Hemicelluloses from shoots and shells of the woody bamboo Guadua chacoensis obtained in different conditions

FERNÁNDEZ, P. V.; CAPARRÓS FRENTZEL, M. E.; COBELLO, L.; ZELAYA, V. M.; ANDREA S. VEGA; CIANCIA, M.

Barcelona

Simposio; 19th European Carbohydrate Symposium (EUROCARB 2017); 2017

EUROCARB

Woody bamboos are perennial evergreen plants belonging to Poaceae with very high rates of growth. Bamboo shoots are the new culms that arise from the rhizomes, containing nodes and internodes in a vertically miniaturized form, they are protected by culm leaves (shells). Recently, chemical characterization of cell wall polysaccharides from leaves of Guadua chacoensis was carried out, and their use as forage was proposed [1]. In a project devoted to study possible uses for this natural resource, native from the Americas, we studied the structure of cell wall polysaccharides obtained from shoots and shells in different extraction conditions.The classic alkaline extraction of hemicelluloses showed huge differences in composition regards their yield and structure. While extracts obtained with 1M KOH from shoots, which represent 10.3% of AIR, were mostly glucuronoarabinoxylans (GAX), those obtained from shells, which represented 23.0% of AIR, had major quantities of mixed linkage glucans (MLG) (88%GAX and 9% MLG, and 42%GAX and 58% MLG, respectively). This pattern was repeated in all the alkaline extracts, their structure was investigated by methylation analysis and NMR spectroscopy. In both resources, terminal α-D-galactose, α-D-glucuronic, and 4-O-methyl-α-D-glucuronic acids (very clear in the NMR spectra) constitute, along with α-L-arabinofuranose, the ramifications of the xylan backbone, although GAX from shoots had less degree of ramification than those from shells. Extracts from shells were further purified by aqueous solubilization of GAX and fractions enriched in MLG were obtained. The ratio (1→3)/ (1→4)-linkages was determined.On the other hand, extraction of hemicelluloses from shoots with DMSO (twice) allowed determination of the substitution pattern respect to acetyl groups and ferulic acid, which were lost, when these polysaccharides were obtained by alkaline extraction. However, yields were lower, and the GAX obtained in this conditions were very different, not only respect to those substituents, but also regards the carbohydrates ramification pattern (which was much higher), showing the great importance of these conditions determining the characteristic of the product for further applications. Although considerable amounts of phenolics were present in these extracts (100.6 and 48.8 μg/g, respectively), these compounds were not clearly detected in the NMR spectra. Conversely, it was possible to determine substitution with acetyl groups.In conclusion, in this work the structural features of hemicelluloses from shoots and shells from G. chacoensis were determined, showing that it is possible to obtain GAX with different substitution patterns, depending which part of the plant is utilized, and the extraction conditions. Besides, shells, a material usually considered as waist, appear as a potential source of MLG.