Yeast for Frozen Dough

yasmaya blok-1The use of frozen dough’s is gradually increasing in most countries because it offers great convenience, automation and economy of scale. On the other hand, significant reduction of the leavening capacity during freeze storage is a serious problem. Minimizing this loss requires dedicated equipment for cold and rapid mixing of the dough which is not available to all bakers. Furthermore, these optimized production conditions still may not completely overcome the drop in leavening activity. Conditions for production of baker’s yeast have been optimized in the past decades and nowadays allow yeast with a very high stress resistance to be produced. However, the preparation of frozen dough’s presents an unusual challenge. A short pre-fermentation period before freezing of the dough is required to obtain an appropriate texture in the bread. Consequently, fermentation-induced loss of stress resistance is a central problem to the production of frozen dough’s. Neither the addition of more yeast or of protective additives nor the optimization of dough production conditions has resulted in a satisfying solution for the loss of rising capacity in frozen dough’s. Yeast strains with improved freeze tolerance have been isolated from natural sources, selected from culture collections, or obtained by mutagenesis, hybridization, or protoplast fusion of natural and commercial strains. Upon characterization of those strains, interest has focused on trehalose as an important physiological factor of yeast cryoresistance. This particular disaccharide, which can accumulate up to 20% of the cellular dry weight, was considered an energetic reserve as well as a stress metabolite. It was shown that trehalose could be used as a powerful cryoprotectant for yeast when frozen in water. Furthermore, several scientists reported that it imparts a higher cryoresistance to baker’s yeast in dough. The strains selected during screenings of yeasts suitable for frozen dough showed higher trehalose contents than less cryoresistant strains. Trehalose accumulated during strongly aerobic culture may have had a cryoprotective effect on Saccharomyces cerevisiae. High trehalose content was beneficial for good freeze-thaw stability after extended storage. These authors also pointed out; however, that high trehalose content was not always related to a higher cryoresistance. It was demonstrated that the freezing tolerance of yeast strains was, to some extent, associated with the basal amount of trehalose maintained after a prefermentation period.