Valorization of Crude Glycerol, Residue Deriving from Biodiesel- Production Process, with the Use of Wild-type New Isolated Yarrowia lipolytica Strains: Production of Metabolites with Pharmaceutical and Biotechnological Interest.

BACKGROUND & OBJECTIVE: Crude glycerol (Glol), used as substrate for screening eleven natural Yarrowia lipolytica strains in shake-flask experiments. Aim of this study was to assess the ability of the screened strains to produce biomass (dry cell weight; X), lipid (L), citric acid (Cit), mannitol (Man), arabitol (Ara) and erythritol (Ery), compounds presenting pharmaceutical and biotechnological interest, in glycerol-based nitrogen-limited media, in which initial glycerol concentration had been adjusted to 40 g/L.

METHODS: Citric acid may find use in biomedical engineering (i.e. drug delivery, tissue engineering, bioimaging, orthopedics, medical device coating, wound dressings). Polyols are considered as compounds with non-cariogenic and less calorigenic properties as also with low insulin-mediated response. Microbial lipids containing polyunsaturated fatty acids (PUFA) are medically and dietetically important (selective pharmaceutical and anticancer properties, aid fetal brain development, the sight function of the eye, hormonal balance and the cardio-vascular system, prevent reasons leading to type-2 diabetes, present healing and anti-inflammatory effects).

RESULTS: All strains presented satisfactory microbial growth (Xmax=5.34-6.26 g/L) and almost complete substrate uptake. The principal metabolic product was citric acid (Citmax=8.5-31.7 g/L). Production of cellular lipid reached the values of 0.33-0.84 g/L. Polyols were also synthesized as strain dependent compounds (Manmax=2.8-6.1 g/L, Aramax ~2.0 g/L, Erymax= 0.5-3.8 g/L). The selected Y. lipolytica strain ACA-DC 5029 presented satisfactory growth along with synthesis of citric acid and polyols, thus, was further grown on media presenting an increased concentration of Glol~75 g/L. Biomass, lipid and citric acid production presented significant enhancement (Xmax=11.80 g/L, Lmax=1.26 g/L, Citmax=30.8 g/L), but conversion yield of citric acid produced per glycerol consumed was decreased compared to screening trials. Erythritol secretion (Erymax=15.6 g/L) was highly favored, suggesting a shift of yeast metabolism from citric acid accumulation towards erythritol production. Maximum endopolysaccharides (IPS) concentration was 4.04 g/L with yield in dry weight 34.2 % w/w.

CONCLUSION: Y. lipolytica strain ACA-YC 5029 can be considered as a satisfactory candidate grown in high concentrations of crude glycerol to produce added-value compounds that interest pharmaceutical and biotechnology industries.