**5. Conclusions**

In the present work, hexose- and pentose-rich streams after organosolv pretreatment and fractionation of wheat straw with ACO and EtOH were used as carbon sources for *C. cohnii* cells for the production of fatty acids and, more specifically, DHA. Enzymatic hydrolysates from solid fractions have shown great potential, achieving up to 70.3 wt.% TFA accumulation and 32.2% DHA of total lipids. Pentose-rich liquid fractions resulted in lower DHA yield (up to 13%), indicating the presence of compounds in the hydrolysate that may affect the lipid synthesis and alter the fatty acids profile. Moreover, the type of carbon source affects not only the amount of lipids but also the relative proportion of DHA that is accumulated in the cells. It is worth mentioning that this is the first report demonstrating, as a proof of concept, the valorization of all sugar streams towards the production of omega-3 fatty acids. Despite the challenges of the liquid fraction utilization, the suggested process is a promising approach towards the production of omega-3 fatty acids from non-edible sources and opens up new routes, considering the availability of wheat straw residues that are made available from the Greek agricultural sector, as well as worldwide.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/fermentation7040219/s1, Figure S1: Time course of growth of *C. cohnii* cells on enzymatic hydrolysate from solid pulps as carbon source, Table S1: Concentration of phenolic compounds in the liquid fraction before and after detoxification, Table S2: Total reducing sugars released after enzymatic hydrolysis of solid fraction, Table S3. Initial sugar concentration and consumption after 120 h of fermentation of *C. cohnii*.

**Author Contributions:** Conceptualization, A.K. and K.G.K.; methodology, G.A., A.K., S.S., K.G.K. and S.D.S.; validation, G.A., A.K. and S.D.S.; formal analysis, G.A., A.K., S.S. and S.D.S.; investigation, G.A., S.S. and S.D.S.; resources, A.A.L. and E.T.; data curation, G.A., A.K. and S.D.S.; writing original draft preparation, G.A., S.S., A.K. and S.D.S.; writing—review and editing, A.K. and S.D.S.; visualization, A.K. and S.D.S.; supervision, A.K., A.A.L. and E.T.; project administration, A.K., A.A.L. and E.T.; funding acquisition, K.G.K., A.A.L. and E.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research was financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH—CREATE—INNOVATE (project code: T2EDK-00468). G. Asimakopoulou would like to thank the State Scholarship Foundation (IKY) of Greece for providing a PhD fellowship (NSRF 2014–2020) through the program "Development of human resources, education and lifelong learning".

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
