tent mixing of the SSF mixture showed a 22% increment in
the fat consumption and a 31% increase in the SL yield, which
was 0.235 g per g of DM or 25. 1 g per 100 g of wet substrates
(Jiménez-Peñalver et al., 2016). From these observations, we
concluded that intermittent mixing increases the bioavailability
of substrates to the yeast; therefore, more fats are consumed
and more SLs produced.
A PROMISING PROCESS
As our studies demonstrated, WOC is a feasible substrate
for producing SLs by SSF using sugar beet molasses as the
co-substrate and Starmerella bombicola as the microorganism.
The SL yield at 10 days of fermentation was 0.179 g per g of
DM, and increased to 0.235 g per g of DM when intermittent
mixing was performed to the SSF mixture. The use of WOC
to produce high-value products such as SLs could valorize
vegetable oil refining by providing new revenue streams
for a waste product that would otherwise be composted.
Scale-up experiments using a 200-L rotating reactor are
being conducted to evaluate the economic feasibility of the
process. Moreover, oil cakes from other types of oil are being
considered as substrates for SL production.
FIG. 4. Amber colored, honey-like semi-crystalline sophorolipids
Jiménez-Peñalver, P., T. Gea, A. Sánchez, and X. Font,
Production of sophorolipids from winterization oil cake
by Solid-state fermentation: optimization, monitoring,
and effect of mixing, Biochem. Eng. J. 115: 93–100, 2016.
Krieger, N., D.C. Neto, and D.A. Mitchell, Production of
Microbial Biosurfactants by Solid-State Cultivation, In:
Biosurfactants, pp. 203–210, 2010.
Mitchell, D.A., M. Berovič, and N. Krieger, Solid-State
Fermentation Bioreactor Fundamentals: Introduction
and Overview, In: Mitchell, D.A., Berovič, M., Krieger,
N. (Eds.), Solid-State Fermentation Bioreactors:
Fundamentals of Design and Operation, Springer Berlin
Heidelberg, Berlin, Heidelberg, pp. 1–12, 2006.
Ponsá, S., T. Gea, and A. Sánchez, Different indices
to express biodegradability in organic solid wastes, J.
Environ. Qual. 39: 706–12, 2010.
Van Bogaert, I.N.A., J. Zhang, and W. Soetaert, Microbial
synthesis of sophorolipids, Process Biochem. 46: 821–
Pedro Jiménez-Peñalver is a PhD student in the Composting
Research Group (GICOM) within the Department of Chemical,
Biological and Environmental Engineering at Universitat
Autònoma de Barcelona (Spain). His work focuses on the production of sophorolipids through solid-state fermentation from both
pure substrates and agro-industrial wastes. He can be contacted
Xavier Font and Teresa Gea are professors in the Department of
Chemical, Biological and Environmental Engineering at UAB, and
researchers in the Composting Research Group (GICOM, www.
gicom.cat, firstname.lastname@example.org). The group has conducted research
on the composting and anaerobic digestion of industrial and
urban wastes since 1999. More recently, the group’s research
has shifted to increasing the valorization of wastes beyond compost and biogas by using solid state fermentation to obtain valuable products and change the paradigm from waste to feedstock
to from waste to product.
The authors thank the Spanish Ministerio de Economía y
Competitividad (Project C TM2015-69513-R) for their financial support. Pedro Jiménez has a doctoral scholarship
from the Spanish Ministerio de Economía y Competitividad