Kinetic analysis of two-phase enzymatic hydrolysis of hemicellulose of xylan type.

We present a coupled experimental and theoretical framework for quantifying the kinetics of two-phase enzymatic hydrolysis of hemicellulose. For xylan loading of 1-5mg/ml, the nature of inhibition by the product xylose (non-competitive), the kinetic constants (Km=3.93 mg/ml, Vmax=0.0252 mg/ml/min) and the xylose inhibition constant (Kx=0.122 mg/ml) are experimentally determined. Our multi-step two-phase kinetic model incorporating enzyme adsorption to the solid substrate and non-competitive product inhibition is simulated using our kinetic data and validated against our experimentally measured temporal dynamics of xylose and reducing sugars. Further experiments show that higher substrate loading reduces the specific adsorption of the endoxylanase to the solid xylan and the enzyme's solid-liquid distribution ratio, which decelerates the solid hydrolysis and accelerates the liquid phase reactions. Thus, the xylose yield increases with substrate loading, which increases product inhibition and decreases reducing sugar yields. An operating cost analysis gives 3mg/ml as the optimal substrate loading.
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