دانلود رایگان مقاله جداسازی و شناسایی glucuronoarabinoxylan استیله از باگاس نیشکر و کاه

ABSTRACT

Sugarcane bagasse and straw are generated in large volumes as by-products of agro-industrial production. They are an emerging valuable resource for the generation of hemicellulose-based materials and products, since they contain significant quantities of xylans (often twice as much as in hardwoods). Heteroxylans (yields of ca 20% based on xylose content in sugarcane bagasse and straw) were successfully isolated and purified using mild delignification followed by dimethyl sulfoxide (DMSO) extraction. Delignification with peracetic acid (PAA) was more efficient than traditional sodium chlorite (NaClO2) delignification for xylan extraction from both biomasses, resulting in higher extraction yields and purity. We have shown that the heteroxylans isolated from sugarcane bagasse and straw are acetylated glucuronoarabinoxylans (GAX), with distinct molecular structures. Bagasse GAX had a slightly lower glycosyl substitution molar ratio of Araf to Xylp to (0.5:10) and (4-O-Me)GlpA to Xylp (0.1:10) than GAX from straw (0.8:10 and 0.1:10 respectively), but a higher degree of acetylation (0.33 and 0.10, respectively). A higher frequency of acetyl groups substitution at position -(1→3) (Xyl-3Ac) than at position -(1→2) (Xyl-2Ac) was confirmed for both bagasse and straw GAX, with a minor ratio of diacetylation (Xyl-2,3Ac). The size and molecular weight distributions for the acetylated GAX extracted from the sugarcane bagasse and straw were analyzed using multiple-detection size-exclusion chromatography (SEC-DRI-MALLS). Light scattering data provided absolute molar mass values for acetylated GAX with higher average values than did standard calibration. Moreover, the data highlighted differences in the molar mass distributions between the two isolation methods for both types of sugarcane GAX, which can be correlated with the different Araf and acetyl substitution patterns. We have developed an empirical model for the molecular structure of acetylated GAX extracted from sugarcane bagasse and straw with PAA/DMSO through the integration of results obtained from glycosidic linkage analysis, 1H NMR spectroscopy and acetyl quantification. This knowledge of the structure of xylans in sugarcane bagasse and straw will provide a better understanding of the isolation-structure-properties relationship of these biopolymers and, ultimately, create new possibilities for the use of sugarcane xylan in high-value applications, such as biochemicals and bio-based materials.

4. Conclusions

Two different extraction procedures (PAA/DMSO and NaClO2/DMSO) were compared for the isolation of acetylated AGX from sugarcane bagasse and straw. In general, the PAA/DMSO method resulted in greater efficiency and selectivity. This mild isolation methodology, together with detailed structural analyses, provides evidence ofthe intramolecular Ara and acetyl substitution pattern in sugarcane xylans. We successfully developed an empiricalmodelfor themolecular structure of acetylated glucuronorabinoxylan (GAX) extracted from sugarcane bagasse and straw, integrating the results from methylation glycosidic linkage analysis, H1 NMR spectroscopy and acetyl quantification. We have found that GAX from sugarcane bagasse differs structurally from that of sugarcane straw. Bagasse GAX had a slightly lower glycosyl substitution molar ratio of Araf to Xylp (0.5:10) than xylan from straw (0.8:10), but a higher degree of acetylation (0.33 and 0.10 for bagasse and straw, respectively). The acetyl groups were attached predominantly to positions O-3 (53%), O-2 (37%) and O-2,3 (10%) of the Xylp units in bagasse GAX, and to positions O-3 (68%), O-2 (21%) and O-2,3 (10%) of the Xylp units in straw GAX. These changes in the substitution pattern modulate the conformation of the acetylated GAX, as evidenced by the elution patterns and size distributions under SEC and the absolute molar weight identification by light scattering. This new knowledge of the structure of xylan in sugarcane bagasse and straw biomasses will provide a better understanding of their behavior during chemical processing and, ultimately, create new possibilities for the use of xylan biopolymers in materials and products.