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 C. 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), which corresponds to 19.1 g per 100 g of substrates (sum of the initial wet mass of WOC and MOL in the reactor). 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, which corresponds to 25.1 g per 100 g of substrates. 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 1 H-NMR analysis.

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In this manuscript, we approach the production of biosurfactants as a cleaner alternative to the chemically-produced surfactants currently used in a wide range of industries. Sophorolipids are microbially produced biosurfactants of the glycolipid type that have entered the market in select applications such as detergent or cosmetic formulation ingredients. This study focuses on sophorolipid production by the yeast Starmerella bombicola from stearic acid (C18:0), a low-cost carbon source that is difficult to work with in submerged fermentation since it remains a solid due to its high melting temperature. Consequently, optimizations of solidstate fermentation inoculated with Starmerella bombicola were studied for conversions of stearic acid and molasses to sophorolipids. Polyurethane foam functioned as the inert support. The effect of polyurethane foam density and water holding capacity was assessed and the process was optimized in terms of substrate and inoculum ratio. The best conditions were: foam with a density of 32 kg m-3 at 75% water holding capacity, 1.17:1 molasses/stearic acid (w/w) and 5% (v/w) inoculum, to obtain a yield of 0.211 g sophorolipids per g of substrates. Mass spectrometry revealed that the sophorolipids produced herein had high concentrations of diacetylated acidic and lactonic C18:0 forms. The results of interfacial properties studies revealed that C18:0 sophorolipids had promising surface tension lowering capacity and emulsification behavior. This study describes a new strategy to produce biosurfactants using low environmental impact technologies as an alternative to traditional ways to produce chemical detergents.

Sophorolipids (SL) are microbial biosurfactants that have entered the market as detergent and cosmetic formulation ingredients. Current research is focused on the use of wastes to decrease the final production costs of SL and the environmental impacts. SL from wastes will help to move toward the circular economy only if the SL produced this way are pure enough and as efficient as current commercial SL. This manuscript focuses on the study of the structures and the interfacial properties of a crude SL natural mixture produced by solid‐state fermentation from a residual sunflower oil cake from the oil‐refining industry. Liquid chromatography–mass spectrometry (LC–MS) demonstrated that the diacetylated lactonic 18:1 SL was the most abundant SL of the mixture, followed by the correspondent acidic form. The surface tension‐lowering capacity was studied in a water–air interface at temperatures ranging from 15 to 50 °C. The minimum surface tension and critical micelle concentration were determined. The emulsion properties were similar to those obtained for the commercial nonionic surfactant Triton X‐100. The efficiency of the SL natural mixture was also proven successful for the displacement of a diesel slick. These results confirmed the effectiveness of SL produced from a real waste.

The emissions of volatile organic compounds (VOC), CH4, N2O and NH3 during the solid state fermentation process of some selected wastes to obtain different enzymes have been determined at pilot scale. Orange peel+compost (OP), hair wastes+raw sludge (HW) and winterization residue+raw sludge (WR) have been processed in duplicate in 50 L reactors to provide emission factors and to identify the different VOC families present in exhaust gaseous emissions. Ammonia emission from HW fermentation (3.2±0.5 kg Mg(-1) dry matter) and VOC emission during OP processes (18±6 kg Mg(-1) dry matter) should be considered in an industrial application of these processes. Terpenes have been the most emitted VOC family during all the processes although the emission of sulphide molecules during HW SSF is notable. The most emitted compound was dimethyl disulfide in HW and WR processes, and limonene in the SSF of OP.