Medium Chain Carboxylic Acids from Complex Organic Feedstocks by Mixed Culture Fermentation

Abstract

Environmental pressures caused by population growth and consumerism require the development of resource recovery from waste, hence a circular economy approach. The production of chemicals and fuels from organic waste using mixed microbial cultures (MMC) has become promising. MMC use the synergy of bio-catalytic activities from different microorganisms to transform complex organic feedstock, such as by-products from food production and food waste. In the absence of oxygen, the feedstock can be converted into biogas through the established anaerobic digestion (AD) approach. The potential of MMC has shifted to production of intermediate AD compounds as precursors for renewable chemicals. A particular set of anaerobic pathways in MMC fermentation, known as chain elongation, can occur under specific conditions producing medium chain carboxylic acids (MCCAs) with higher value than biogas and broader applicability. This review introduces the chain elongation pathway and other bio-reactions occurring during MMC fermentation. We present an overview of the complex feedstocks used, and pinpoint the main operational parameters for MCCAs production such as temperature, pH, loading rates, inoculum, head space composition, and reactor design. The review evaluates the key findings of MCCA production using MMC, and concludes by identifying critical research targets to drive forward this promising technology as a valorisation method for complex organic waste.

Role of Microbial Hydrolysis in Anaerobic Digestion

“…Although most processes for SCCA utilization can be operated with the fermentation broth directly, some require the separation of SCCA from the media. This has been insufficiently tested and still poses a crucial challenge [98], however, separation of MCCA is easier due to their higher hydrophobicity [103].…”

Valorization of Vegetable Food Waste and By-Products Through Fermentation Processes

“…A wide range of bacterial and fungal species to treat several agricultural wastes have been reported in literature. Advances in microbial culture analysis and its integration with omics techniques will boost current understanding of mixed culture fermentation (De Groof et al, 2019) in order to design efficient fermentative processes for specific applications. The present work provides a classification of bacteria and fungi species and strains currently used for bioconversion of fruit and vegetable by-products, and a comparison of fermentative conditions needed to isolate specific functional compounds, or to achieve certain nutritional goals.…”

“…Recent examples of fermentation-based valorization strategies include anaerobic digestion of organic feedstocks through mixed culture fermentation (De Groof et al, 2019), fermentation of date palm waste to produce lactic acid as an alternative for the expensive raw material (Azam and Ahmad, 2019), bioconversion of cocoa by-products using bacteria, yeast or filamentous fungi to obtain enzymes, polysaccharides, beverages and nutraceuticals (Vásquez et al, 2019), and sourdough fermentation to elaborate baked foods that may ameliorate the symptoms of irritable bowel syndrome and release bioactive compounds related to the metabolism of phenolic compounds (Gobbetti et al, 2019). In general, most of the applications mentioned above use LAB to improve the nutritional value of several food matrices, or to isolate biologically active ingredients for functional food formulation.…”

“…In general, most of the applications mentioned above use LAB to improve the nutritional value of several food matrices, or to isolate biologically active ingredients for functional food formulation. Nevertheless, bioconversion processes and fermentation strategies to increase digestibility, enhance nutritional value and decrease the levels of antinutritional factors in these substrates using other types of bacteria, as well as different yeasts and molds, have been described (Chebaibi et al, 2019;De Groof et al, 2019;Lücke et al, 2019;Vásquez et al, 2019).…”

Lactate vs butyrate production during mixed culture glucose fermentation driven by substrate availability as determined by metaproteomics

“…Fermentation is a key central step in biologically treating organic waste in which waste carbon can be recycled into valuable short-chain fatty acids, alcohols, and other organic (bio)chemicals (Agler, Wrenn, Zinder, & Angenent, 2011;Angenent et al, 2016;De Groof, Coma, Arnot, Leak, & Lanham, 2019). While the definition is not universally agreed upon, fermentation can generally be described as biological catabolism without the use of an external electron acceptor (such as O 2 , NO 3 -, or SO 4 2-), and commonly relies on substratecoupled electron transfer reactions for energy generation (El-Mansi, Bryce, Demain, & Allman, 2006).…”