Emilia Curotto

Aspergillus sp. 2M1 produces high levels of β -xylanases and β-xylosidases. Different carbon sources as inductors of xylanases were used. Production of xylanases were evaluated in a combined packed-bed/air-lift bioreactor (PBAL) in free and immobilized form and with a stationary tray bioreactor (STB). In the free form, xylanase activity was similar to that in Erlenmeyer flasks, but in the immobilized form higher values were observed Similar xylanases activities with the STB were found In order to understand xylanases stabilities, chemical modifications were done. Among others, 1-ethyl-3(3-dimethyl aminopropyl) carbodiimide (EDC) affected the xylanase activity. On the basis of this study, it was concluded that one or more carboxyl groups are in the active site of the xylanase from Aspergillus sp. 2M1. Xylanases induced by oatt birch and pinus xylans exhibited their optimum pH at 5.5 and at 55°C. At this temperature the half-lives of the xylanase activities were 11.8, 7.2 and 4.4 min for pinus, birch and oat, respectively. Xylanases induced by birch xylan were applied for a pre-bleaching experiment. Pre-bleaching of pinus Kraf pulp followed by a short oxygen-peroxide sequence, resulted in a very high selectivity as compared with commercial xylanases.

the problems and opportunities associated with fats. This short, easy-to-read booklet, written by Prof. A.S. Truswell, is based on the symposium. It deals with some nutritional aspects of fats (effects on plasma cholesterol, cancer-energy intake relationship) and food technologists’ problems and achievements in producing reduced-fat and reduced-saturated-fat food using fat mimetics and substitutes.

Transglutaminase (TG) is an enzyme that catalyzes an acyl-transfer reaction between the γ-carboxyamide group of peptide or protein-bound glutaminyl residues, and primary amines. TG action on protein molecules, causes a cross-linking and polymerizing effect of these latter, through ε-(γ-...

BIOTECHNOLOGY TECHNIQUES Volume 7 No.1 I (November 1993) p.821-822 Received as revised 27th September ... NEW METHODOLOGY FOR FUNGAL SCREENING: XYLANOLYTIC ENZYMES ... E. Curotto*", C. Aguirre', M. Concha", A. Nazal', V. Campose, E. Esposito", ...

Xylanase production by Penicillium janthinellum using 10-100 mM of 2,2-dimethylsuccinate (DMS) buffer, in a range of pH 4.5-6.0 was studied. The enzyme activity was enhanced using oat xylan as the carbon source. Under these conditions a culture produced 1.14 mumol/min (11.4 U/mL or 84.4 U/mg) of beta-xylanase after 5 d of growth in a 10-mM buffer solution at pH 4.5. Protease was absent in the DMS buffer except when 100 mM phosphate buffer at pH 6.0 was used (4 U/mL). beta-Xylosidase was only found at a pH of 4.5 in all the buffer concentrations. At a 50 mM DMS buffer concentration at pH 4.5 beta-xylanases were induced by both oat and birch xylans, having a greater effect with oat spelt xylans. Electrophoretic analyses showed that the birchwood xylan induction exhibited different proteins profiles. No beta-xylosidase or beta-glucosidase was induced until d 5. The beta-xylanases were rapidly inactivated at 50 degrees C, however, birch xylanase appeared to be more stable than oat xylanase. Using oat xylan as an inductor, the beta-xylosidase and beta-glucosidase were 85 and 91 U/L, respectively, on d 7. The xylanase produced by induction from sugar cane bagasse hydrolyzate was used for pulp biobleaching. A 20% decrease on the Kappa value in Kraft pulp using the culture extract was obtained. These selective growth conditions led us to modulate the xylanase production for pulp delignification.