Polysaccharide from Lycium arabicum: Structural Features, in Vitro Antioxidant Activities and Protective Effect against Oxidative Damage in Human Erythrocytes.

In this research work, a water-soluble polysaccharide (LAP) isolated from the fruits of Lycium arabicum was investigated. LAP contains carbohydrates (82.45±1.23 %), protein (1.56±0.21 %), and uronic acids (3.56±0.34 %). The analysis of the monosaccharide composition revealed the presence of rhamnose, arabinose, galactose, glucose and mannose in a molar ratio of 4.7 : 1.5 : 1 : 8.7 : 16.4 : 5.6. The extracted polysaccharide (PS) was considered as heterogeneous and highly branched by interpreting its GC/MS, FT-IR and NMR data. Crystallinity of LAP was inferred from its X-ray diffractometry (XRD) and Scanning Electron Microscopy (SEM) analysis. LAP exhibited an interesting stability at high temperatures (∼254 °C) and in a wide range of pH (3-9) deduced, respectively, from its DSC and zeta potential analysis. LAP displayed a strong antioxidant activity at low concentrations evaluated by the 2,2-diphenyl-1-picrylhydrazyl (DPPH)-radical scavenging, ferric reducing activity power (FRAP), free radical scavenging ability, superoxide radical-scavenging and hydroxyl radical-scavenging abilities. Inhibition of erythrocyte hemolysis and lipid peroxidation was also assessed. In 5 h, LAP treatment allowed the protection of the damaged erythrocytes caused by AAPH (2,2-azobis(2-amidinopropane) dihydrochloride), to reduce the level of malondialdehyde (MDA) as well as to increase the reduced glutathione (GSH) level.

Agricultural wastes as substrates for ß-glucosidase production by Talaromyces thermophilus: Role of these enzymes in enhancing waste paper saccharification.

In the present study, we investigated a potent extracellular ß-glucosidases secreted by the thermophilic fungal strain AX4 of Talaromyces thermophilus, isolated from Tunisian soil samples. This strain was selected referring to the highest thermostability of its ß-glucosidases compared to the other fungal isolates. The ß-glucosidase production was investigated by submerged fermentation. The optimal temperature and initial pH for maximum ß-glucosidase production were 50°C and 7.0, respectively. Several carbon sources were assayed for their effects on ß-glucosidase production, significant yields were obtained in media containing lactose 1% (3.0 ± 0.36 U/ml) and wheat bran 2% (4.0 ± 0.4 U/ml). The combination of wheat bran at 2% and lactose at 0.8% as carbon source enhanced ß-glucosidase production, which reached 8.5 ± 0.28 U/ml. Furthermore, the ß-glucosidase-rich enzymatic juice of T. thermophilus exhibited significant synergism with Trichoderma reesei (Rut C30) cellulases for pretreated waste paper (PWP) hydrolysis. Interestingly, the use of this optimal enzymatic cocktail increased 4.23 fold the glucose yield after saccharification of waste paper. A maximum sugar yield (94%) was reached when using low substrate (2%) and enzyme loading (EC1).

Enzymatic hydrolysis of pretreated Alfa fibers (Stipa tenacissima) using ß-d-glucosidase and xylanase of Talaromyces thermophilus from solid-state fermentation.

This work aims at realizing an optimal hydrolysis of pretreated Alfa fibers (Stipa tenacissima) through the use of enzymes produced from Talaromyces thermophilus AX4, namely ß-d-glucosidase and xylanase, by a solid state fermentation process of an agro-industrial waste (wheat bran supplemented with lactose). The carbon source was firstly selected and the optimal values of three other parameters were determined: substrate loading (10g), moisture content (85%) and production time (10days); which led to an optimized enzymatic juice. The outcome was then supplemented with cellulases of T. reesei and used to optimize the enzymatic saccharification of alkali-pretreated Alfa fibers (PAF). The maximum saccharification yield of 83.23% was achieved under optimized conditions (substrate concentration 3.7% (w/v), time 144h and enzyme loading of 0.8 FPU, 15U CMCase, 60U ß-d-glucosidase and 125U xylanase).The structural modification of PAF due to enzymatic saccharification was supported by the changes of morphologic and chemical composition observed through macroscopic representation, FTIR and X-Ray analysis.

Physicochemical properties of thermotolerant extracellular ß-glucosidase from Talaromyces thermophilus and enzymatic synthesis of cello-oligosaccharides.

A thermophilic fungus, Talaromyces thermophilus that produces a novel thermotolerant extra-cellular ß-glucosidase (Bgl.tls), was isolated from Tunisian soil samples. The enzyme was purified from the culture filtrates of T. thermophilus grown on lactose using gel filtration, ion exchange chromatography and FPLC. The monomeric enzyme had a molecular mass of 116.0 kDa and a high specific activity of 1429 UI/mg. Bgl.tls exhibited optimal activity at pH 5.0 and 65 °C. It was also stable over a wide range of pH (4.0-10.0) and stable at 50 °C for 34 h. Bgl.tls retained about 80% of its initial activity after 1.0 hours of preincubation at 60 °C. The Km and Vmax values recorded for pNPG were 0.25 mM and 228.7 µmol min(-1), respectively. Bgl.tls was activated by Mn(2+), Mg(2+), Ca(2+) and Co(2+) but obviously inhibited by Fe(2+) and Cu(2+). It was able to hydrolyze a variety of aryl / alkyl -ß-glucosides and disaccharides as well as (1 → 6) and (1 → 4)-ß-glucosidic linkages and α-glycosidic substrates, thus providing evidence for its broad substrate specificity. The enzyme also displayed high hydrolytic and transglycosylation activities. Overall, this study is the first report on the purification and physicochemical properties of a ß-glucosidase secreted by T. thermophilus. The cello-oligosaccharides synthesized by this enzyme within 2 h were mainly cellotriose, cellotetraose and cellopentaose identified by HPLC and ESI-MS techniques.