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J. G. Ponte, Jr., R. L. Glass, and W. F. Geddes. Copyright 1960 by the American Association of Cereal Chemists, Inc. A series of comparative studies was made of active dry yeast (ADY) and compressed yeast which had been suspended, prior to use in doughs, at temperatures from 5 to 50 C. When ADY was rehydrated at 40 C. a minimum (5% of the dry weight) of material was leached from the cells. At this temperature of rehydration, baking performance was optimum and comparable to that of compressed yeast. ADY doughs required a shorter mixing time and higher levels of oxidizing improver than compressed yeast doughs. As the temperature of rehydration of ADY was lowered from 40 C. the amount of material leached from the cell increased to a maximum of 29% of the dry weight of the cells at 5 C. Nitrogenous compounds leached from ADY increased from 3.9 to 11.7 mg. nitrogen per g. yeast and glutathione from 2.2 to 9.9 mg. per g. yeast. No glutathione was found in the compressed yeast supernatants, and nitrogen appeared only in relatively small quantities at all temperatures tested. Two distinct effects resulted as the temperature of rehydration of ADY was lowered. The doughs became progressively more sticky and difficult to handle. Rheological tests showed a marked increase in extensibility and a lessened response to oxidizing agents. Identical results could be obtained by the addition of glutathione to doughs prepared using optimally rehydrated ADY. Gas production by the ADY was progressively decreased as the temperature of rehydration was lowered. This resulted in greatly decreased loaf volumes in the baked bread. This was undoubtedly due to inactivation of the cells as they progressively became more disorganized owing to the loss of cellular constituents. Compressed yeast was quite indifferent to the temperature at which it was suspended, prior to use, at all temperatures up to 40 C. At 50 C. considerably decreased loaf volumes resulted from thermal inactivation of the cells, as was also the case with ADY. |
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