Leavening Ability In Dough Research Articles

Effect of overexpression of SNF1 on the transcriptional and metabolic landscape of baker\u2019s yeast under freezing stress

BackgroundFreezing stress is the key factor that affecting the cell activity and fermentation performance of baker’s yeast in frozen dough production. Generally, cells protect themselves from injury and maintain metabolism by regulating gene expression and modulating metabolic patterns in stresses. The Snf1 protein kinase is an important regulator of yeast in response to stresses. In this study, we aim to study the role of the catalytic subunit of Snf1 protein kinase in the cell tolerance and dough leavening ability of baker’s yeast during freezing. Furthermore, the effects of SNF1 overexpression on the global gene expression and metabolite profile of baker’s yeast before and after freezing were analysed using RNA-sequencing and untargeted UPLC − QTOF-MS/MS, respectively.ResultsThe results suggest that overexpression of SNF1 was effective in enhancing the cell tolerance and fermentation capacity of baker’s yeast in freezing, which may be related to the upregulated proteasome, altered metabolism of carbon sources and protectant molecules, and changed cell membrane components. SNF1 overexpression altered the level of leucin, proline, serine, isoleucine, arginine, homocitrulline, glycerol, palmitic acid, lysophosphatidylcholine (LysoPC), and lysophosphatidylethanolamine (LysoPE) before freezing, conferring cells resistance in freezing. After freezing, relative high level of proline, lysine, and glycerol maintained by SNF1 overexpression with increased content of LysoPC and LysoPE.ConclusionsThis study will increase the knowledge of the cellular response of baker’s yeast cells to freezing and provide new opportunities for the breeding of low-temperature resistant strains.

Improving freeze-tolerance of baker's yeast through seamless gene deletion of NTH1 and PUT1.

Baker's yeast strains with freeze-tolerance are highly desirable to maintain high leavening ability after freezing. Enhanced intracellular concentration of trehalose and proline in yeast is linked with freeze-tolerance. In this study, we constructed baker's yeast with enhanced freeze-tolerance by simultaneous deletion of the neutral trehalase-encoded gene NTH1 and the proline oxidase-encoded gene PUT1. We first used the two-step integration-based seamless gene deletion method to separately delete NTH1 and PUT1 in haploid yeast. Subsequently, through two rounds of hybridization and sporulation-based allelic exchange and colony PCR-mediated tetrad analysis, we obtained strains with restored URA3 and deletion of NTH1 and/or PUT1. The resulting strain showed higher cell survival and dough-leavening ability after freezing compared to the wild-type strain due to enhanced accumulation of trehalose and/or proline. Moreover, mutant with simultaneous deletion of NTH1 and PUT1 exhibits the highest relative dough-leavening ability after freezing compared to mutants with single-gene deletion perhaps due to elevated levels of both trehalose and proline. These results verified that it is applicable to construct frozen dough baker's yeast using the method proposed in this paper.

産学官連携による製パン用「とかち野酵母」の開発

Eight yeast strains were isolated from samples collected in Hokkaido after enrichment culture with a high concentration of sucrose. Among them, strain AK 46, which was derived from dough containing fermented cherry fruits was identified as Saccharomyces cerevisiae. The nucleotide sequence of the rDNA spacer region from this strain was identical to those from yeasts used for the production of whisky, wine, and bread. Strain S. cerevisiae AK 46 carried only only SUC2, which is one of multiple genes that encodes invertase, in contrast to the other baking strains, and its sequences were diverged from those of the corresponding gene found in the other strains. In a comparison of six baking strains, strain AK 46 showed lower leavening ability in dough with and without the addition of 5% sucrose by weight of flour but showed high leavening ability in sweet dough containing 30% sucrose. The activities of enzymes α-glucosidase and invertase, which are related to dough fermentation, were lower than those in the other strains. A baking test showed that strain AK 46 was suitable for breadmaking by various methods. Cells of strain AK 46 were propagated industrially and used for the commercial production of dry yeast called “Tokachino”, which is named for the region from which it was isolated.

A straightforward logistic method for feeding a fed-batch baker's yeast culture

The aim of this work was to find a straightforward, low-cost method for nutrient medium delivery during fed-batch cultivation of baker's yeast; a method that provides a high specific growth rate, a high biomass yield, and a high dough-leavening ability. The time profile for the inflow of the nutrient medium, g( t), is a logistic model which takes the form of g( t) = a/(1 + be − ct ), with a, b and c standing for its parameters. The initial values of a, b and c were calculated considering the results of a baker's yeast process where dissolved oxygen tension was used as a control parameter of medium inflow. A method was developed for modifying the parameters of the initial model so as to obtain a formula that would cause the inflow of the nutrient medium to maximize the criterion K( K = Yμ), where Y stands for yeast biomass yield and μ denotes specific growth rate. The parameters of the modified model depended on initial biomass concentration. The relation was described by a logarithmic function and incorporated into the control algorithm. This algorithm produced a biomass yield exceeding 0.55 g g −1 and a high dough-leavening ability. The method proposed is recommendable for small and medium-sized firms producing baker's yeast.

Baking Properties of Saccharomyces cerevisiae Strains Derived from Brem, a Traditional Rice Wine from Bali

Twenty-two strains of Saccharomyces cerevisiae isolated from tape-mash for the production of brem, a traditional rice wine from Bali, Indonesia, were divided into three groups (I, II, and III) based on the se- quences of the rDNA spacer region and SUC2 gene. DNA analyses suggested that the seventeen strains in groups II and III were taxonomically closer to baking strains than the five strains in group I. These differ - ences were reflected in their leavening ability in dough with and without addition of 5% sucrose, and their α-glucosidase activity, although most of the strains did not leaven dough with addition of 30% sucrose. Strain S-10 in group II showed a high rate of CO2 production from sponge dough without addition of sugar and consumed fermentable sugar within 2.5 h. When baking tests were conducted, strain S-10 and commercial baking strain HP 216 yielded comparable products by the straight-dough and sponge-dough methods.

Characterization of an Alternative Baking Strain of Saccharomyces cerevisiae Isolated from Fermented Cherry Fruits by the Analysis of SUC2 Gene

The yeast strain AK 46 was isolated from dough containing fermented cherry fruits and identified as Saccharomyces cerevisiae. The nucleotide sequence of the rDNA spacer region from this strain coincided with those from the yeasts used for the production of whisky, wine, and bread. In a comparison with six baking strains, strain AK 46 possessed less leavening ability in dough with and without addition of 5% sucrose (based on the weight of flour) but a high ability in sweet dough containing 30% sucrose. The activities of the two enzymes α-glucosidase and invertase, which are related to dough fermentation, were lower than those in the other strains. A baking test showed that strain AK 46 was applicable for breadmaking using the straight dough and sponge dough methods. Strain AK 46 carried only SUC2, which is one of multiple genes encoding invertase, in contrast to the other baking strains, and its sequences diverged from those of the corresponding gene from a representative laboratory strain. Southern hybridization of genomic DNA, using the SUC2 gene as the probe, readily discriminated strain AK 46 and other strains. These observations indicate that strain AK 46 is a wild strain possessing breadmaking properties.

A novel feeding method in commercial Baker’s yeast production

The aim of this investigation was to determine a better leavening ability and shelf life for the same biomass yield of final product. A commercial fed-batch bioreactor equipped with circulation loop was used to study the effect of carbon source, molasses, profile on dough-leavening ability, shelf life and biomass yield of Baker's yeast, Saccharomyces cerevisiae. A set of 32 commercial batches were performed to investigate the effect of sugar concentration and compare with 32 control experiments. Higher local sugar concentration in circulation loop resulted in a better leavening ability and shelf life for the same biomass yield of the final product. In addition, this method improved nitrogen assimilation which resulted in higher protein content. Increase in leavening ability and protein content could be a result of the higher levels of glycolytic enzymes. It was observed that this change resulted in considerable improvement in leavening ability and shelf life at a commercial scale. It must be emphasized that to improve product quality, it is not necessary to pursue classical mutagenesis and selection strategies. A high-quality product can be achieved only by optimizing the feeding profile and strategy.

Improvement of tolerance to freeze–thaw stress of baker’s yeast by cultivation with soy peptides

The tolerance to freeze-thaw stress of yeast cells is critical for frozen-dough technology in the baking industry. In this study, we examined the effects of soy peptides on the freeze-thaw stress tolerance of yeast cells. We found that the cells cultured with soy peptides acquired improved tolerance to freeze-thaw stress and retained high leavening ability in dough after frozen storage for 7 days. The final quality of bread regarding its volume and texture was also improved by using yeast cells cultured with soy peptides. These findings promote the utilization of soy peptides as ingredients of culture media to improve the quality of baker's yeast.

Deficiency in the glycerol channel Fps1p confers increased freeze tolerance to yeast cells: application of the fps1delta mutant to frozen dough technology.

Intracellular glycerol content affects the freeze-thaw stress tolerance of Saccharomyces cerevisiae. We have recently reported that intracellular-glycerol-enriched cells cultured in glycerol medium acquire tolerance to freeze stress and retain high leavening ability even in dough after frozen storage [Izawa et al. (2004) Appl Microbiol Biotechnol http://dx.doi.org/10.1007/s00253-004-1624-4]. A deletion mutant of the FPS1 gene, which encodes a glycerol channel, accumulates glycerol inside the cell without an exogenous supply of glycerol into the medium. We found that the fps1delta cells acquired tolerance to freeze stress and retained high leavening ability in dough after frozen storage for 7 days. These results suggest that the fps1delta mutant is a useful strain for developing better frozen-dough with a commercial advantage.

Intracellular glycerol influences resistance to freeze stress in Saccharomyces cerevisiae: analysis of a quadruple mutant in glycerol dehydrogenase genes and glycerol-enriched cells.

Glycerol is well known as a cryoprotectant similar to trehalose. However, there is little information about the effects of intracellular glycerol on the freeze-thaw stress tolerance of yeast. Through analysis of a quadruple-knockout mutant of glycerol dehydrogenase genes (ara1 Delta gcy1 Delta gre3 Delta ypr1 Delta) in Saccharomyces cerevisiae, we revealed that the decrease in glycerol dehydrogenase activity led to increased levels of intracellular glycerol. We also found that this mutant showed higher tolerance to freeze stress than wild type strain W303-1A. Furthermore, we demonstrated that intracellular-glycerol-enriched cells cultured in glycerol medium acquire tolerance to freeze stress and retain high leavening ability in dough even after frozen storage for 7 days. These results suggest the possibility of using intracellular-glycerol-enriched cells to develop better frozen dough.

Leavening ability of baker’s yeast exposed to hyperosmotic media

To develop a simple and rapid method for enhancing the leavening ability of baker’s yeast, we examined the fermentation ability of baker’s yeast exposed to hyperosmotic media. When baker’s yeast cells were incubated at 25°C for 1 h in a hyperosmotic medium containing 0.5% yeast extract, 0.5% peptone and 20% sucrose, the cells showed a higher fermentation ability in the subsequent fermentation test than those untreated. The increased ratios were from 40 to 60% depending on the strains used. Glucose and fructose showed a similar effect to that of sucrose, but sorbitol was less effective. A high correlation between the intracellular glycerol content and fermentation ability after the osmotic treatment suggested that glycerol accumulated during the hyperosmotic treatment was used in the subsequent fermentation as a substrate, lessened the lag time, and consequently enhanced the fermentation ability. Various baker’s yeasts also showed a high leavening ability in dough after the hyperosmotic treatment.

Leavening ability of baker's yeast exposed to hyperosmotic media.

To develop a simple and rapid method for enhancing the leavening ability of baker's yeast, we examined the fermentation ability of baker's yeast exposed to hyperosmotic media. When baker's yeast cells were incubated at 25 degrees C for 1 h in a hyperosmotic medium containing 0.5% yeast extract, 0.5% peptone and 20% sucrose, the cells showed a higher fermentation ability in the subsequent fermentation test than those untreated. The increased ratios were from 40 to 60% depending on the strains used. Glucose and fructose showed a similar effect to that of sucrose, but sorbitol was less effective. A high correlation between the intracellular glycerol content and fermentation ability after the osmotic treatment suggested that glycerol accumulated during the hyperosmotic treatment was used in the subsequent fermentation as a substrate, lessened the lag time, and consequently enhanced the fermentation ability. Various baker's yeasts also showed a high leavening ability in dough after the hyperosmotic treatment.

Role of maltose permease and α-glucosidase in maltose fermentation and dough-leavening of Torulaspora pretoriensis YK-1

The yeast Torulaspora pretoriensis YK-1 possesses both high potential leavening ability and freeze-thaw resistance, but its leavening ability in dough, without the addition of sugar, is much less than commercial baking strains (Oda and Tonomura 1993) Institute for Fermentation, Osaka, Japan (IFO) 0022, another strain of T. pretoriensis , previously found to leaven dough efficiently without the addition of sugar, showed higher activities of both maltose permease and α -glucosidase and fermented maltose in an aqueous medium faster than YK-1. No significant difference was observed between the affinities of maltose permease and α -glucosidase from IFO 0022 and those from YK-1. MAL61 and MAL62 genes of Saccharomyces cerevisiae were expressed in T. pretoriensis YK-1 and elevated the activities of maltose permease and α -glucosidase, respectively, when these genes were introduced on YCp-type plasmids under control of the glyceraldehyde 3-phosphate dehydrogenase promoter. Maltose fermentation by cells harbouring the plasmids carrying either MAL61 or MAL62 genes was slightly stimulated. Introduction of both genes further enhanced the maltose fermentation rate but not leavening ability in dough without the addition of sugar. These results suggest that maltose permease and α -glucosidase determine the overall velocity of maltose fermentation.

Construction of a sucrose-fermenting bakers' yeast incapable of hydrolysing fructooligosaccharides

Fructooligosaccharides stimulate the growth of intestinal bifidobacteria which are related to the favorable health and nutrition of humans and other animals. Since the efficient amount of fructooligosaccharide for an adult human is relatively large (about 5 g per day), its addition to daily foods like bakery goods might be beneficial. However, commercial Bakers' yeast hydrolyses fructooligosaccharides by the action of invertase encoded in SUC genes and ferments the resulting monosaccarides. According to the findings that strains carrying the MAL-constitutive gene and lacking the SUC gene fermented sucrose and not fructooligosaccharide, we constructed a sucrose-fermenting strain, YOY920, incapable of hydrolysing fructooligosaccharide, by cross-breeding a baking strain and a laboratory strain. In a molasses medium, the cell yield of YOY920 was comparable to that of a baking strain FSC6001, and much higher than that of the non-sucrose-fermenting strains. Although fructooligosaccharide inhibited the dough leavening ability of YOY920, white bread containing fructooligosaccharide could be produced in the defined dough formula using the new strain.

Potassium oxide in California : Anon. ( Oil, Paint, and Drug Rep., Sept. 7, 1914)

The yeast Torulaspora pretoriensis YK-1 possesses both high potential leavening ability and freeze-thaw resistance, but its leavening ability in dough, without the addition of sugar, is much less than commercial baking strains (Oda and Tonomura 1993) Institute for Fermentation, Osaka, Japan (IFO) 0022, another strain of T. pretoriensis, previously found to leaven dough efficiently without the addition of sugar, showed higher activities of both maltose permease and α-glucosidase and fermented maltose in an aqueous medium faster than YK-1. No significant difference was observed between the affinities of maltose permease and α-glucosidase from IFO 0022 and those from YK-1. MAL61 and MAL62 genes of Saccharomyces cerevisiae were expressed in T. pretoriensis YK-1 and elevated the activities of maltose permease and α-glucosidase, respectively, when these genes were introduced on YCp-type plasmids under control of the glyceraldehyde 3-phosphate dehydrogenase promoter. Maltose fermentation by cells harbouring the plasmids carrying either MAL61 or MAL62 genes was slightly stimulated. Introduction of both genes further enhanced the maltose fermentation rate but not leavening ability in dough without the addition of sugar. These results suggest that maltose permease and α-glucosidase determine the overall velocity of maltose fermentation.