Scheffersomyces stipitis ability to valorize different residual biomasses for vitamin B₉ production

Sugar beet pulp (SBP), sugar beet molasses (SBM) and unfermented grape marcs (UGM) represent important waste in the agro-food sector. If suitably pre-treated, hexose and pentose sugars can be released in high quantities and can subsequently be used by appropriate cell factories as growth media and for the production of (complex) biomolecules, accomplishing the growing demand for products obtained from sustainable resources. One example is vitamin B₉ or folate, a B-complex vitamin currently produced by chemical synthesis, almost exclusively in the oxidized form of folic acid (FA). It is therefore desirable to develop novel competitive strategies for replacing its current fossil-based production with a sustainable bio-based process. In this study, we assessed the production of natural folate by the yeast Scheffersomyces stipitis, investigating SBM, SBP and UGM as potential growth media. Pre-treatment of SBM and SBP had previously been optimized in our laboratory; thus, here we focused only on UGM pre-treatment and hydrolysis strategies for the release of fermentable sugars. Then, we optimized the growth of S. stipitis on the three media formulated from those biomasses, working on inoculum pre-adaptation, oxygen availability and supplementation of necessary nutrients to support the microorganism. Folate production, measured with a microbiological assay, reached 188.2 ± 24.86 μg/L on SBM, 130.6 ± 1.34 μg/L on SBP and 101.9 ± 6.62 μg/L on UGM. Here, we demonstrate the flexibility of S. stipitis in utilizing different residual biomasses as growth media. Moreover, we assessed the production of folate from waste, and to the best of our knowledge, we obtained the highest production of folate from residual biomasses ever reported, providing the first indications for the future development of this microbial production process.