Regular articleProduction of sophorolipids from winterization oil cake by solid-state fermentation: Optimization, monitoring and effect of mixing

•Sophorolipids (SLs) are produced by solid-state fermentation (SSF) of organic wastes.•Starmerella bombicola grows on a mixture of winterization oil cake, molasses and straw.•S. bombicola produced 0.179 g of SL per g dry matter in 10 days.•Mixing at 3, 5 and 7 days increased SL production to 0.235 g per g dry matter.•SL yield correlates linearly with cumulative oxygen consumption.

Sophorolipids (SLs) are a group of extracellular biosurfactants produced by the yeast Starmerella bombicola. The present study explored the use of winterization oil cake (WOC), a residual oil cake that comes from the oil refining industry, as a substrate for the production of SLs by solid-state fermentation (SSF). Sugar beet molasses (MOL) was used as a co-substrate and S. bombicola ATCC 22214 as the inoculum. Fermentation was performed on the 100-g scale and was optimized in terms of the ratio of substrates and the aeration rate using response surface methodology. The optimized SSF process (1:4 MOL:WOC mass ratio and 0.30 L kg−1 min−1 aeration rate), carried out under static conditions, was monitored for 10 days with a maximum SL yield of 0.179 g per g DM (dry matter). The effect of intermittent mixing on the process was also investigated. Mixing caused a 31% increase in SL production, with a total yield of 0.235 g per g DM. The Oxygen Uptake Rate (OUR) and the Cumulative Oxygen Consumption (COC) were used to monitor the biological activity of the fermentation processes. There were significant correlations between the SL yield and the oxygen and fats consumed. The SLs were characterized by FTIR and 1H NMR analysis.

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