOS and MOS were also found in the aqueous media. The volumetric OS concentration (including substituents) reached 18.67 g/L. Monosaccharides (0.86 g/L) and ONVC (6.78 g/L) were contaminants, whose concentrations should be reduced. The volatile compounds (acid acetic, HMF and F) achieved a joint concentration of 1.64 g/L, whereas 1-butanol was found in the aqueous media at a high concentration (68.7 g/L). The first step of membrane processing (DDVR) allowed to remove 86.7 % of the 1-butanol present in the permeate P1 (see Figure 5), leaving a reentate (R1) containing 12.28 g 1-butanol/L together with monosaccharides and volatile compounds. However, the ONVC concentration after DDVR increased up to 12.23 g/L, almost proportionally to the increase observed for the concentration of total OS content (which reached 40.41 g/L). The XOS concentration increased remarkably (up to 28.46 g/L), with an almost proportional increase of the AG concentration. The DDVR stage performed using the 1 kDa membrane enabled to recover in R1 of more than 90% of OS contained in AqO, increasing the OS content from 71 g OS/100 g NVC in AqO up to 76.3 g OS/100 g NVC. [PERSON] et al. [34] reported on the enzymatic hydrolysis of OS from different sources for obtaining of low molecular weight oligomers. Following this idea, R1 was treated with Shearzyme endo-xylanas (see Figure 2) for decreasing the average DP of XOS. This stage proceeded without xylose generation. In a related study, a similar behavior was reported for the enzymatic hydrolysis of rice husk xylooligosaccharides [28]. The solution resulting from the xylanase processing of R1 was processed in a 0.3 kDa MWCO membrane to reduce the concentrations of ONVC and 1-butanol in the permeate (stream P2), whose concentrations in R2 dropped to 4.02 and 3.50 g/L, respectively. In the same stream, the OS concentration reached 51 g of substituted OS/L. Among OS, the XOS concentration accounted 36.5 g/L, keeping constant the degree of substitution by AG. The effluent R2 showed a final OS concentration of 92.23 g/100 g of NVC. Finally, R2 was freeze-dried to yield the refined product. Diverse separation technologies have been employed in studies dealing with the refining of XOS from different sources [6; 28; 34; 35; 39]. For example, [PERSON] et al. [28] and [PERSON] et al. [35] reported that consecutive stages of membrane diafiltration, concentration and enzymatic hydrolysis with xylanas enabled the manufacture of low DP OS with purities above 90%.