Production and characterization of sophorolipids from stearic acid by solid-state fermentation, a cleaner alternative to chemical surfactants

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 (08:0), 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 solid-state 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. (C) 2017 Elsevier Ltd. All rights reserved.