Augmented lipid biosynthesis in native fungus through dual-stage optimization of lignocellulosic biomass residue pretreatment and fermentation conditions

While lignocelluloses have seen significant use in a variety of commercial industries in recent years, they also play an important role in the circular bioeconomy. Alternatively, microbial oils surpass bioethanol and biobutanol in energy density, feedstock versatility, and sustainability, making them a superior biodiesel precursor. As a result, this study aimed to produce microbial oil to enhance the sustainability of biodiesel manufacturing. The focus was on the efficient valorization of de-oiled Pongamia seed cake, a byproduct of second-generation biodiesel production, by using a two-stage optimization process to increase Aspergillus ochraceus fungal oil yield. The first stage involved statistical optimization of dilute sulfuric acid (H₂SO₄) pretreatment conditions, specifically acid concentration, cake concentration, and pretreatment time, and the optimized conditions favoring maximum fermentation sugar release were determined as 3.25% (v/v) acid, 8.25% (w/v) cake, and 76 min pretreatment time. The second stage involved optimizing microbial synthesis process parameters, with a 12-day incubation period, 12% (v/v) inoculum, 30 °C temperature, and a culture medium pH of 6.0 being determined as optimal. This two-stage process optimization strategy boosted the biomass, lipid, and lipid % in A. ochraceus to 22.69 ± 1.82 g/L, 5.02 ± 0.77 g/L, and 22.12 ± 0.32%, respectively.