Enzymic synthesis of levan and fructo-oligosaccharides by <Emphasis Type="Italic">Bacillus circulans</Emphasis> and improvement of levansucrase stability by carbohydrate coupling |
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Authors: | Heba A El-Refai Ahmed F Abdel-Fattah Faten A Mostafa |
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Institution: | (1) Chemistry of Natural and Microbial Products Department, National Research Center, Dokki, Cairo, Egypt |
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Abstract: | Bacillus circulans was able to produce extracellular levansucrase using sucrose as carbon source optimally at 35°C. The enzymic synthesis of
levan and fructo-oligosaccharides was studied using a 50% ethanol fraction of crude extract. The molecular weight of the synthesized
levan was markedly affected by sucrose concentration, the molecular weight of levan decreased with increased sucrose concentration
up to 32% whereby fructo-oligosaccharides were isolated. Temperature and the reaction time clearly affected the conversion
of fructose to levan with molecular weight values ranging from 10 to 38 kDa. Identification of levan indicated that fructose
was the building unit of the levan obtained. Thermal and pH stabilities of B. circulans levansucrase could be improved by enzyme glycosylation using sodium metaperiodate treatment. Chemical modification provides
additional points of attachment of the enzyme to the support which offered the modified enzyme greater stabilization than
did the free enzyme. The modified enzyme exhibited thermal tolerance up to 50°C, where it retained 88.25% of its activity,
while the free enzyme only retained 64.55% of its original activity. The half-life significantly increased from 130 min for
the free enzyme to 347 min for the modified enzyme at 50°C, however, it increased from 103 min for the free enzyme to 210 min
for the modified enzyme at 60°C. Other properties i.e., the response to some metal ions as well as the ability to convert
higher substrate levels and tolerance to an extension of the reaction periods were also improved upon modification. Obviously,
the results obtained outlined the conditions leading to the formation of important high or low molecular weight or levan and
fructo-oligosaccharides suitable for different industrial applications. |
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Keywords: | B circulans Levan Levansucrase Modification Molecular weight Properties |
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