Effect of nutrient supplementation on Yarrowia lipolytica growth and emulsifying activity in cassava peel medium

Cassava (Manihot esculenta Crantz) peel is a potential low-cost substrate for microbial cultivation, but nutrient availability may restrict its utilization. This study evaluated the effect of yeast extract and ammonium sulfate supplementation on Yarrowia lipolytica cultivation and emulsifying activity in cassava peel medium. Unsupplemented and supplemented media, both containing 2.5 g/L cassava peel, were compared with YPD (g/L: yeast extract, 10; peptone, 20; glucose, 20), a yeast extract ammonium sulfate control, and a reference medium for biosurfactant production. Supplementation comprised yeast extract at 0.5 g/L and ammonium sulfate at 10 g/L. The reference medium contained the same supplements, glucose at 4% and glycerol at 2%. Y. lipolytica was precultured in YPD medium for 72 h. Cultivation was performed in 250 mL flasks containing 100 mL of medium, with an initial biomass concentration of approximately 1 g/L. Cultures were incubated in an orbital shaker at 28–29 °C and 250 rpm for 96 h, with sampling at 0, 24, 48, 72 and 96 h. Cell concentration was estimated by spectrophotometric measurement of optical density at 570 nm using a biomass calibration. Culture pH was monitored, and emulsification indices were calculated as the percentage ratio between emulsified layer height and total mixture height (EI₂₄). Means and standard deviations were calculated where duplicate observations were available. No emulsification was recorded initially. Unsupplemented cassava peel medium reached an emulsification index of 51.11% at 24 h, decreasing to 38.46% at 96 h. Supplemented medium reached 47.20% at both 48 and 96 h, with a final standard deviation of 3.96 percentage points. Its final mean was 8.74 percentage points higher than that of the unsupplemented medium and numerically identical to the reference medium. The yeast extract–ammonium sulfate control showed no emulsification throughout cultivation. Cell concentration increased from 0.86 to 1.93 g/L in unsupplemented cassava peel medium and from 0.92 to 13.34 g/L in YPD, whose final emulsification index was 45.24%. Thus, greater biomass accumulation did not necessarily correspond to greater emulsifying activity. Supplementation was associated with a higher final emulsification index, whereas the unsupplemented medium exhibited an earlier and higher maximum. These findings support cassava peel as a substrate for obtaining emulsifying activity and indicate that supplementation affects its temporal profile. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. The authors also acknowledge the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for financial support.