Esterification of polysaccharides catalyzed by naturally occurring a-hydroxy acids

EMA CAVALLO; MARIA LAURA FORESTI; ALEJANDO AVILA RAMIREZ; MARIBEL TUPPA; M INES ERREA; PATRICIA CERRUTTI

Jena

Congreso; 5th EPNOE International Polysaccharide Conference; 2017

1.Introduction: Esterification of polysaccharides is a well-known route to broaden their applications. In the case of starch, partial esterification provides the polysaccharide with specific properties which allow its use as additive in the food industry (mainly acetylated starch), and as tool for delivering specific short chain fatty acids to the colon (mainly propionylated and butyrylated starches), among others. On the other hand, in the field of composite materials, controlled esterification of highly hydrophilic cellulose nanofibers is of wide interest for improving their dispersibility/compatibility with hydrophobic polymeric matrices. Esterification of starch has been mainly performed in NaOH medium, whereas cellulose nanofibers esterification has been mainly catalyzed by H2SO4 and HClO4.2.Objectives: The aim of the current contribution is to assay the suitability of chosen naturally occurring -hydroxy acids (L-(+)-tartaric and citric acids) as catalysts for the production of propionylated starch derivatives with high resistant starch (RS) content, and in the acetylation of bacterial cellulose nanoribbons (BC) to be used as reinforcement of hydrophobic polymeric matrixes.3.Materials & methods: Dried corn starch (12.3 mmol AGU) or solvent exchanged BC (3.1 mmol AGU), α-hydroxy acids (0.1?3.3 mmol/mmol AGU) and the corresponding acylants (propionic acid, 125 mmol, or acetic anhydride, 530 mmol) were contacted at 130 °C during varying reaction time intervals (0.5-7 h). The reaction products were characterized in terms of degree of substitution (DS), chemical structure, morphology, crystallinity, and RS content/nanofibers wettability. 4.Results: Results illustrated the catalytic activity of the α-hydroxy acids assayed. Proper manipulation of catalyst concentration and reaction time, allowed obtaining propionylated starches with DS=0.05-0.70, and acetylated BC nanofibers with DS=0.20-0.70 (time ≤ 7 h). Propionylated starches showed RS contents of up to 50 wt. %, whereas characterization of derivatized BC evidenced hydrophobization and a surface-only process. 5.Conclusion: Tartaric and citric acids of natural origin have shown a promising catalytic activity for the production of esterified starch and bacterial cellulose with varying DS and associated target properties.