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J. A. Thorn and J. W. Ross. Copyright 1960 by the American Association of Cereal Chemists, Inc. Yeast cells were quantitatively recovered from dough by a process in which the dough was blended, the starch was gelatinized by heat-treatment, and the major part of the starch and protein was solubilized by digestion and fungal amylase and protease. After removal of lipids by an acid extraction with ethanol-ether, a further enzymatic digestion provided a suspension containing the yeast cells but very little extraneous material. The cells were readily counted in a Petroff-Hausser chamber, and buds were easily distinguished. The method was used to determine the amount of growth undergone by compressed and active dry yeasts in various types of commercial doughs. In sponges, both yeasts grew about 50--60% in 4 hours, but no further increase occurred in the sponge doughs. The yeasts grew about 35% in straight doughs fermented 3--3.5 hours. Most of the bud formation occurred during pan proof. No growth was found in sweet dough sponges or in flour brews fermented 3.5--4 hours. Because recovery varied during the course of dough fermentation, the nitrogen content of the isolated yeast could not be used as an indication of growth. |
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