A rapid and simple assay to measure flocculation in brewer's yeast.

Akiyama-Jibiki, M., Ishibiki, T., Yamashita, H. and Eto, M.

Abstract
When a suspension of yeast cells in sodium acetate buffer solution is loaded onto a Sepharose gel column, followed by more buffer solution to which sodium chloride has been added, cells with a high surface hydrophobicity are retained in the column whereas those with a low hydrophobicity pass out of it in the eluent. The spectrophotometric determination of the yeast content of this eluent and of a second eluent collected after the retained cells have been released by adding isopropanol to the column indicates the relative numbers of highly hydrophobic and less hydrophobic cells in the sample. The "hydrophobic interaction chromatography for flocculation" (HICF) value, a measure of the size of the retained cell fraction relative to the whole sample, has been experimentally shown to be proportional to the degree of flocculence of the sample as measured by (for instance) Helm's method. When mixed samples made up from a flocculent and a nonflocculent strain are tested, the HICF value is intermediate between those of the two pure strains and varies in a linear manner according to the proportions of the two strains in the mixture (thus a mixture in equal parts has a value half way between the two pure strain values). Using this method, it has also been shown that the cell surface hydrophobicity of both flocculent and nonflocculent strains of brewers' yeast changes over the course of the fermentation process, albeit in a different manner in each case, and that old cells with a larger number of budding scars tend to be more hydrophobic than younger cells of the same strain.
Keywords : brewers' yeast chromatography flocculation measurement