Abstract
Enzymatic degradation of chitosan (degree of acetylation (da) and average viscosimetric molecular weight (MV) of 0.85 and 310 kDa, respectively) was carried out using commercial bromelain. Decrease of the average viscosimetric polymerization degree (XV) was studied in a buffer solution of acetic acid (0.3 M)/sodium acetate (0.2 M) at 25 ºC. Under these experimental conditions it is possible to relate the instantaneous intrinsic viscosity [η] with MV through the Mark-Houwink-Sakurada equation. Equations of Sano, Solomon-Ciuta, Deb-Chatterjee and Ram-Yaseen, which allow to compute values of [η] with a single measurement of relative (ηrel) and/or specific viscosity (ηsp), were employed to obtain instantaneous values of [η]. Instantaneous values of [η] were also obtained through an iterative process using Huggins equation. Initial velocity of depolymerization (vo) was obtained from different concentration of chitosan solutions and a fixed bromelain concentration. Michaelis-Menten constant (kM) and maximum velocity (Vm) were obtained using the Lineweaver-Burk representation of the Michaelis-Menten equation for each set of [η] which were calculated employing all procedures mentioned. Best kinetic parameters for chitosan depolymerization (kM=3.92x10-7 mol.dL-1; Vm=9.09x10-8 mol.dL-1.s-1) were obtained when Sano`s equation was employed to calculate [η] values.
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