Figure 1.

Yield of sophorolipids from horse oil and hydrolysed horse oil, and the effects of pH and glucose concentration on yeast growth and sophorolipid yield. To establish optimal conditions, horse oil was diluted with water to different concentrations in flask cultures and treated with 0.3% lipase at 35°C with stirring for 1 h, and sophorolipids were measured using the solvent extraction method (A). Data are presented as the mean ± SD from three separate experiments respectively. *p < 0.05 or ***p < 0.001 vs. corresponding horse oil group. Dynamic profiles of yeast growth status, evaluated by dry cell weight (DCW), sophorolipid concentrations, pH values and glucose concentrations in the 5 L jar fermenter were measured at different time points during routine fermentation (B) and fed‐batch fermentation (C) in which pH was maintained above 4 by frequent addition of glucose after 50 h of fermentation. Data are presented as the mean ± SD from three separate experiments respectively. *p < 0.05 vs. controls (time = 0); **p < 0.01 vs. controls (time = 0); ***p < 0.001 vs. controls (time = 0).