Encapsulation of flavours into Yarrowia lipolytica active yeast cells. Fluorescence study of the lipid droplets morphology and steryl/sterol balance during the shock

Yeast are a powerful material for the encapsulation of compounds. Usually, yeast used as capsules are inactivated by the encapsulation treatment, which is stressful to cells. However, if kept active, cells can bring their own activity in addition to the encapsulated compound. We have observed previously that lipid-grown Yarrowia lipolytica were more resistant to encapsulation. The objective of the present study was to identify physiological markers involved in this resistance. Cells were cultured in the presence of glucose or methyl-oleate as the sole carbon source and submitted to a γ-dodecalactone stress. This paper focuses on the role of intracellular lipid droplets (LDs) and of the ergosteryl content to protect cells during the lactone treatment. Lipid-grown cells were more resistant to lactone and the presence of LDs before the shock increased significantly the resistance. The ergosteryl esters from the LD pool were hydrolysed to release ergosterol able to strenghten the plasma membrane during the shock. For cells devoid of LDs, membrane ergosterols were esterified concomitantly with LDs growth, resulting in a membrane weakening. By using pox3-mutant strains, which possesse numerous and small-sized LDs, we observed the original behaviour: these mutants showed no increased resistance and their LDs exploded in the cytoplasma during the shock. These results point out the role of LDs in cell resistance to amphiphilic stresses as a storage compartment as well as in ergosterol homeostasis.