title: Production, purification, and characterization of a low-molecular-mass xylanase from Aspergillus sp. and its application in baking.
abstract: An extracellular xylanase produced by a Mexican Aspergillus strain was purified and characterized. Aspergillus sp. FP-470 was able to grow and produce extracellular xylanases on birchwood xylan, oat spelt xylan, wheat straw, and corncob, with higher production observed on corncob. The strain also produced enzymes with cellulase, amylase, and pectinase activities on this substrate. A 22-kDa endoxylanase was purified 30-fold. Optimum temperature and pH were 60 degrees C and 5.5, respectively, and isoelectric point was 9.0. The enzyme has good stability from pH 5.0 to 10.0, retaining >80% of its original activity within this range. Half-lives of 150 min at 50 degrees C and 6.5 min at 60 degrees C were found. K(m) and activation energy values were 3.8 mg/mL and 26 kJ/mol, respectively, using birchwood xylan as substrate. The enzyme showed a higher affinity for 4-O-methyl-D-glucuronoxylan with a K(m) of 1.9 mg/mL. The enzyme displayed no activity toward other polysaccharides, including cellulose. Baking trials were conducted using the crude filtrate and purified enzyme. Addition of both preparations improved bread volume. However, addition of purified endoxylanase caused a 30% increase in volume over the crude extract.
authors.affiliation: Laboratory of Fungal Physiology, Department of Food Science and Biotechnology, Faculty of Chemistry, Quimica E, National University of México, UNAM, Ciudad Universitaria, CP 04510, México DF, México.
authors.forename: Norma A
authors.initials: NA
authors.lastname: Camacho
authors.forename: Guillermo
authors.initials: G
authors.lastname: Aguilar O
mesh_terms: D001230:Aspergillus / Q000145:classification / Q000201:enzymology* / Q000254:growth & development; D019149:Bioreactors; D001939:Bread; D003247:Conservation of Natural Resources / Q000379:methods; D003296:Cooking / Q000379:methods; D004789:Enzyme Activation / Q000187:drug effects; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000737:chemistry; D008970:Molecular Weight; D013045:Species Specificity; D013379:Substrate Specificity; D013696:Temperature; D043325:Xylan Endo-1,3-beta-Xylosidase; D014990:Xylans / Q000737:chemistry* / Q000145:classification / Q000378:metabolism; D014995:Xylosidases / Q000737:chemistry* / Q000145:classification / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D008670:Metals; D014990:Xylans; D014995:Xylosidases; D043325:Xylan Endo-1,3-beta-Xylosidase