Potential brewer’s spent grain as a carbon source alternative for biosurfactant production by Rhodotorula mucilaginosa (LBP4)

Abstract

This study promoted the valorization of brewer’s spent grain (BSG) by using it as an alternative and low-cost carbon source in the production of biosurfactant by Rhodothorula mucilaginosa (LPB4) in an optimized process. The raw BSG was characterized: moisture content (80.0%), insoluble and soluble lignin (29.25%), proteins (6.43%), ash (4.22%), cellulose (47.37%) and pH (6.06), then to verify the increase of reducing sugars, BSG was tested by microwave-assisted alkali and diluted acid pretreatments and then the BSG with and without pretreatment were subjected to enzymatic hydrolysis. The microwave-assisted alkali, followed by enzymatic hydrolysis, achieved 181 mg of sugar.g-1 of BSG and was the most effective. The hydrolysate was used as a carbon source for the biosurfactant production assays and optimized under the following conditions: 30ºC, 120 rpm, 2.5 g.L- 1 of sugar, and pH 4. The biosurfactant was able to emulsify (%E24) different hydrophobic substrates, which were as follows: soybean oil (64.4%), motor oil (62.2%), kerosene (67.4%) and diesel oil (56.81%). Also, it showed stability under extreme temperatures, pH, and salinity. A critical micelle concentration (CMC) of 14.8 mg.mL- 1 was achieved with a decrease in surface tension (ST) from 71.26 mN.m-1 to 30.56 mN.m- 1. The extracted biosurfactant showed an anionic nature and structural similarities to a glycolipid. The present findings revealed that pretreated BSG may be used as a substrate in biosurfactant production using the yeast R. mucilaginosa. This is the first study regarding using LBP4 to optimize the production of biosurfactant using alkali enzymatic BSG hydrolysate.