Monday, April 19, 2010
3-07

Isolation and selection of filamentous fungi for producing hydrolytic enzymes of cassava starch

Andres M. Rueda1, Clara S. Sanchez1, Rodrigo Torres2, and Daniel Molina2. (1) Bacteriology and Clinical Laboratory School, Universidad Industrial de Santander, FACULTAD DE SALUD Carrera 32 No 29 – 31 oficina 421, Grupo de Investigacion en Bioquimica y Microbiologia, Bucaramanga, Colombia, (2) School of Chemistry, Universidad Industrial de Santander, Ciudad Unviersitaria. Edificio Camilo Torres. Laboratorio de Bioquímica., Grupo de Investigación en Bioquímica y Microbiología, Bucaramanga, NA, Colombia

Production of fermentable sugars from cassava starch is commonly carried out by enzymatic hydrolysis of gelatinized starch. In general, enzymes that specifically hydrolyze starch in the saccharification process are named amylases. Among these are glucoamylases that produce glucose from dextrins. Glucoamylases are commercialized like enzymatic extracts. In this work, fifteen microorganisms were isolated from bitter cassava samples (Manihot sp,) with fungal colonization. For the first isolation, a culture medium with maltose as only carbon source was used. Identification of microorganisms was made by growth in PDA media and microscopy. In addition, growth cultures of these microorganisms were carried out during 72 hours to establish maltose uptake and glucose formation. The 100% of isolated microorganisms, presented saccharolytic activity. We selected 3 fungi, Aspergillus A1, Aspergillus A11 and Aspergillus A12, that showed maximum glucose production (3,6 gr/l, 3,1 gr/l and 3,5 gr/l, respectively) in the fermentation broth. Enzymatic extracts of this last fungus was made for filtration and quantified maltose, glucose, proteins and cell concentrations (by 3,5 dinitrosalycilic acid, glucose oxidase, Bradford, and cell dry weight methods, respectively). Finally, we made partial purification of glucoamylase by protein precipitation with salts and organic solvents (ethanol, acetone), concentrated by membrane ultrafiltration and biochemically characterized by SDS-PAGE.

Keywords: Glucoamylase, Starch, Aspergillus, Fungal Biotechnology


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