Simultaneous and Hybrid Saccharification-Fermentation of Agavin Derived from Agave Leaves Using rInu-ISO3 Inulinase and Cupriavidus necator H16 for an Efficient Polyhydroxybutyrate Production

Abstract

Agave residues from the tequila industry contain branched inulin (agavin), and this structure limits its efficient utilization. Hence, inulin hydrolysis has been proposed as a strategy for valorizing agave residues. This contribution describes the utilization of recombinant inulinase (rInu-ISO3), an enzyme, to degrade agavin derived from agave residues. The hydrolysis products are used by Cupriavidus necator H16 to simultaneously produce polyhydroxybutyrate (PHB). Within this approach and in line with process intensification principles to increase energy and cost efficiency, two strategies were assessed for the saccharification and fermentation stages, namely, Simultaneous Saccharification and Fermentation (SSF) and Hybrid Hydrolysis and Fermentation (HHF). A maximum biomass titter of 6.5 g L^–1 with a PHB accumulation of 58 wt % was achieved after 5 min of hydrolysis reaction using an HHF strategy, whereas the SSF method yielded 5.1 g L^–1 of biomass with a polymer content of 55 wt %. The obtained materials were characterized by using proton nuclear magnetic resonance (¹H NMR) and size exclusion chromatography (SEC), which confirms the presence of PHB with a number-average molar mass (M_n) of 537 kDa and a dispersity (D̵) value of 2.4. In comparison with similar reported systems focusing on the valorization of inulin, the results of these current research efforts may represent a milestone to demonstrate the feasibility of using the rInu-ISO3 enzyme to produce chemicals of added value from waste biomass while offering an alternative to alleviate the ongoing environmental crisis derived from petroleum.

Agavin, a complex carbohydrate, is hydrolyzed with an in-house enzyme, rInu-ISO3, to produce bioplastics. This process provides a sustainable alternative to petroleum-based plastics, while valorizing agave residues and contributing to reduced environmental pollution.