Guarana powder polysaccharides: Characterization and rheological properties of starch
2014
Dalonso, Nicole | de Oliveira Petkowicz, Carmen Lúcia
Guarana seeds are described to contain starch as the main constituent. In this work, two fractions of starch were isolated from guarana seeds using dimethyl sulfoxide. The samples, named GD‐I and GD‐II were characterized and their rheological properties investigated. ¹³C NMR analysis confirmed the presence of starch in both fractions. GD‐I showed higher amylose content (51.4%) than GD‐II (33.0%). Elution profiles of GD‐I and GD‐II by high performance size exclusion chromatography indicated they were heterogeneous and polydisperse and GD‐II had higher molar mass than GD‐I. The rheological behavior of solutions in concentrations of 10%, 15%, 20%, and 25% in dimethyl sulfoxide was evaluated. In all concentrations studied GD‐I had values of G′ higher than G″. GD‐II had higher values of G′ and apparent viscosity than GD‐I, due the higher molar mass and amylopectin content. GD‐II displayed a weak gel‐like behavior in concentrations above 15%. All solutions displayed a shear thinning behavior (flow behavior index < 1). The consistency coefficient (K) increased with an increase in the concentration of guarana seed starch and the values were higher for GD‐II. The best fit of the data was obtained with the Ostwald de Waele (power law) and Herschel‐Bulkley models.
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