Direct Conversion of Food Waste Extract into Caproate: Metagenomics Assessment of Chain Elongation Process

Abstract

In a circular economy strategy, waste resources can be used for the biological production of high added-value substances, such as medium chain fatty acids (MCFAs), thus minimising waste and favouring a sustainable process. This study investigates single-stage fermentation processes for the production of MCFAs in a semi-continuous reactor treating the extract of real food waste (FW), without the addition of external electron donors. Two sequential acidogenic fermentation tests were carried out at an organic loading rate (OLR) of 5 and 15 gCOD L−1d−1 with a hydraulic retention time of 4 days and pH controlled at 6 ± 0.2. The highest level of caproate (4.8 g L−1) was observed at OLR of 15 gCOD L−1d−1 with a microbiome mainly composed by lactate-producing Actinomyces, Atopobium, and Olsenella species and caproate-producing Pseudoramibacter. Metagenomic analysis revealed the presence of key enzymes for the production of lactate, such as lactate dehydrogenase and pyruvate ferredoxin oxidoreductase, as well as several enzymes involved in the reverse β-oxidation pathway, thus suggesting the occurrence of a lactate-based chain elongation process.

Short Chain Fatty Acids and Bacterial Taxa Associated with Reduced Salmonella enterica serovar I 4,[5],12:i:- Shedding in Swine Fed a Diet Supplemented with Resistant Potato Starch

“…These two longer SCFAs may be indicators of conditions that favor bacteria which are fermentative specialists. It has been proposed that longer SCFAs can be produced using propionate or butyrate as substrates, with the same metabolic machinery as used in butyrate production in a reverse beta-oxidation process ( 31 ). It follows that valerate and caproate may only be produced once conditions that favor fermentative specialists are established and shorter SCFAs such as acetate, propionate, and butyrate are abundant.…”

Impact of Dietary Isoflavone Supplementation on the Fecal Microbiota and Its Metabolites in Postmenopausal Women

“…The current data reveal an increase in CA production after isoflavone supplementation, which indicates differential microbial activity leading to the production of this compound. CA derives from chain elongation reactions in which SCFAs are converted to MCFAs mainly using ethanol or lactate as an electron donor [50]. The elongation process is mediated by microorganisms through the reverse β-oxidation pathway.…”

The Application of Metagenomics to Study Microbial Communities and Develop Desirable Traits in Fermented Foods

“…For this, the technologies of metagenomics, synthetic biology and microbial biotransformation can be employed. Metagenomics allows researchers to first identify microbial genes linked to the production of useful enzymes or value-added compounds [ 269 , 270 , 271 , 272 ]. Synthetic biology techniques would then enable the commercial application of these pathways by improving efficiency and allowing upscaling [ 269 , 270 , 271 , 272 ].…”