Preliminary characterization and purification of novel cell-bound biosurfactant extracts from dairy residual streams

High charge contamination of dairy residual streams presents a challenge that needs to be addressed for their valorization. This work offers an alternative to the production of biosurfactants through controlled fermentation using lactic acid bacteria and costly nutritional supplements, promoting sustainability and a circular economy. Biosurfactants were extracted from microbial biomass contained in dairy waste by solid-liquid extraction with PBS, without the addition of external nutritional supplements, and then purified by dialysis. The results show that it is possible to obtain biosurfactant extracts with a lower critical micellar concentration than those produced in controlled fermentation with lactic acid bacteria (0.15 g/L) and with a consistent emulsifier activity. Moreover, the biosurfactant extracts have shown reduced contact angles on glass ranging from 45.1° ± 1.1° to 20.2° ± 1.1°, and an important oil spreading activity (34.95 ± 1.45 cm²). An incubation step of dairy waste at 37°C, without the addition of any other nutritional supplement, increased the yield of biosurfactant extract per liter of dairy waste, and we observed differences in extraction yields depending on the supplier (0.031 ± 0.003 g/L to 3.778 ± 0.130 g/L). The microbial isolates from the whey samples with higher yields were identified as Lactobacillus paracasei, Lactobacillus fermentum, and Acetobacter pasteurianus. Regarding composition, biosurfactant extracts are a mixture of lipopeptides and glycopeptides, but with lipopeptides being predominant. This is a specific characteristic of these dairy biosurfactant extracts produced from the autochthonous microbial biomass contained in whey. Both biosurfactant extracts demonstrated a zeta potential exceeding -30 mV, indicating sufficient surface charge to maintain colloidal stability and prevent aggregation with a nanoparticle size distribution of 175.4 nm or 214.8 nm.