Production of biosurfactant by Achromobacter sp. GY30 from waste glycerol and potential application for vegetable oil extraction

Abstract

Vegetable oil is commonly extracted from oilseeds by solvent extraction with hexane. However, hexane is volatile and toxic to human and environment. To reduce the use of hexane, alternative methods of oil extraction have been developed such as aqueous extraction process (AEP). Nevertheless, AEP by using water alone has low oil extraction efficiency. Biosurfactant can be used to improve the oil extraction yield in AEP. Although the use of biosurfactants has been increasing over the year, their large scale production and application are limited with high production cost and low productivity. In this study, an effective biosurfant-producing bacterium was isolated and selected for investigated their optimum medium composition and examined for their potential application in vegetable oil extraction. Achromobacter sp. GY30 which produced low surface and interfacial tension of medium, high E₂₄ (%) with vegetable oil, and high oil detachment (%), was selected as an effective biosurfactant-producing bacterium. Strain GY30 was then determined for its optimum culture medium composition for biosurfactant production. The parameters affected biosurfactant production; waste glycerol concentration, nitrogen source and concentration, C/N ratio, and precursor supplementation, were evaluated by using classical method (study one factor at a time) and experimental design. From using the classical method, increasing biosurfactant yield of 2 fold was observed when using 5% (w/v) waste glycerol, 0.4% (w/v) NaNO₃, and supplemented with 0.1% (v/v) palm oil. The best culture medium composition of 7% (w/v) waste glycerol, 0.4% (w/v) NaNO₃, and supplemented with 0.01% (v/v) palm oil, correlated to C/N ratio of 42, was obtained when using experimental design. It produced high biosurfactant yield of 0.79 (g/l). Moreover, it could enhance productivity 20% from the previous experiment. Then, the potential application of biosurfactant from strain GY30 in vegetable oil extraction was studied. The highest oil detachment of 60% was obtained when using cell-free broth. In addition, it was found that isolated biosurfactant solution could extract palm kernel oil in free oil form which is favorable in the oil extraction process. For free fatty acid content, it was found that extracted oil from this method was comparable to those of the hexane method and much better than those of mechanical pressing. Thus, the use of isolated biosurfactant in aqueous-based method for palm kernel oil extraction was of the interest alternative method for reducing the use of hexane.