Isolation and identification of oleogenic yeasts from milk and dairy products and optimisation of single-cell oil production conditions

In this study, 112 strains isolated from milk, yoghurt, cheese, butter, ayran, clotted cream, and whey were identified as oleaginous. Twelve isolates with high dry biomass yields (0.4–0.7 g) were selected for single cell oil (SCO) production, and the fatty acid profiles of the produced lipids were determined. The genetic characterisation of isolates A2-1, A2-3, and Y20-6 selected based on dry biomass yield, lipid content, and unsaturated fatty acid composition, was performed. SCO production was carried out using strain A2-1, isolated from a yoghurt sample, which exhibited high biomass yield, SCO content, and total unsaturated fatty acid content. This strain was selected from among three isolates identified as Clavispora lusitaniae , and biochar derived from walnut shells was added to the production medium. Optimal conditions for dry biomass yield, lipid content, and fatty acid composition of SCO were achieved using biochar concentrations of 5–10 g/L and of 96–144 hour incubation. The optimal biochar concentration and incubation time for maximising SCO yield were 9.40 g/L and 127.2 h, respectively. Under these conditions, the dry biomass yield was 1.42 g, the lipid content was 2.12%, and the total unsaturated fatty acid content was 55.46% in the produced SCO. Moreover, γ-linolenic acid (C18:3, n-6) and arachidonic acid (C20:4, n-6) (ARA) were detected in the SCOs produced under optimal conditions.