From Winery Waste to Biosurfactants: White Grape Pomace Fractionation, Characterization and Bioconversion Towards Sophorolipids

The wine industry generates significant quantities of agro-industrial waste, with grape pomace representing its main fraction. White grape pomace (WGP), rich in fermentable sugars and lipids, can serve as a substrate for biosurfactant production. In this study, the sugar fraction of WGP was used as substrate to produce sophorolipids (SL), a class of microbial biosurfactants, by the yeast Starmerella bombicola. To examine efficient SL production, both a sugar source and lipid source were examined. Three lipid sources were tested: grape seed oil (GSO) extracted from WGP, spent frying oil (SFO), and rapeseed oil (RO), the later serving as a commercial reference. WGP-aqueous extraction yielded a sugar-rich fraction (WSE, 67% w/w) comprising ca. 97% carbohydrates, of which 60% were free sugars, mainly glucose and fructose. GSO accounted for 11% of the seeds’ weight and was predominantly composed of esterified linoleic (71%) and oleic (18%) acids. Bola-type SL were produced under optimized shake-flask conditions at 30 °C and 200 rpm in all WSE conditions, with SFO yielding the highest SL concentration (6.03 g/L), attributed to its oleic acid richness, and GSO yielding 3.75 g/L. This work demonstrates the potential of WGP-derived biomolecules as low-cost alternatives to first-generation substrates (commercial glucose and RO) in SL production by S. bombicola, contributing to the development of sustainable biosurfactants that can serve as a green alternative to petroleum-based surfactants, while reducing the environmental footprint of the wine industry.