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Influence of metal ions on purified xylanase activity and xylooligosaccharide production by enzymatic xylan hydrolysis
Gabrielle Victoria Gautério
Escola de Química / Universidade Federal do Rio de Janeiro
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Crie um tópicoEndo-β-1,4-xylanases are the main enzymes involved in xylan hydrolysis to produce xylooligosaccharides (XOS). Some metal ions can influence xylanases' catalytic performance and stability, making their influence relevant for subsequent enzyme application. This study aimed to evaluate the effect of metal ions on purified xylanase activity and xylan hydrolysis. Purification of xylanase from Aureobasidum pullulans CCT 1261 occurred by two-steps precipitation (0-20%/20-60%) with (NH4)2SO4 followed by a dialysis procedure. The influence of metal ions (K+, Na+, Ca2+, Zn2+, Mg2+, Cu2+ and Fe3+ as chloride salts) on xylanase activity was investigated at four concentrations (1, 5, 10 and 15 mmol/L). In addition, the effect of Ca+2 (10 mmol/L) was evaluated on xylanase stability (T: 45 °C, 50°C and 55 °C; pH: 4.5, 5.0 and 5.5) and XOS production by xylan hydrolysis. The reaction to produce XOS occurred at 3% (w/v) of beechwood xylan in sodium citrate buffer (50 mmol/L, pH 4.5), 200 U/g of purified enzyme, 180 rpm, 45 °C and 24 h. As a result, Ca+2, Zn+2 and Fe+3 increased the xylanase activity, while other ions inhibited it. The Ca2+ (10 mmol/L) stood out due to the highest increase (44%) in xylanase activity. The purified xylanase showed greater thermal stability (t1/2=169 h) at 45 °C and pH 4.5, and under these conditions and in the presence of Ca2+ (10 mmol/L), the enzyme was even more stable (t1/2=231 h). In xylan hydrolysis, the total XOS content (6.6 mg/mL) and XOS yield (22%) did not show significant difference (p>0.05) by addition of Ca2+ in the medium. However, the Ca2+ contributed positively to the xylobiose abundance (from 47.2% to 56.6%) and low xylose release (from 35.8% to 28.2%). In conclusion, Ca+2 showed a good effect to improve xylanase activity and stability and to obtain hydrolysates rich in xylobiose and with low xylose amounts.
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