Purification and Characterisation of a Thermostable ß-Xylosidase from Aspergillus niger van Tieghem of Potential Application in Lignocellulosic Bioethanol Production.

A locally isolated strain of Aspergillus niger van Tieghem was found to produce thermostable ß-xylosidase activity. The enzyme was purified by cation and anion exchange and hydrophobic interaction chromatography. Maximum activity was observed at 70-75 °C and pH 4.5. The enzyme was found to be thermostable retaining 91 and 87% of its original activity after incubation for 72 h at 60 and 65 °C, respectively, with 52% residual activity detected after 18 h at 70 °C. Available data indicates that the purified ß-xylosidase is more thermostable over industrially relevant prolonged periods at high temperature than those reported from other A. niger strains. Maximum activity was observed on p-nitrophenyl-ß-D-xylopyranoside and the enzyme also hydrolysed p-nitrophenyl ß-D-glucopyranoside and p-nitrophenyl α-L-arabinofuranoside. The purified enzyme acted synergistically with A. niger endo-1,4-ß-xylanase in the hydrolysis of beechwood xylan at 65 °C. During hydrolysis of pretreated straw lignocellulose at 70 °C using a commercial lignocellulosic enzyme cocktail, inclusion of the purified enzyme resulted in a 19-fold increase in the amount of xylose produced after 6 h. The results observed indicate potential suitability for industrial application in the production of lignocellulosic bioethanol where thermostable ß-xylosidase activity is of growing interest to maximise the enzymatic hydrolysis of lignocellulose.

Some factors affecting tannase production by Aspergillus niger Van Tieghem.

One variable at a time procedure was used to evaluate the effect of qualitative variables on the production of tannase from Aspergillus niger Van Tieghem. These variables including: fermentation technique, agitation condition, tannins source, adding carbohydrates incorporation with tannic acid, nitrogen source type and divalent cations. Submerged fermentation under intermittent shaking gave the highest total tannase activity. Maximum extracellular tannase activity (305 units/50 mL) was attained in medium containing tannic acid as tannins source and sodium nitrate as nitrogen source at 30 °C for 96 h. All added carbohydrates showed significant adverse effects on the production of tannase. All tested divalent cations significantly decreased tannase production. Moreover, split plot design was carried out to study the effect of fermentation temperature and fermentation time on tannase production. The results indicated maximum tannase production (312.7 units/50 mL) at 35 °C for 96 h. In other words, increasing fermentation temperature from 30 °C to 35 °C resulted in increasing tannase production.

Some factors affecting tannase production by Aspergillus niger Van Tieghem

One variable at a time procedure was used to evaluate the effect of qualitative variables on the production of tannase from Aspergillus niger Van Tieghem. These variables including: fermentation technique, agitation condition, tannins source, adding carbohydrates incorporation with tannic acid, nitrogen source type and divalent cations. Submerged fermentation under intermittent shaking gave the highest total tannase activity. Maximum extracellular tannase activity (305 units/ 50 mL) was attained in medium containing tannic acid as tannins source and sodium nitrate as nitrogen source at 30 ºC for 96 h. All added carbohydrates showed significant adverse effects on the production of tannase. All tested divalent cations significantly decreased tannase production. Moreover, split plot design was carried out to study the effect of fermentation temperature and fermentation time on tannase production. The results indicated maximum tannase production (312.7 units/50 mL) at 35 ºC for 96 h. In other words, increasing fermentation temperature from 30 ºC to 35 ºC resulted in increasing tannase production.

Citric acid production by Aspergillus niger van. Tieghem MTCC 281 using waste apple pomace as a substrate.

A solid state fermentation process was tried for the production of citric acid from apple pomace left after juice extraction using Aspergillus niger van. Tieghem MTCC 281 spores as inoculum (36.8 × 10(4) spores/100 g of pomace). The yield of citric acid was optimized by varying the amount of methanol (1-5% v/w), temperature (25-35°C) and time of incubation (1-7 days) for fermentation process. Optimum yield of citric acid (4.6 g/100 g of pomace) was recorded with 4% (v/w) methanol after 5 days of incubation at 30°C.