AbstractThe toxicity of an Alamine 336/oleyl‐alcohol extraction system on Lactobacillus delbrueckii was investigated. It was shown that the solvent affected the cells through the water‐soluble portion and the immiscible portion of the solvent. While immobilization significantly protected the cells from the immiscible solvent phase, the water‐soluble part of the solvent still caused toxicity to the microorganisms due to diffusion of the solvent into the matrix. Adding soybean oil to the κ‐carrageenan matrix could trap the diffusing solvent molecules, and therefore reduce the toxic effect from the water soluble portion of the solvent. The protective ability of soybean oil was quantified through mathematical modeling and experimentation.