In this study a bioink containing the horseradish peroxidase (HRP) enzyme was formulated and jetted with a piezoelectric‐based ink‐jet deposition system. A number of polymers with different molecular weights, functional groups and electric charge were tested as viscosity modifiers. The impact of viscosity modifiers on HRP activity was systematically studied. It was found that viscosity modifiers typically used in commercial ink formulations significantly impaired HRP activity possibly due to limitations in diffusion. In contrast, carboxymethyl cellulose increased viscosity to the desired range for piezoelectric jetting without negatively affecting the HRP activity. Good jettability was obtained for the HRP bioink by adding a suitable surfactant, a viscosity modifier and a humectant.magnified image
Enzymatic hydrolysis at high solids loadings is key to scale-up of lignocellulosic biochemical conversion processes, because of potentially higher sugar and ethanol titers and lower hydraulic loads. However, high solids loadings can pose rheological challenges, reduce mass and heat transfer effi ciency, and increase the concentration of enzyme inhibitors in the system, resulting in low conversion of glucan and xylan into fermentable sugars. In this study, ten batch enzymatic hydrolyses were conducted in a 200-liter reactor, while monitoring sugar and inhibitor profi les.The effects of enzyme cocktail, biomass loading, pre-treatment severity, and hydrolysis temperature were assessed using techno-economic indicators to evaluate the effi cacy of the enzymatic hydrolysis. For similar experimental conditions, different enzyme cocktails produced distinct hydrolysis outcomes allowing cocktail optimization. In spite of a rapid initial reaction rate, fermentable sugars concentrations reached a plateau after about 48 h, indicating severe inhibition. Increased biomass loadings did not proportionally increase sugar production. Both observations indicated the presence of severe inhibition, likely endogenous. Pre-treatment at a lower severity (200 o C for 8 min) led to the most effi cient hydrolysis, while higher severities destroyed hemicellulose and led to lower overall sugar production.Lower saccharifi cation temperatures (30-32°C) caused a 20% decrease in sugar conversion when compared to 50°C operation. Strategies to mitigate inhibition will be required if high-solids enzyme hydrolysis is to be successfully scaled up to commercially relevant levels.
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