SCREENING OF INDIGENOUS BIOSURFACTANT-PRODUCING BACTERIA ISOLATED FROM SOAPSTOCK

This study aimed to isolate and screen indigenous biosurfactant-producing bacteria from soapstock, a waste byproduct from the biodiesel industry. Samples were plated on PDA, TSA, and their respective variants enriched with 2% wt. glycerol. Forty-five morphologically distinct isolates were obtained and submitted to hemolytic activity screening on sheep blood agar, with 22 isolates testing positive. The isolated strains were cultivated in a minimal salt medium containing 2% (v/v) glycerol at 35 °C, 150 rpm for 5 days. Biosurfactant production was evaluated using surface tension (Du Noüy method), emulsification index (E24 with hexane), and oil displacement diameter on Petri dishes. Five strains showed promising activities, including a significant drop in surface tension (below 33 mN/m), an emulsification index above 53%, and oil displacement diameters of up to 8.8 cm. These results suggest that soapstock harbors valuable microbial strains for biosurfactant production under low-cost and sustainable conditions.