Iris Cornet

Grease trap waste (GTW) is a lipid-rich, low-value waste stream that is a promising feedstock for the production of long-chain dicarboxylic acids (LCDAs) by Candida viswanathii. However, the presence of anionic surfactants and trace metals hinders this bioconversion process. This study evaluated the use of ceramic ultrafiltration as a pretreatment technology. A 3 nm ZrO₂ ceramic membrane removed approximately 90% of anionic surfactants and over 90% of Ni, Zn and Fe. Using a C1-grafted variant increased the flux sevenfold, to 2.3 L/(m².h), while retaining the same level of removal. Pretreating the GTW increased LCDA titres in shake flasks by up to sixfold compared to untreated feed. In fed-batch bioreactor runs, pretreated GTW yielded 43.5 g/L LCDA, which is a 25% improvement to the untreated GTW, with a final productivity of 0.46 g/(L.h) and a lipid-to-LCDA yield of 82%. However, biomass formation was lower with pretreated GTW, likely reflecting reduced levels of growth-promoting cofactors. Nevertheless, these results demonstrate that ceramic ultrafiltration enables robust LCDA production from GTW, supporting valorisation of lipid wastes.

Efficient recovery of long-chain dicarboxylic acids (LCDAs) from aqueous fermentation broths is a key challenge for the industrial development of bio-based LCDA production. This study evaluates liquid–liquid extraction (LLE) as a downstream recovery strategy, comparing physical extraction (PE) and reactive extraction (RE) for DCA 12, DCA 16, and DCA 18. The novelty of this work lies in demonstrating that LCDA extraction is governed by mechanisms fundamentally different from those of short- and medium-chain dicarboxylic acids. Whereas shorter chain dicarboxylic acids are mainly controlled by dissociation degree, LCDA recovery is strongly influenced by carbon-chain apolarity, low aqueous solubility, and compound losses through agglomeration, precipitation, and/or micellization. PEs enabled the selective recovery of the more hydrophobic DCA 16 and DCA 18 over DCA 12, confirming the dominant role of chain length in LCDA separation. In contrast, RE with Aliquat^®336 maximized total LCDA recovery, achieving extraction efficiencies above 85%, but with reduced selectivity. Validation in autoclaved fermentation broth from UCO feedstock confirmed the potential of Aliquat^®336 in octanol for high LCDA recovery, while revealing lower extraction efficiencies than in model mixtures due to broth matrix complexity. Overall, this study establishes LLE as a promising platform for LCDA recovery and highlights that future downstream process design must balance total recovery, chain-length selectivity, and broth-specific matrix effects.

Rhodococcus opacus is an oleaginous actinobacterium with considerable potential for lipid-based bioproduction, as well as for utilising a variety of carbon sources as substrates, including renewable, cost-effective resources. Although its capacity for triacylglycerol accumulation is well established, the regulatory logic that governs its fatty acid and mycolic acid biosynthesis is still poorly understood. Here, we investigated the transcriptional control of the type II fatty acid synthase (FASII) pathway in R. opacus PD630, revealing a regulatory architecture that is more complex than previously assumed. Differential gene expression analysis showed that environmental cues, including temperature, pH, carbon-to-nitrogen ratio and the presence of free fatty acids influence the FASII gene cluster expression in a non-uniform manner. This phenomenon suggests the presence of internal transcription start sites and modular regulation within the cluster. We identified three lipid-responsive transcription factors, MabR _RO , FadR1 _RO and FadR2 _RO , that are all capable of binding the fasII promoter in vitro . DNA binding of FadR1 _RO and FadR2 _RO was disrupted by long-chain acyl-CoA molecules, indicating ligand-dependent control. Together, these findings reveal previously unrecognised layers of transcriptional regulation in the R. opacus FASII pathway and highlight both conserved and divergent regulatory features within the Mycobacteriales lineage. Featured Image:

The enzymatic synthesis of esterified flavors is pivotal in the food, pharmaceutical, and cosmetic industries. Among the available approaches, lipase-catalyzed reactions have gained increasing attention due to the enzymes' biodegradability, high enantio- and regioselectivity, availability, and effectiveness under mild, eco-friendly conditions, aligning well with the principles of green chemistry. This topic was selected due to the vast potential of biocatalysis in the sustainable and efficient synthesis of diverse flavor compounds. Using the Web of Science database with the keywords "flavor", "enzyme", and "lipase", 189 relevant articles were identified, revealing that the majority of publications fall within the fields of chemistry, food science, and biochemistry. This review explores the catalytic mechanisms of lipases during acetylation reactions, focusing on structural conformational changes during enzymatic processes. Lipases from Candida antarctica (notably CALB, Lipozyme, and Novozym 435) emerge as the most commonly employed biocatalysts for esterified flavor production. Interestingly, most studies emphasize the immobilization supports rather than the intrinsic properties or engineering of the enzymes themselves. The findings underscore a growing global interest in enzyme-mediated flavor synthesis. Future studies should explore enzyme engineering to enhance activity and specificity, broaden the range of usable substrates, and improve the operational stability. Key challenges include the high cost of enzyme production, limited substrate scope in some systems, and the need for scalable, cost-effective bioprocesses for industrial applications.