A critical assessment of a viscometric assay for measuring Saccharomycopsis fibuligera α-amylase activity on gelatinised cassava starch

A viscometric technique for measuring Saccharomycopsis fibuligera DSM-70554 α-amylase on gelatinised cassava starch aqueous solutions was assessed. The selected conditions for working over a reliable viscosity measurement range involved a starch concentration of 5% (w/v) and a shear rate of 0.168 1/s. Viscometric assay involved the determination of the slope of the decrease in viscosity with time of the starch solution consequent on enzyme addition. Thereafter, a calibration curve was constructed by plotting the slopes, expressed in arbitrary viscometric units (AVU), versus the corresponding absolute activity (in IU) of either the commercial α-amylase from Aspergillus oryzae (up to 0.1 IU) or the S. fibuligera DSM-70554 α-amylase (up to ca. 0.4 IU). The amount of enzyme expressed in absolute terms produced different liquefying activities according to the α-amylase tested, emphasising the necessity of this correlation to be carried out for the particular enzyme being measured. In this work, a linear relationship and a very good correlation factor were achieved for the calibration of both amylases. Likewise, α-amylase activities determined according to the conventional reducing sugar determination and the colorimetric assay with iodine were proportional to those viscometrically obtained, both for A. oryzae and S. fibuligera α-amylase, validating conversions between different units. The viscometric assay herein described showed to be specific and sensitive and, after its calibration, it allows to convert α-amylase measurements in absolute units thus facilitating future comparisons.