Starch Depolymerization with Diluted Phosphoric Acid and Application of the Hydrolysate in Astaxanthin Fermentation

José Domingos Fontana¹*, David Alexander Mitchell², Oscar E. Molina³, Anabella Gaitan³, Tânia M.B. Bonfim¹, Juliana Adelmann¹, Adelia Grzybowski¹ and Maurício Passos<sup>1

1</sup>LQBB – Biomass Chemo/Biotechnology Laboratory, Federal University of Paraná, Curitiba, BR–81531-990 Paraná, Brazil
²Department of Biochemistry and Molecular Biology, Federal University of Paraná, Curitiba, BR–81531-990 Paraná, Brazil
³PROIMI – Nacional University of Tucuman, San Miguel de Tucuman, Argentina

Article history:
Received February 8, 2007
Accepted January 14, 2008

Key words:
cassava starch, phosphorolysis, acid hydrolysis, depolymerization, phosphoric acid, astaxanthin

Summary:
An innovative alternative for cassava starch hydrolysis has been developed using diluted (about 0.1 %) phosphoric acid at 160 °C. This technology is advantageous for developing countries where enzyme costs are prohibitive and hydrochloric acid is currently the only catalyst used for starch depolymerization. Lower concentrations of the byproduct hydroxymethyl furfural (HMF) were generated during starch hydrolysis when using phosphoric acid as compared to hydrochloric acid at any given acidic pH. Glucose was the major product from phosphorolysed starch under most reaction conditions, although maltosaccharides with degrees of polymerization from 2 to 7 were also produced, with their relative amounts depending on hydrolysis conditions. Neutralization of the acid with aqueous ammonia produced a hydrolysate with sources of C (free sugars), P (phosphate), and N (ammonium) that could find several applications. We demonstrated one of these, namely the potential for the use of the hydrolysate as a fermentation feedstock, by cultivating the astaxanthin-producing red yeast Xanthophyllomyces dendrorhous on it. Cassava wastewater, a polluting byproduct of starch processing, was found to be a convenient source of nitrogen for this fermentation process.

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