Marek Adamczak

Influence of medium composition and aeration on the synthesis of biosurfactants produced by Candida antarctica

Candida antarctica synthesised surface-active mannosylerythritol lipids at 46 g l−1 by adding 80 g soybean oil l−1 to the medium and maintaining the pO2 at 50% with an air flow rate 1 vvm. Two-stage culturing of C. antarctica avoided medium foaming but the yield of biosurfactants synthesis was 28 g l−1. The biosurfactants decreased the surface tension of water to 35 mN m−1.

Evaluation of waste products in the synthesis of surfactants by yeasts

The highest yields of biosurfactants were obtained by: (i) Pseudozyma antarctica (107.2 g L−1) cultivated in a medium containing post-refining waste; (ii) Pseudozyma aphidis (77.7 g L−1); and (iii) Starmerella bombicola (93.8 g L−1) both cultivated in a medium with soapstock; (iv)Pichia jadinii (67.3 g L−1) cultivated in a medium supplemented with waste frying oil. It was found that the biosurfactant synthesis yield increased in all strains when the cell surface hydrophobicity reached 70–80 %, enabling the microbial cells to make good contact with hydrophobic substrates. The lowest surface tension of the post-cultivation medium was from 32.0 mN m−1 to 37.8 mN m−1. However, this parameter (which was also determined by a drop collapse assay) was of limited use in monitoring biosurfactant synthesis in this study. The crude glycerol was not a good substrate for biosurfactant synthesis although, in the case of P. aphidis, 67.4 g L−1 of biosurfactants were obtained after cultivation in the medium supplemented with glycerol fraction (GF2). In a low-cost medium containing soapstock and whey permeate or molasses, about 90 g L−1 of mannosylerythritol lipids were synthesised by P. aphidis and approximately 40 g L−1 by P. antarctica.