RESUMO
The effects of reaction conditions on cyclodextrins (CDs) production by CGTase from newly isolated Bacillus agaradhaerens KSU-A11 is reported. Among six types of starch tested, potato starch gave highest starch conversion into CDs. In addition, CDs yield was about three fold higher when using gelatinized potato starch in comparison to raw starch. The total CDs production was increased with increasing pH, showing maximum starch conversion at pH 10. Furthermore, the proportion of gamma-CD was relatively higher under slightly acidic-neutral conditions than at alkaline pH with a maximum proportion of 35.6 percent at pH 7 compared to 7.6 percent at pH 10. Maximum starch conversion into CDs was seen at reaction temperature of 55ºC. Lower reaction temperature led to higher proportion of gamma-CD with maximum percentage at 35ºC. Cyclization reaction was significantly promoted in the presence CaCl2 (10 mM), while in the presence of ethyl alcohol there was significant decrease in CD production particularly at high concentration. beta-CD was the major product up to 1 hr reaction period with traces of alpha-CD and no detectable gamma-CD. However, as the reaction proceed, gamma-CD started to be synthesised and alpha-CD concentration increased up to 4 hrs, where the CDs ratios were 0.27:0.65:0.07 for alpha-CD:beta-CD:gamma-CD, respectively. In addition, optimum CGTase/starch ratio was obtained at 80 U/g starch, showing highest starch conversion into CDs. All the parameters involved have been shown to affect the products yield and/or specificity of B. agaradhaerens KSU-A11 CGTase.
Assuntos
Bacillus/isolamento & purificação , Bacillus/enzimologia , Ciclodextrinas/biossíntese , Glucosiltransferases/metabolismo , Ativação Enzimática , Ensaios Enzimáticos , Concentração de Íons de Hidrogênio , Especificidade por Substrato , TemperaturaRESUMO
The use of enzymes in supercritical CO(2) (SCCO(2)) has received extensive attention in recent years. Biocatalysts have the advantage of substrate specificity and SCCO(2) offers several advantages over liquid solvents. This work deals with the utilization of SCCO(2) as a medium for the enzymatic removal of phenol from aqueous solutions using tyrosinase. Since the presence of oxygen is crucial for the enzyme-catalyzed oxidation, the substantial solvating power of SCCO(2) makes it a promising medium for such reactions. The conversion of phenol was higher at 10 MPa. Under near critical conditions (7 MPa, 35 degrees C), the addition of air at 5 x 10(5) Pa of pressure improved phenol removal.