title: Immobilized Sclerotinia sclerotiorum invertase to produce invert sugar syrup from industrial beet molasses by-product.
abstract: The fungus Sclerotinia sclerotiorum produces invertase activity during cultivation on many agroindustrial residues. The molasses induced invertase was purified by DEAE-cellulose chromatography. The molecular mass of the purified enzyme was estimated at 48 kDa. Optimal temperature was determined at 60 °C and thermal stability up to 65 °C. The enzyme was stable between pH 2.0 and 8.0; optimum pH was about 5.5. Apparent K(m) and V(max) for sucrose were estimated to be respectively 5.8 mM and 0.11 μmol/min. The invertase was activated by β-mercaptoethanol. Free enzyme exhibited 80 % of its original activity after two month's storage at 4 °C and 50 % after 1 week at 25 °C. In order to investigate an industrial application, the enzyme was immobilized on alginate and examined for invert sugar production by molasses hydrolysis in a continuous bioreactor. The yield of immobilized invertase was about 78 % and the activity yield was 59 %. Interestingly the immobilized enzyme hydrolyzed beet molasses consuming nearly all sucrose. It retained all of its initial activity after being used for 4 cycles and about 65 % at the sixth cycle. Regarding productivity; 20 g/l of molasses by-product gave the best invert sugar production 46.21 g/day/100 g substrate related to optimal sucrose conversion of 41.6 %.
authors.affiliation: Laboratory of Protein Engineering and Bioactive Molecules (LIP-MB), National Institute of Applied Sciences and Technology, University of Carthage, B. P. 676, 1080, Tunis Cedex, Tunisia, mouelhirefka@yahoo.fr.
authors.forename: Refka
authors.initials: R
authors.lastname: Mouelhi
authors.forename: Ferid
authors.initials: F
authors.lastname: Abidi
authors.forename: Said
authors.initials: S
authors.lastname: Galai
authors.forename: M Nejib
authors.initials: MN
authors.lastname: Marzouki
mesh_terms: D001203:Ascomycota / Q000201:enzymology*; D027461:Beta vulgaris; D002852:Chromatography, Ion Exchange; D020536:Enzyme Activators / Q000378:metabolism; D004795:Enzyme Stability; D004800:Enzymes, Immobilized / Q000378:metabolism*; D005632:Fructose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008623:Mercaptoethanol / Q000378:metabolism; D008965:Molasses; D008970:Molecular Weight; D013696:Temperature; D043324:beta-Fructofuranosidase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D020536:Enzyme Activators; D004800:Enzymes, Immobilized; D005632:Fructose; D008623:Mercaptoethanol; D043324:beta-Fructofuranosidase; C008133:invert sugar; D005947:Glucose