Kinetic Characterization of Enzymatic Hydrolysis of Apple Pomace as Feedstock for a Sugar-Based Biorefinery

Alessandra Procentese,Antonio Marzocchella,Ilaria Di Somma,Maria Elena Russo

doi:10.3390/en13051051

Alessandra Procentese, Antonio Marzocchella + Show 2 more

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https://doi.org/10.3390/en13051051

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Abstract

The enzymatic hydrolysis of cellulose from biomass feedstock in the sugar-based biorefinery chain is penalized by enzyme cost and difficulty to approach the theoretical maximum cellulose conversion degree. As a consequence, the process is currently investigated to identify the best operating conditions with reference to each biomass feedstock. The present work reports an investigation regarding the enzymatic hydrolysis of apple pomace (AP). AP is an agro-food waste largely available in Europe that might be exploited as a sugar source for biorefinery purposes. A biomass pre-treatment step was required before the enzymatic hydrolysis to make available polysaccharides chains to the biocatalyst. The AP samples were pre-treated through alkaline (NaOH), acid (HCl), and enzymatic (laccase) delignification processes to investigate the effect of lignin content and polysaccharides composition on enzymatic hydrolysis. Enzymatic hydrolysis tests were carried out using a commercial cocktail (Cellic®CTec2) of cellulolytic enzymes. The effect of mixing speed and biomass concentration on the experimental overall glucose production rate was assessed. The characterization of the glucose production rate by the assessment of pseudo-homogeneous kinetic models was proposed. Data were analysed to assess kinetic parameters of pseudo-mechanistic models able to describe the glucose production rate during AP enzymatic hydrolysis. In particular, pseudo-homogeneous Michaelis and Menten, as well as Chrastil’s models were used. The effect of lignin content on the enzymatic hydrolysis rate was evaluated. Chrastil’s model provided the best description of the glucose production rate.

Highlights

The conversion of lignocellulosic biomass into bio-based chemicals according to the biorefinery sugar-platform involves four main steps: (i) pre-treatment to remove/disaggregate the lignin structure;(ii) enzymatic hydrolysis to convert polysaccharides into fermentable sugars; (iii) fermentation to convert sugars into bio-based products; and (iv) recovery and concentration of the bio-based products [1].The enzymatic conversion of cellulose into fermentable sugars is one of the bottlenecks of the whole biorefinery chain
Raw and pre-treated apple pomace (AP) samples were characterized in term of cellulose, hemicellulose, and lignin content according to the polysaccharides quantification assay [17] as well as in terms of biomass recovery after each delignification pre-treatment
A procedure for the assessment of the overall kinetics of glucose production from apple pomace enzymatic hydrolysis catalysed by cellulase cocktails was applied using a commercial enzyme cocktail (Cellic® CTec2)

Summary

Introduction

The conversion of lignocellulosic biomass into bio-based chemicals according to the biorefinery sugar-platform involves four main steps: (i) pre-treatment to remove/disaggregate the lignin structure;(ii) enzymatic hydrolysis to convert polysaccharides into fermentable sugars; (iii) fermentation to convert sugars into bio-based products; and (iv) recovery and concentration of the bio-based products [1].The enzymatic conversion of cellulose into fermentable sugars is one of the bottlenecks of the whole biorefinery chain. The conversion of lignocellulosic biomass into bio-based chemicals according to the biorefinery sugar-platform involves four main steps: (i) pre-treatment to remove/disaggregate the lignin structure;. The success of this step depends strongly on the operating conditions (e.g., temperature, pH, biomass/liquid ratio, enzyme loading), the effect of product inhibition on enzyme catalysis [2], and the enzyme consumption (specific activity, stability, enzyme recycling strategies). These issues affect the overall production cost of the sugars. The first pre-treatment aimed at delignification strongly affects the rate and the degree of conversion of the enzymatic hydrolysis of polysaccharides. The nature of the pre-treatment (steam explosion, chemical pre-treatment with acid or alkaline solvents, organosolv, biological, etc.) influence the composition and the structure of the biomass substrate subjected to the enzymatic hydrolysis [4,5]

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