1,721,386 research outputs found
HYDROLYSIS OF TOPINAMBUR (JERUSALEM-ARTICHOKE) FRUCTANS BY EXTRACELLULAR INULINASE OF KLUYVEROMYCES-MARXIANUS VAR BULGARICUS
No full textExtracellular inulinase from Kluyveromyces marxianus var. bulgaricus catalysed the hydrolysis of pure inulin and the extracts of fresh and dried topinambur (Jerusalem artichoke). At an enzyme concentration of 10 IU g-1 of substrate the three substrates were hydrolysed respectively to 65.3, 77.3 and 83.9%. The relationship between the extent of hydrolysis, reaction time and enzyme concentration was studied and a kinetic model of hydrolysis was derived
Glutathione release in extracellular form by S. cerevisiae strains
Full text linkGlutathione (GSH, L--glutamyl-L-cysteinyl-glycine) is the most abundant non-protein thiol compound widely present in living organisms, from prokaryotes to eukaryotes (Anderson 1998). It is synthesised intracellularly by the consecutive actions of -glutamylcysteine synthetase, feedback inhibited by GSH, and GSH synthetase. This tripeptide’s very low redox potential gives it the properties of a cellular redox buffer (Udeh and Achremowicz 1997). In living tissues, GSH plays a pivotal role in bioreduction, protection against oxidative stress, xenobiotic and endogenous toxic metabolite detoxification, enzyme activity and sulphur and nitrogen metabolism (Penninckx 2002). These characteristics make this active tripeptide an important aid and/or support for the treatment of numerous diseases, such as HIV infections, liver cirrhosis, pancreatic inflammations and aging (Wu et al., 2004). In addition, GSH is of interest in the food additive industry and sports nutrition (Lomaestro and Malone 1995).
Yeasts, in particular belonging to the genus Saccharomyces, are the most commonly used microorganisms on an industrial scale for GSH fermentative production; however GSH contents of the wild-type strains are usually variable (0.1 – 1% dw) and always in intracellular form (Rollini and Manzoni 2006).
The present research was aimed at obtaining GSH in extracellular form, released from cells, at high levels. Samples of S. cerevisiae (baker’s yeast) from different suppliers were tested, together with reference strains belonging to international collections. Cells were comparatively treated employing physical and chemical procedures. The best result (2.9 g/l, 90% of produced GSH in extracellular form) was achieved at 24 h reaction, employing lyophilised cells from compressed baker’s yeast. The possibility of obtaining GSH directly in extracellular form, skipping the downstream cell extraction step, represents an interesting opportunity of reducing GSH production cost and furthering the range of application and utilization of this molecule
EXTRACELLULAR INULINASE FROM 4 YEASTS
No full textFour strains of yeasts, Candida kefyr, Candida pseudotropicalis var. lactosa, Kluyveromyces cicerisporus and Kluyveromyces fragilis, were studied for the production of inulinase. High enzyme activity (22.4-32.0 U/mL; 9.7-16.0 U/mg protein) was detected in the culture supernatant when the yeasts were grown in a medium containing aqueous extract of fresh Jerusalem artichoke (topinambur) tubers as carbon source. Maximum inulinase activity was obtained at 28 °C for C. kefyr and C. pseudotropicalis, and 32 °C for K. cicerisporus and K. fragilis, in 6-day-old cultures. The inulinase activity for all four strains exhibited a pH optimum of 4.7, a temperature optimum of 60 °C; the activation energy ranged from 3.2 to 4.8 Kcal/mole, and the half-life at 45 °C from 25 to 40 h. Ultrafiltration and following dialysis of the supernatants gave a degree of purification of the crude enzyme varying from 5.9 to 12.0. In preliminary experiments with topinambur extract, 89 and 92% of saccharification of 5% fructan expressed as total carbohydrate to fructose at 6 h was obtained with C. pseudotropicalis and K. cicerisporus extracellular enzyme (1 U/mL), respectively
Isolation and characterization of the exopolysaccharide produced by Daedalea quercina
No full textThe production of exopolysaccharide (EPS) by a strain of the basidiomycete Daedalea quercina was investigated. Of seven different carbon sources, glucose and dextrins gave the highest crude polysaccharide yield (4.7-5 g 1-1, 55-60% carbohydrate content) in shake-flask cultures, at 14 days of fermentation. Experiments carried out in a 101 fermenter, at two different agitation speeds, gave the best results at 300 rpm, resulting in 12-14 g 1-1 of crude exopolysaccharide in 9-11 days. Fractionation of the EPS samples, carried out by tangential flow ultrafiltration, evidenced a single EPS fraction (MW > 30 000 Da) in samples from glucose, while two fractions (MW > 30 000 Da and 30 000 > MW > 10 000 Da) were present in samples from dextrins. Fractions characterization by HPLC and proton NMR spectroscopy revealed diversity in composition and structure in the obtained EPS: from glucose mainly an α-linked mannan, and from dextrins mainly an α- and β-linked glucan
PURIFICATION AND CHARACTERIZATION OF THE EXTRACELLULAR INULINASE FROM KLUYVEROMYCES-CICERISPORUS
No full text- …
