# Single-Stage Fractionation of Vine Shoots Using Microwave Heating
## 3 Results and Discussion
### Characterization of Oligosaccharides from Vine Shoot Hemicelluloses  
The type and relative proportions of structural units and substituents in streams AqO, R1 and R2 were studied by HPLC, HPSEC, and HPAED-PAD (see Figure 6).  
In the HPLC chromatograms (Figure 6a), the monosaccharides appeared at retention times between 20 and 28 min. The peaks eluted at shorter times corresponded to compounds included in the OS fraction, in order of decreasing DP. For comparison, the Figure includes the peaks corresponding to XOS standards of DP 2-3. In the chromatograms obtained for AqO and R1, the concentration effects caused by DDVR can be observed. As a result of the xylanase stage, the product distribution determined for R2 is defined by the increased presence of low DP OS (in the range 2 and 3). The membrane step also caused the removal of 1-butanol (elution time, 44.5 min). The HPSEC chromatograms recorded for AqO, R1 and R2 (see Figure 6b) showed complex elution profiles, confirming diverse structural patterns for the substitution of the backbones composed of xylose units. The data revealed the presence of diverse compounds and substituents, including pentoses, hexoses and AG. The experimental data confirmed the major findings explained above concerning the concentration and DP distribution of the target compounds in streams AqO, R1 and R2. HPAEC-PAD provided additional information on the compounds contained in the OS fraction (see Figure 6c). The samples subjected to HPAEC-PAD analysis lacked AG substituents, which were saponified by the alkaline mobile phase [40]. The peaks corresponding to xylobiose (eluted at 34.2 min) and xylotriose (eluted at 38.8 min) in the chromatograms recorded for streams AqO, R1 and R2 clearly showed the generation of low-DP OS in the enzymatic step.  
The experimental data showed that Shearzyme behaved as an excellent catalyst for reducing the DP of xylan-hydrolysis products without concomitant xylose generation. This finding is in agreement with data reported in related studies dealing with the processing of diverse xylan-containing materials (rice husks, wheat straw, corn cobs, and sunflower stalks) [28; 41]. MALDI-TOF-MS spectra allowed the structural characterization of individual compounds making part of the OS fraction contained in AqO. The data are reported as sodium adducts of the respective compounds. OS below 500 m/z could not be identified because of the matrix interference (2,5-dihydroxybenzoic acid). Acetylated (A) backbones composed of pentose (P) chains, corresponding to the P\({}_{\text{n}}\)A\({}_{\text{m}}\) general structure, were identified. Their polymerization degree varied from P\({}_{3}\)A\({}_{\text{2}}\) to P\({}_{\text{7}}\)A\({}_{\text{5}}\). Additionally, compounds  
Figure 5: Composition of the aqueous streams (AqO, R1 and R2) involved in the membrane processing. Nomenclature: GOS, glucose units in oligosaccharides (OS); XOS, xylose units in OS; GaOS, galactose units in OS; AOS, arabines units in OS; MOS, mannose units in OS; AG, acetyl groups linked to OS; HMF, hydroxymethylfurfural; F, furfural; ONVC, other non-volatile compounds.  
bearing uronic substituents (U) were identified (P\({}_{6}\)A\({}_{5}\)U). The spectra also showed the presence of saccharides composed of hexoses (H) with a wide DP range (from H\({}_{3}\) to H\({}_{13}\)) in cases that were acetylated (such as H\({}_{10}\)A and H\({}_{10}\)A\({}_{2}\)). Based on the compositional data shown in Table 1 and Figure 5, the pentose chains type P\({}_{n}\)A\({}_{m}\) must be composed of xylose, whereas the hexoses correspond mainly to glucose, but also to galactose and mannose. The general structures deduced from the MALDI-TOF-MS data are in concordance with the ones reported for OS obtained from different lignocellulosic materials [6; 12; 13; 35].