Spent coffee grounds as feedstock for the production of biosurfactants and the improved recovery of melanoidins.

Spent coffee grounds (SCG) are wastes generated in high amounts worldwide. Their composition makes them a promising feedstock for biotechnological processes. Here we show that the production of the biosurfactant surfactin by submerged culture of a Bacillus subtilis strain growing on SCG is possible, reaching concentrations up to 8.8 mg/L when using SCG at 8.3 g/L in the medium. In addition, we report a synergy between the production of surfactin and the recovery of melanoidins, an added-value compound already present in SCG. More specifically, the concentration of melanoidins in the culture medium increased between 2.1 and 2.5 times thanks to the presence of the B. subtilis in the culture. Furthermore, we have observed a strong interaction between surfactin and melanoidin aggregates through dynamic light scattering measurements, and that both of them can be co-purified with an acid precipitation. We have also characterized the interfacial and antioxidant properties of the cell-free supernatant and surfactin extract, as well as the distribution of the congeners of the biosurfactant. Altogether, this work describes a promising approach to obtain biosurfactants and antioxidant molecules in a single operation, which can be used to design several new formulations of interest for bioremediation, amendment of soils, food and cosmetics.

Biosurfactant production by Trametes versicolor grown on two-phase olive mill waste in solid-state fermentation.

Biosurfactants are amphiphilic compounds of microbial origin which exhibit better properties than their chemically derived counterparts. They are usually produced in submerged fermentation by different types of bacteria. However, biosurfactant production by fungi, particularly of the white-rot type, has been scarcely studied. In this work, and for the first time, we report the production of biosurfactants by the white-rot fungus Trametes versicolor, which was grown on two-phase olive mill waste (TPOMW) in a solid-state fermentation system. The effect of the composition of the culture medium on biosurfactant production was also studied. The highest biosurfactant production (373.6 ± 19.4 mg in 100 g of culture medium) was achieved with a medium containing 35% (w/w) of TPOMW, the highest concentration used, 10% of wheat bran and 55% of olive stones. Interestingly, no inhibition of biosurfactant production by TPOMW was detected within the concentration range used (5-35% w/w). The biosurfactant produced by T. versicolor was able to reduce the surface tension of an aqueous extract of the culture medium up to 34.5 ± 0.3 mN m-1. A preliminary study of the chemical structure of the biosurfactant indicated that it contains both lipid and protein fractions. The simultaneous production of lignin-degrading enzymes was also assessed.

Aquatic toxicity and biodegradability of a surfactant produced by Bacillus subtilis ICA56.

In this work, the environmental compatibility of a biosurfactant produced by a Bacillus subtilis strain isolated from the soil of a Brazilian mangrove was investigated. The biosurfactant, identified as surfactin, is able to reduce surface tension (ST) to 31.5 ± 0.1 mN m-1 and exhibits a lowcritical micelle concentration (CMC) value (0.015 ± 0.003 g L-1). The highest crude biosurfactant concentration (224.3 ± 1.9 mg L-1) was reached at 72 h of fermentation. Acute toxicity tests, carried out with Daphnia magna, Vibrio fischeri and Selenastrum capricornutum indicated that the toxicity of the biosurfactant is lower than that of its chemically derived counterparts. The results of the biodegradability tests demonstrated that the crude surfactin extract was degraded by both Pseudomonas putida and a mixed population from a sewage-treatment plant, in both cases the biodegradation efficiency being dependent on the initial concentration of the biosurfactant. Finally, as the biodegradation percentages obtained fall within the acceptance limits established by the Organization for Economic Co-operation and Development (Guidelines for Testing of Chemicals, OECD 301E), crude surfactin can be classified as a "readily" biodegradable compound.

Hydrolysis of olive mill waste to enhance rhamnolipids and surfactin production.

The aim of this work was to demonstrate the effectiveness of hydrolysis pretreatment of olive mill (OMW) waste before use as a carbon source in biosurfactant production by fermentation. Three hydrolysis methods were assessed: enzymatic hydrolysis, acid pretreatment plus enzymatic hydrolysis, and acid hydrolysis. Fermentation was carried out using two bacterial species: Pseudomonas aeruginosa and Bacillus subtilis. Our results showed that the enzymatic hydrolysis was the best pretreatment, yielding up to 29.5 and 13.7mg/L of rhamnolipids and surfactins respectively. Glucose did not show significant differences in comparison to enzymatically hydrolysed OMW. At the best conditions found rhamnolipids and surfactins reached concentrations of 299 and 26.5mg/L; values considerably higher than those obtained with non-hydrolysed OMW. In addition, enzymatic pretreatment seemed to partially reduce the inhibitory effects of OMW on surfactin production. Therefore, enzymatic hydrolysis proved to effectively increase the productivity of these biosurfactants using OMW as the sole carbon source.

Rhamnolipid and surfactin production from olive oil mill waste as sole carbon source.

Olive mill waste (OMW) creates a major environmental problem due to the difficulty of further waste processing. In this work we present an approach to give OMW added value by using it for the production of biosurfactants. Two bacterial species, Pseudomonas aeruginosa and Bacillus subtilis, were grown with OMW as the sole carbon source. Glycerol and waste frying oil were used as comparative carbon sources. B. subtilis produced surfactin (a lipopeptide) at a maximum concentration of 3.12 mg/L with 2% w/v of OMW in the medium, dropping to 0.57 mg/L with 10% w/v of OMW. In contrast, P. aeruginosa produced 8.78 mg/L of rhamnolipid with 2% w/v OMW increasing to 191.46 mg/L with 10% w/v OMW. The use of solvent-extracted OMW reduced the biosurfactant production by 70.8% and 88.3% for B. subtilis and P. aeruginosa respectively. These results confirm that OMW is a potential substrate for biosurfactant production.

Rheology and dynamics of micellar cubic phases and related emulsions.

The rheological behavior of micellar cubic phases in C12EO25 systems and related emulsions has been investigated. In the aqueous C12EO25 binary system, the transition from the cubic phase to the micellar solution is associated with a sudden drop in viscosity and with a small enthalpy of transition. The elastic modulus and viscosity of the cubic phases show a maximum with concentration but remain very high within the range of existence of the cubic phase. Several relaxation processes seem to be present in binary cubic phases, and some of them occur in a time scale that can be followed by both rheology and dynamic light scattering measurements. Upon addition of a small amount of oil (decane), the rheological behavior changes remarkably. As the oil fraction increases, the relaxation times also increase and, finally, highly concentrated, gel-like emulsions are obtained. Contrary to conventional concentrated emulsions, the viscosity of cubic-phase-based emulsions is decreased by increasing the fraction of the dispersed phase. The non-Maxwellian rheological behavior at low oil fractions is described according to the model of slipping crystalline planes, modified by using a distribution of bulk relaxation times, and good fitting to the experimental data is obtained.