Statistical optimization and scaled-up bioreactor fermentation for enhanced edible oil production from palm date waste by Rhodotorula glutinis KAEC-61

Agro-industrial residues such as palm date waste (PDW) represent an abundant and underutilized carbon source with significant potential for microbial valorization. Oleaginous yeasts, known for their high lipid-accumulating capacity, offer a sustainable route for single-cell oil (SCO) production, particularly in arid regions where PDW is prevalent. However, the efficient bio-conversion of such lignocellulosic feedstocks requires robust microbial strains and optimized fermentation strategies. In this study, an isolated strain of Rhodotorula glutinis KAEC-61 from mangrove sediments was selected from several isolates for its superior lipid-producing ability. Initial flask-level screening under non-optimized conditions yielded 1.9 ± 0.10 g/L biomass and 0.56 ± 0.06 g/L lipid titer (29% lipid content). Optimization via the one-variable-at-a-time (OVAT) method increased biomass and lipid production by 4.4-fold and 6-fold, respectively, reaching 8.42 ± 0.52 g/L biomass and 3.37 ± 0.55 g/L lipid titer (40% lipid content). Further enhancement through Plackett-Burman and Box-Behnken designs led to 11-fold and 16.7-fold improvements, achieving 20.95 ± 1.2 g/L biomass and 9.35 ± 0.35 g/L lipid titer (44.6% lipid content) from 53.7 ± 0.29 g/L xylose in a 7-L bioreactor under controlled pH. A fed-batch fermentation strategy further elevated performance to 27.0 ± 1.08 g/L biomass and 13.0 ± 0.36 g/L lipid titer (48.1% lipid content). When xylose was replaced with PDW hydrolysate, lipid production increased to 14.7 ± 1.14 g/L titer (54.4% lipid content), representing a 26.3-fold improvement over initial conditions. Fatty acid profiling revealed a composition dominated by oleic and linoleic acids, with over 54% comprising unsaturated fatty acids. Notably, γ-linolenic acid, cis-10-pentadecenoic acid, and cis-11-eicosenoic acid rare fatty acids with distinct physicochemical and nutraceutical properties were detected, highlighting the strain's potential for specialty lipid production. This study establishes a scalable, statistically optimized bioprocess for PDW valorization using an environmental isolate of R. glutinis, contributing to circular bioeconomy strategies for sustainable microbial lipid biomanufacturing.