Medium-size droplets of methyl ricinoleate are reduced by cell-surface activity in the gamma-decalactone production by Yarrowia lipolytica.

International audienceSize of methyl ricinoleate droplets during biotransformation into gamma-decalactone by Yarrowia lipolytica was measured in both homogenized and non-homogenized media. In non-homogenized but shaken medium, droplets had an average volume surface diameter d32 of 2.5 microm whereas it was 0.7 microm in homogenized and shaken medium. But as soon as yeast cells were inoculated, both diameters became similar at about 0.7 microm and did not vary significantly until the end of the culture. The growth of Y. lipolytica in both media was very similar except for the lag phase which was lowered in homogenized medium conditions

Medium-size droplets of methyl ricinoleate are reduced by cell-surface activity in the γ-decalactone production by Yarrowia lipolytica

Size of methyl ricinoleate droplets during biotransformation into γ-decalactone by Yarrowia lipolytica was measured in both homogenized and non-homogenized media. In non-homogenized but shaken medium, droplets had an average volume surface diameter d 32 of 2.5 μm whereas it was 0.7 μm in homogenized and shaken medium. But as soon as yeast cells were inoculated, both diameters became similar at about 0.7 μm and did not vary significantly until the end of the culture. The growth of Y. lipolytica in both media was very similar except for the lag phase which was lowered in homogenized medium conditions

Thermally Induced Gelling of Oil-in-Water Emulsions Comprising Partially Crystallized Droplets: The Impact of Interfacial Crystals

We produced triglyceride-in-water emulsions comprising partially crystallized droplets, stabilized by a mixture of protein and low molecular weight surfactant. The emulsions were emulsified in the melted state of the oil phase and stored at low temperature (4 °C) right after fabrication to induce oil crystallization. The systems were then warmed to room temperature for a short period of time and cooled again to 4 °C. Owing to this treatment referred to as temperature cycling or “tempering”, the initially fluid emulsions turned into hard gels.Wefollowed the bulk rheological properties of the materials during and after tempering. The storage modulus, G′, exhibited a dramatic increase when tempering was applied. We showed that the systems evolved following two distinct regimes that depend on the average droplet size and on the surfactant-to-protein molar ratio. Gelling may involve partial coalescence of the droplets, i.e., film rupturing with no further shape relaxation because of the solid nature of the droplets. Alternatively, gelling may occur without film rupturing, and is reminiscent of a jamming transition induced by surface roughness. We discussed the origin of these two mechanisms in terms of the properties (size and protuberance) of the interfacial oil crystals