Utilization of distillers dried grains with solubles as a cheaper substrate for sophorolipid production by Rhodotorula babjevae YS3

Abstract

Sophorolipids (SLs) are a class of glycolipid biosurfactant with excellent surface-active properties, large yields, and appreciable antimicrobial properties. However, their commercial applications remain limited due to high production costs, primarily due to high-priced substrates. Therefore, the present work aims to utilize corn and rice-based distillers dried grains with solubles (DDGS), a by-product of the ethanol production industry, as low-cost substrates for cheaper SL production. Maximum SL production was achieved after 72 h of fermentation at 17.81 gL−1 using rice DDGS (SL-R) and 19.27 gL−1 for corn DDGS (SL-C). SL-C and SL-R reduced surface tension (ST) of water to 34 mN m−1 (CMC 120 mg L−1) and 37 mN m−1 (CMC 110 mg L−1), respectively. SL-R and SL-C both exhibited stable surface activity over a wide range of – pH 2.0–12.0, salinity 2.0–12.0% (w/v), and heating time 0–120 min at 120 °C). SL-R exhibited the highest emulsifying activity (E24 100%) against crude oil. Structural characterization using FT-IR, LC-MS, and GC-MS revealed the SLs to be a mixture of acidic and lactonic forms. The SLs also exhibited potential for application as an antimicrobial agent against a wide range of bacterial and fungal pathogens, confirming its potential for biomedical applications. The results highlight the application of DDGS as a substrate for SL production, which is cheap and readily available, thereby lowering production costs (about $1.5 kg−1 of SL). In comparison to previous studies, we claim that this production process contributed to an almost 50% reduction in production costs.