Response Surface Methodology for Optimizing the Production of Biosurfactant by Candida tropicalis on Industrial Waste Substrates.

Darne G Almeida,Leonie A Sarubbo,Raquel D Rufino,Valdemir A Santos,Rita De Cássia F Soares Da Silva,Juliana M Luna

doi:10.3389/fmicb.2017.00157

Abstract

Biosurfactant production optimization by Candida tropicalis UCP0996 was studied combining central composite rotational design (CCRD) and response surface methodology (RSM). The factors selected for optimization of the culture conditions were sugarcane molasses, corn steep liquor, waste frying oil concentrations and inoculum size. The response variables were surface tension and biosurfactant yield. All factors studied were important within the ranges investigated. The two empirical forecast models developed through RSM were found to be adequate for describing biosurfactant production with regard to surface tension (R2 = 0.99833) and biosurfactant yield (R2 = 0.98927) and a very strong, negative, linear correlation was found between the two response variables studied (r = −0.95). The maximum reduction in surface tension and the highest biosurfactant yield were 29.98 mNm−1 and 4.19 gL−1, respectively, which were simultaneously obtained under the optimum conditions of 2.5% waste frying oil, 2.5%, corn steep liquor, 2.5% molasses, and 2% inoculum size. To validate the efficiency of the statistically optimized variables, biosurfactant production was also carried out in 2 and 50 L bioreactors, with yields of 5.87 and 7.36 gL−1, respectively. Finally, the biosurfactant was applied in motor oil dispersion, reaching up to 75% dispersion. Results demonstrated that the CCRD was suitable for identifying the optimum production conditions and that the new biosurfactant is a promising dispersant for application in the oil industry.

Highlights

Surfactants are amphipathic molecules that reduce the surface and interfacial tensions of liquids (Santos et al, 2013; Silva et al, 2014a)
The majority of biosurfactants have been reported in bacteria, the pathogenic nature of some producers restricts the wide application of these compounds (Toribio et al, 2010; Sharma et al, 2016)
The best condition for biosurfactant production was found in Run 1 for both response variables, as the lowest surface tension coincided with the highest biosurfactant yield

Summary

Introduction

Surfactants are amphipathic molecules that reduce the surface and interfacial tensions of liquids (Santos et al, 2013; Silva et al, 2014a) Such compounds have a predilection for interfaces of dissimilar polarities (liquid–air or liquid–liquid) and are soluble in both organic (non-polar) and aqueous (polar) solvents (Luna et al, 2013). Due to these properties, surfactants have a wide variety of applications in medicine, household products, agriculture, food products, cosmetics, pharmaceuticals, and the petroleum industry (Rufino et al, 2014). Some species of Candida, such as Candida bombicola (Roelants et al, 2013; Luna et al, 2016), Candida glabrata (Luna et al, 2009; Gusmão et al, 2010), Candida lipolytica (Santos et al, 2013; Rufino et al, 2014), Candida sphaerica (Sobrinho et al, 2013a; Luna et al, 2015), Candida utilis (Campos et al, 2013), Candida guilliermondii (Sitohy et al, 2010), Candida antarctica (Kim et al, 2002; Hua et al, 2003), and Candida tropicalis (Batista et al, 2010; Priji et al, 2013) are known to produce biosurfactant

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