In situ product removal via reactive extraction in itaconic acid fermentation with Ustilago cynodontis

Bio-based carboxylic acids are key platform chemicals for a circular economy, offering sustainable alternatives to fossil-derived products. Yet, high substrate and processing costs, along with narrow profit margins, restrict industrial-scale bioproduction. In situ product removal (ISPR) holds the potential to increase productivity and yield in fermentations by circumventing product inhibition. Thus, it presents a promising process intensification measure to bridge the commercial gap between bio-based and petrochemical platform chemicals. One effective method for product recovery is reactive extraction with trioctylamine. In the present study, this method was applied to itaconic acid (ITA) fermentations with Ustilago cynodontis. First, the successful operation of dispersion-based apparatuses for reactive extraction was proven using small-scale mixer-settlers, with 1-octanol and the biocompatible 2-octanone as diluents. We then developed an improved feeding profile, lowering byproduct formation by 72 %. Subsequently, we demonstrated the feasibility of ISPR using a perfusion bioreactor with an external membrane coupled to reactive extraction and back-extraction. After 233 h of fermentation, the total amount of ITA produced was increased by 26 %, and productivity was 21 % higher compared to extended-batch fermentations. However, the yield was only slightly improved by 5 %. Ultimately, we identified product toxicity far below the maximum titer of 80 g  ${\text{L}}^{-1}$ as a key bottleneck in ISPR fermentations with U. cynodontis. The results underscore the potential of ISPR and warrant further investigation in this field.