Polysaccharides from pinhão seeds of Araucaria angustifolia: Extraction, isolation and structural characterization

Abstract

Araucaria angustifolia is one of the main conifer species with great economic importance. Its seeds, known as pinhão, play a fundamental role in ecosystem conservation and have promising potential for application in the food/nutraceutical industry. This study aimed to elucidate the fine chemical structure of polysaccharides, showing for the first time the composition of non-starch polysaccharides present in the pinhão seeds. For this, the seeds were submitted to sequential extractions giving rise to the water polysaccharide (PW), and alkaline polysaccharides (PA2M), and (PA4M) fractions, obtained after aqueous, 2 mol L-1 and 4 mol L-1 NaOH extraction, respectively. The polysaccharides isolated showed the presence of glucose (between 96.8% and 76.3%) indicating starch as the main component of all fractions. Moreover, after enzymatic treatment, the PA4M-A fraction was obtained showing mostly arabinose in its monosaccharide composition. In this way, the chemical structure of PA4M-A was investigated by 1D 1H, 13C NMR and 2D 1H–13C HSQC, 1H–1H COSY and 1H–13C HMBC NMR spectroscopy, which demonstrated the presence of arabinans composed with a backbone of (1→5)-linked-α-L-arabinofuranosyl units substituted in O-2 and/or O-3 position by α-L-Araf-(1→ or α-L-Araf-(1→3)-α-L-Araf-(1→ side chains. The structural elucidation of the arabinans presents in the pinhão cell wall contributes to the knowledge of the molecular structure of the A.angustifolia seeds.