Glycerol production by fermenting yeast cells is essential for optimal bread dough fermentation.
ABSTRACT: Glycerol is the main compatible solute in yeast Saccharomyces cerevisiae. When faced with osmotic stress, for example during semi-solid state bread dough fermentation, yeast cells produce and accumulate glycerol in order to prevent dehydration by balancing the intracellular osmolarity with that of the environment. However, increased glycerol production also results in decreased CO2 production, which may reduce dough leavening. We investigated the effect of yeast glycerol production level on bread dough fermentation capacity of a commercial bakery strain and a laboratory strain. We find that ?gpd1 mutants that show decreased glycerol production show impaired dough fermentation. In contrast, overexpression of GPD1 in the laboratory strain results in increased fermentation rates in high-sugar dough and improved gas retention in the fermenting bread dough. Together, our results reveal the crucial role of glycerol production level by fermenting yeast cells in dough fermentation efficiency as well as gas retention in dough, thereby opening up new routes for the selection of improved commercial bakery yeasts.
Project description:Usually, aromatic yeasts are designed to ferment wheat substrates for baking purposes but identification of new substrates for these strains and consequently new formulations for dough could lead to diversified bakery products with improved nutritional qualities and specific sensorial properties. The purpose of our study was to optimize the fermentation of quinoa and amaranth flours with non-conventional yeast strains in order to obtain a preferment with high potential in enhancing nutritional, textural and sensorial features of white wheat bread. Two biotypes of <i>Saccharomyces cerevisiae</i> yeast-a wine yeast strain and a beer yeast strain-commercialized for their aromatic properties were used. Both aromatic yeast strains revealed good performance on fermenting pseudocereal substrates. Utilization of the obtained preferment in white wheat breadmaking led to bread with higher protein, fibres, mineral, total polyphenols content, with specific texture and aroma profile and high consumers' acceptability.
Project description:Saccharomyces cerevisiae is routinely used yeast in food fermentations because it combines several key traits, including fermentation efficiency and production of desirable flavors. However, the dominance of S. cerevisiae in industrial fermentations limits the diversity in the aroma profiles of the end products. Hence, there is a growing interest in non-conventional yeast strains that can help generate the diversity and complexity desired in today's diversified and consumer-driven markets. Here, we selected a set of non-conventional yeast strains to examine their potential for bread fermentation. Here, we tested ten non-conventional yeasts for bread fermentation, including two Saccharomyces species that are not currently used in bread making and 8 non-Saccharomyces strains. The results show that Torulaspora delbrueckii and Saccharomyces bayanus combine satisfactory dough fermentation with an interesting flavor profile. Sensory analysis and HS-SPME-GC-MS analysis confirmed that these strains produce aroma profiles that are very different from that produced by a commercial bakery strain. Moreover, bread produced with these yeasts was preferred by a majority of a trained sensory panel. These results demonstrate the potential of T. delbrueckii and S. bayanus as alternative yeasts for bread dough leavening, and provide a general experimental framework for the evaluation of more yeasts and bacteria.
Project description:Sourdough fermentation of bakery products is a well-established and widespread technique to confer an added value to the resulting food. In recent decades, gluten-free raw materials have gained more attention due to the diffusion of food disorders such as coeliac disease, but, at the same time, they present difficult manipulation and scarce technological properties because of the absence of gluten. For this reason, the present work was aimed at selecting starter cultures for sourdough application that are isolated from fermentation of sorghum flour. Three isolates of Lactobacillus fermentum, Weissella cibaria, and Weissella confusa were selected for the following properties: exopolysaccharide synthesis, acidification, CO2 production, and amylase activity. The investigated phenotypic characteristics were confirmed by genomic analyses, which also highlighted other potentially beneficial features for use in bakery products employment. These strains, together with bakery yeast, were used for bread preparation using sorghum and wheat flour and after 24 h of fermentation the resulting dough was analyzed to assess the improvement of its characteristics. The presence of lactic acid bacteria (LAB) had a great impact on the final dough, and the best preparation, from a rheological point of view, resulted in one made of sorghum and wheat flour with added LAB and bakery yeast, whose resulting characteristics were similar to all wheat flour doughs. The results of this study suggest a potential application of the selected starters in sorghum composite bread and should be validated with data from large-scale pilot tests conducted in industrial bakeries.
Project description:The behavior of yeast cells during industrial processes such as the production of beer, wine, and bioethanol has been extensively studied. In contrast, our knowledge about yeast physiology during solid-state processes, such as bread dough, cheese, or cocoa fermentation, remains limited. We investigated changes in the transcriptomes of three genetically distinct Saccharomyces cerevisiae strains during bread dough fermentation. Our results show that regardless of the genetic background, all three strains exhibit similar changes in expression patterns. At the onset of fermentation, expression of glucose-regulated genes changes dramatically, and the osmotic stress response is activated. The middle fermentation phase is characterized by the induction of genes involved in amino acid metabolism. Finally, at the latest time point, cells suffer from nutrient depletion and activate pathways associated with starvation and stress responses. Further analysis shows that genes regulated by the high-osmolarity glycerol (HOG) pathway, the major pathway involved in the response to osmotic stress and glycerol homeostasis, are among the most differentially expressed genes at the onset of fermentation. More importantly, deletion of HOG1 and other genes of this pathway significantly reduces the fermentation capacity. Together, our results demonstrate that cells embedded in a solid matrix such as bread dough suffer severe osmotic stress and that a proper induction of the HOG pathway is critical for optimal fermentation.
Project description:Identification of the yeast responsible for <i>Injera</i> fermentation is important in order to be more consistent and for scale-up of <i>Injera</i> production. In this study, yeast were isolated and identified from fermenting <i>teff</i> dough sample collected from household, hotels, and microenterprises, Addis Ababa. Initially, the yeast obtained from fermenting <i>teff</i> dough of different sources were selected on the basis of their CO<sub>2</sub> production potentials. Its DNA sequencing of isolated yeast identified <i>Pichia fermentans, Pichia occidentalis, Candida humilis, Saccharomyces cerevisiae,</i> and <i>Kazachstania bulderi.</i> The association of identified yeast to their sources indicated the presence of <i>Pichia fermentans</i> in fermenting dough samples collected from all sources whereas <i>Kazachstania bulderi</i>, <i>Saccharomyces cerevisiae,</i> and <i>Candida humilis</i> were shown to be present in samples collected from households, hotels, and microenterprises, respectively. The phenotypes and CO<sub>2</sub> production potentials of this yeast were also documented. This study has confirmed the presence of different yeast species in the fermentation of <i>teff</i> dough and hinted the complex nature of <i>Injera</i> dough fermentation.
Project description:Gene expression profiles of bakerâs yeast during initial dough-fermentation were investigated using liquid fermentation media to obtain insights at the molecular level into rapid adaptation mechanisms of bakerâs yeast. Results showed that onset of fermentation caused drastic changes in gene expression profiles within 15 min. Genes involved in the tricarboxylic acid (TCA) cycle were down-regulated and genes involved in glycolysis were up-regulated, indicating a metabolic shift from respiration to fermentation. Genes involved in ethanol production (PDC genes and ADH1), in glycerol synthesis (GPD1 and HOR2), and in low-affinity hexose transporters (HXT1 and HXT3) were up-regulated at the beginning of model dough-fermentation. Among genes up-regulated at 15 min, several genes classified as transcription were down-regulated within 30 min. These down-regulated genes are involved in messenger RNA splicing and ribosomal protein biogenesis, in zinc finger transcription factor proteins, and in transcriptional regulator (SRB8, MIG1). In contrast, genes involved in amino acid metabolism and in vitamin metabolism, such as arginine biosynthesis, riboflavin biosynthesis, and thiamin biosynthesis, were subsequently up-regulated after 30 min. Interestingly, the genes involved in the unfolded protein response (UPR) pathway were also subsequently up-regulated. Our study presents the first overall description of the transcriptional response of bakerâs yeast during dough-fermentation, and will thus help clarify genomic responses to various stresses during commercial fermentation processes. Experiment Overall Design: Saccharomyces cerevisiae T128 was used as a model of typical commercial bakerâs yeast used in Japan. After 18 h cultivation, cells in stationary phase were collected by centrifugation (2,700 ï g for 5 min). Some of the cell pellets were suspended in 900 ml of sterilized water. Cells for no-fermentation control were harvested after the fed-butch cultivation and stored until RNA extraction. Cell pellets (11,700 OD units) were suspended in 390 ml of lequid fermentation (LF) medium in a 500-ml flask and then fermented for 300 min. To investigate gene expression profiles during initial stages of dough-fermentation, cell samples for DNA microarray analysis were obtained from each culture medium at 15 min, 30 min, and 60 min. Cells in stationary phase were then collected by centrifugation (2,700ï g for 5 min), and stored until RNA extraction.
Project description:Steamed bread is a popular staple food in China. Jiaozi shows many advantages as a starter for dough fermentation and is frequently used for steamed bread production. The knowledge about the dough fermentation process using Jiaozi is helpful for production management and quality improvement of the final product. In this study, the applicability of Jiaozi for steamed bread production was investigated. Some important factors involved in dough fermentation were carefully examined and analyzed, including the evolution and diversity of major bacteria and fungi, acidity change, reducing sugar utilization, CO 2 production and retention, and different full dough fermentation periods. Combined with the quality evaluation of the final product, the results displayed that traditional Jiaozi was suitable as starter for steamed bread production using a two-stage procedure with a wide range of full fermentation time and also provided more insights into steamed bread production by Jiaozi.
Project description:The objective of this study was to unveil insights into the effects of <i>Saccharomyces cerevisiae</i> on the development of volatile compounds and metabolites during the dough fermentation in making Chinese steamed bread. Changes in gluten structure under the influence of baker's yeast were studied using scanning electron micrographs (SEM). A unique aroma profile was found comprising some previously reported aromatic compounds and some unreported aromatic aldehydes ((E)-2-Decenal and 2-Undecenal) and ketones (2-Heptanone and 2-Nonanone) in the baker's yeast fermentation. Among metabolites, the most preferred sugar for this yeast (glucose) showed a significant decrease in contents during the initial few hours of the fermentation and at last an increase was observed. However, most of the amino acids increased either slightly or decreased by the fermentation time. SEM of fermented dough showed that the yeast had a very little effect on starch stability. This study provided some fermentation features of the bakers' yeast which could be used for the tailored production of steamed bread.
Project description:Gene expression profiles of baker’s yeast during initial dough-fermentation were investigated using liquid fermentation media to obtain insights at the molecular level into rapid adaptation mechanisms of baker’s yeast. Results showed that onset of fermentation caused drastic changes in gene expression profiles within 15 min. Genes involved in the tricarboxylic acid (TCA) cycle were down-regulated and genes involved in glycolysis were up-regulated, indicating a metabolic shift from respiration to fermentation. Genes involved in ethanol production (PDC genes and ADH1), in glycerol synthesis (GPD1 and HOR2), and in low-affinity hexose transporters (HXT1 and HXT3) were up-regulated at the beginning of model dough-fermentation. Among genes up-regulated at 15 min, several genes classified as transcription were down-regulated within 30 min. These down-regulated genes are involved in messenger RNA splicing and ribosomal protein biogenesis, in zinc finger transcription factor proteins, and in transcriptional regulator (SRB8, MIG1). In contrast, genes involved in amino acid metabolism and in vitamin metabolism, such as arginine biosynthesis, riboflavin biosynthesis, and thiamin biosynthesis, were subsequently up-regulated after 30 min. Interestingly, the genes involved in the unfolded protein response (UPR) pathway were also subsequently up-regulated. Our study presents the first overall description of the transcriptional response of baker’s yeast during dough-fermentation, and will thus help clarify genomic responses to various stresses during commercial fermentation processes. Keywords: fermentation
Project description:In contemporary food production, an important role is given to the increase in the nutritional quality of foodstuff. In the bakery industry, one of the main cereals used is wheat flour (WF), which creates bread with proper sensory evaluation but is nutritionally poor. Soy-flour (SF) has increased nutrient content, and its consumption is recommended due to several health benefits. Dough fermentation with lactic acid bacteria (LAB) increases bread shelf life, improves flavor, and its nutritional quality, mostly due to its high organic acid production capability. In the present study, the addition of SF to WF, through fermentation with the cocultures of <i>Lactobacillus plantarum</i> and <i>Lactobacillus casei</i> was analyzed. Three different batches were performed by using WF supplemented with SF, as follows: batch A consisting of 90% WF and 10% SF; batch B-95% WF and 5% SF; batch C-100% WF. The fermentation with these two LABs presented several positive effects, which, together with increased SF content, improved the dough's rheological and physicochemical characteristics. The dynamic rheological analysis exhibited a more stable elastic-like behavior in doughs supplemented with SF (G' 4936.2 ± 12.7, and G? 2338.4 ± 9.1). Organic acid production changes were the most significant, especially for the lactic, citric, and tartaric content.