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ABSTRACT Cereal Chem. 80(4):454-458
The effects of freezing and frozen storage of bread dough and compressed yeast on bread quality were studied. Besides, the effects of compressed yeast freezing on cell viability, gas production and release of substances by the yeast cells were examined. Freezing and frozen storage of dough made with fresh yeast had more negative effects on baking quality than the addition of frozen yeast to dough. When the compressed yeast is frozen and stored at -18[degrees]C, the CO2 production decreased, while the amount of dead cells, the total protein, and the total reducing sub-stances leached from the yeast increased as the length of yeast frozen storage increased. SDS-PAGE showed that the substances leached from frozen yeast caused an increase in the solubility of some gluten proteins. On the other hand, size-exclusion chromatography (SEC) pointed out that the relative amount of two protein fractions of low molecular weight leached from frozen yeast increased for longer yeast frozen storage periods. The yeast leachates had an adverse effect on loaf volume.
In many countries, bread (crusty type) is usually consumed fresh, and it has a very short shelf life (one to two days) even when packaged. Frozen doughs can provide fresh products daily. The main consequences of bread dough freezing and frozen storage conditions are the production of bread with lower specific loaf volume, longer proof times, and stronger alteration of textural properties (WoIt and D'Appolonia 1984; Dubois and Blockolsky 1986; Neyreneuf and Van Der Plaat 1991; Inoue and Bushuk 1992; Rasanen et al 1997; Ribotta et al 2001).
In frozen dough manufacturing, yeast survival and gas retention are major problems (Hino et al 1987). Poor gas retention during proofing can result from damage of the three-dimensional gluten protein network. Dough weakening during frozen storage and successive freeze-thaw cycles has been attributed to the release of reducing substances such as glutathione from yeast during freezing (Kline and Sugihara 1968; Hsu et al 1979). Other workers (Varriano-Marston et al 1980; WoIt and D'Appolonia 1984; Autio and Sinda 1992) have suggested that the structural changes in freeze-thawed dough are not associated with the release of reducing substances from yeast cells but with a lack of gluten cross-linking. Berglund et al (1991) showed that the formation...