Search

The establishment of a sustainable circular bioeconomy requires the effective material recycling from biomass and biowaste beyond composting/fertilizer or anaerobic digestion/bioenergy. Recently, volatile fatty acids attracted much attention due to their potential application as carbon source for the microbial production of high added-value products. Their low-cost production from different types of wastes through dark fermentation is a key aspect, which will potentially lead to the sustainable production of fuels, materials or chemicals, while diminishing the waste volume. This article reviews the utilization of a volatile fatty acid platform for the microbial production of polyhydroxyalkanoates, single cell oil and omega-3 fatty acids, giving emphasis on the fermentation challenges for the efficient implementation of the bioprocess and how they were addressed. These challenges were addressed through a research project funded by the European Commission under the Horizon 2020 programme entitled 'VOLATILE-Biowaste derived volatile fatty acid platform for biopolymers, bioactive compounds and chemical building blocks'., This work was supported by the European project 'Volatile-Biowaste-derived volatile fatty acid platform for biopolymers, bioactive compounds and chemical building blocks' and has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 720777.

The market for pectinolytic enzymes is continually expanding. In addition to the food, animal feed, textile and paper industries, pectinases have recently found application in the field of biorefinery. However, the industrial production of these enzymes is associated with high costs. Thus, the search for new source of microbial enzymes with low culture requirements, or from new substrates that allow the development of cost-effective and ecofriendly processes is of utmost importance. In this study, an unusual microbial source was postulated to produce pectinases from an uncommon agro-waste substrate. This study is the first report that reveals the production of pectinases by Crypthecodinium cohnii using as culture media liquors obtained after organosolv pretreatment of exhausted olive pomace (EOP). Results showed that using EOP as substrate, this strain was able to produce 42.15 ± 0.41 U/mL of extracellular polygalacturonase. Additionally, the valorization of EOP as a substrate to produce pectinases can be enhanced through the extraction of lipids rich in omega-3, making it a cost-effective and zero-waste process.

Crypthecodinium cohnii represents a heterotrophic microalga rich in omega-3 polyunsaturated fatty acids (PUFAs) with significant health benefits, and especially docosahexaenoic acid (DHA). In the present study, freeze-dried C. cohnii biomass, cultivated in fed-batch bioreactors with a feed of acetic acid 33% (v/v), was used. In the first set of experiments, ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE) were employed with the aim of discovering the most efficient technique regarding the recovery of DHA. Organic and food grade solvents were used, namely n-hexane, 2-2-butanol and n-hexane: isopropanol (2:3), under specific conditions. Extraction yields (EYs) were calculated and PUFAs content was evaluated through Gas Chromatography (GC). UAE using n-hexane: isopropanol (2:3) and 2-butanol presented the highest yields and were further examined in the second set of experiments in order to optimize the recovery of DHA, while changing the extraction time and the ultrasound power. Enzymatic Hydrolysis (EH) was also applied using four enzyme preparations, three concentrations of C. cohnii biomass and n-hexane: isopropanol (2:3) as solvent. In addition, homogenisation assisted extraction in microemulsion (HAE) was studied while changing the solvent, time and rotation speed. Simple mathematical models were applied in order to correlate the EY with the applied conditions for every extraction method. Parameters screening during UAE demonstrated that the best extraction time was 15 min, reaching the yield of 26.17% and total fatty acids (TFAs) content of 261.75 mg/g dry weight (DW). Among all used extraction techniques, UAE recovered maximum quantities of TFAs, while HAE was proven the most efficient regarding DHA content (131.20 mg/g DW). In conclusion, the proposed green extraction methods were found to be attractive for the recovery of PUFAs from C. cohnii.

Omega-3 fatty acids have become a commodity of high nutritional and commercial value; intensive fishing and its environmental and social cost has led researchers to seeking alternative more sustainable ways of producing them. Heterotrophic microalgae such as Crypthecodinium cohnii, a marine dinoflagellate, have the ability to utilize various substrates and accumulate high amounts of docosahexaenoic acid (DHA). In this work, a mild oxidative organosolv pretreatment of beechwood pulps was employed that allowed up to 95% of lignin removal in a single stage, thus yielding a cellulose-rich solid fraction. The enzymatic hydrolysates were evaluated for their ability to support the growth and lipid accumulation of C. cohnii in batch and fed-batch cultures; the results verified the successful microalgae growth, while DHA reached up to 43.5% of the cell’s total lipids. The proposed bioprocess demonstrated the utilization of non-edible biomass towards high added value food supplements in a sustainable and efficient manner.

Dark fermentation is an anaerobic digestion process of biowaste, used to produce hydrogen- for generation of energy- that however releases high amounts of polluting volatile fatty acids, such as acetic acid, in the en- vironment. In order for this biohydrogen production process to become more competitive, the volatile fatty acids stream can be utilized through conversion to high added-value metabolites, such as omega-3 fatty acids. The docosahexaenoic acid is one of the two most known omega-3 fatty acids and has been found to be necessary for a healthy brain and proper cardiovascular function. The main source is currentlyfish, which obtain the fatty acid from the primary producers, microalgae, through the food chain.Crypthecodinium cohnii, a heterotrophic marine microalga, is known for accumulating high amounts of docosahexaenoic acid, while offering the advantage of assimilating various carbon sources, such as glucose, ethanol, glycerol and acetic acid. The purpose of this work was to examine the ability of aC. cohniistrain to grow on different volatile fatty acids, as well as, on a pretreated dark fermentation effluent and accumulate omega-3. The strain was found to grow well on relatively high concentrations of acetic, butyric or propionic acid as main carbon source in a fed-batch pH-auxostat. Most importantly,C. cohniitotally depleted the organic acid content of an ultra-filtrated dark fermentation effluent after 60 h of fed-batch cultivation, therefore offering a bioprocess not only able to mitigate environmental pollutants, but also to provide a solution for a sustainable energy production process. The accumulated doc- osahexaenoic acid content was as high as 29.8% (w/w) of total fatty acids.

Volatile Fatty Acids (VFA) are small organic compounds that have attracted much attention lately, due to their use as a carbon source for microorganisms involved in the production of bioactive compounds, biodegradable materials and energy. Low cost production of VFA from different types of waste streams can occur via dark fermentation, offering a promising approach for the production of biofuels and biochemicals with simultaneous reduction of waste volume. VFA can be subsequently utilized in fermentation processes and efficiently transformed into bioactive compounds that can be used in the food and nutraceutical industry for the development of functional foods with scientifically sustained claims. Microalgae are oleaginous microorganisms that are able to grow in heterotrophic cultures supported by VFA as a carbon source and accumulate high amounts of valuable products, such as omega-3 fatty acids and exopolysaccharides. This article reviews the different types of waste streams in concert with their potential to produce VFA, the possible factors that affect the VFA production process and the utilization of the resulting VFA in microalgae fermentation processes. The biology of VFA utilization, the potential products and the downstream processes are discussed in detail. VOLATILE, a project funded by the European Union’s Horizon 2020 research and innovation program, under the grant agreement no. 720777. The Greek State Scholarships (Postdoc-Research Scholarships IKY). The Hellenic Foundation of Research and Innovation (ELIDEK) financial support (ELIDEK Scholarships for Ph.D. Students).