Biomass demineralization and pretreatment strategies to reduce inhibitor concentrations in itaconic acid fermentation by Aspergillus terreus

Authors: Kennedy, Gregory - Greg; Bowman, Michael; Ascherl, Kim; Nichols, Nancy; SAHA, BADAL - Retired ARS Employee

Submitted to: Biomass
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Itaconic acid is a building block platform chemical that is produced industrially from glucose by fermentation with a fungus. Compared to use of glucose as feedstock, agricultural residues have the potential to serve as a lower-cost source of sugars for itaconic acid production. However, the fungus could not produce itaconic acid from the sugars obtained using standard methods to break down wheat straw. This type of sugar source is a complex mixture that contains variable concentrations of elements (in particular, trace metals) that have been previously shown to inhibit itaconic acid production and generally must be removed using multistep mitigations. Sources of these various inhibitory elements in the process for sugar release from wheat straw have been determined. A method for minimizing the inhibitory elements was identified and itaconic acid production from unmitigated wheat straw sugars was then demonstrated. The results will provide direction for process development to allow production of itaconic acid using agricultural residues.

Technical Abstract: Itaconic acid (IA) is a platform chemical, derived from non-petroleum sources, produced through fermentation of glucose by Aspergillus terreus. However, producing IA from alternative sugar sources (e.g. lignocellulose) has been shown to be problematic, requiring post-hydrolysis mitigation to allow growth and IA production by the fungus. It is well known that side products of lignocellulosic biomass conversion to sugars act as microbial growth inhibitors. An uncommon feature of fungal organic acid fermentations is production inhibition caused by mineral ions in biomass hydrolysate after pretreatment and enzymatic hydrolysis. To minimize mineral introduction during pretreatment and hydrolysis, we determined sources of growth and production inhibitors at each of these steps. Biomass demineralization and four pretreatment strategies were evaluated for inhibitor introduction. Dilution assays determined the approximate degree of inhibition for each hydrolysate. Ammonium hydroxide pretreatment of demineralized wheat straw presented the lowest concentration of inhibitors and concomitant lowest inhibition: subsequent fermentations produced 35 g L-1 IA from wheat straw hydrolysate (91 g L-1 sugar) without post-hydrolysis mitigation.