Industrial Baker's Yeast Research Articles

Oxidative stability of cocoa hazelnut cream enriched with inactive yeast cells

The aim of the study was to evaluate the effect of inactivated yeast cells on the oxidative stability, color, and sensory properties of cocoa hazelnut cream. For this purpose, yeast cells were inactivated and added in the cocoa hazelnut cream. Glutathione content, antioxidant properties, TBARS, color, and sensory properties of the samples were examined during 150 days. According to the results, the GSH content in the cocoa hazelnut cream after yeast addition was 47.55 nmol GSH/g sample. In addition, TBARS value was lower in yeast-added sample (0.1846 mg MDA/kg sample) compared to control (0.2262 mg MDA/kg sample) at the end of storage. Moreover, the DPPH values of the hazelnut cream did not change with the yeast addition, significantly. However, yeast-added samples had higher FRAP, CUPRAC, and total phenolic content than the control sample. Sensory scores of yeast-added samples were also acceptable compared to control samples. Practical applications In this study, the effect of inactive industrial baker's yeast (Saccharomyces cerevisiae) addition on the functional and sensory properties of the cocoa hazelnut cream was investigated. The results have shown that industrial baker's yeast can be encapsulated by heat treatment and helps to maintain oxidative stability of cocoa hazelnut cream without causing significant changes in the sensory properties during storage. Thus, the addition of inactivate yeast cells can be recommended for the further development of novel and innovative nutritional products with natural ingredients.

Full Mass Balance Analysis During Industrial Baker's Yeast Fermentation Shows New Perspectives for Biomolecule Recovery

Abstract This study aims to partially compensate the lack of reliable data regarding full mass balance analysis during industrial baker's yeast fermentation and the chemical composition of the resu...

Turning industrial aerobic fermentation plants into thermal power stations

The industrial aerobic bioprocess of baker's yeast production requires large amounts of water to cool down large bubble column bioreactors. As result, an appreciable quantity of low-grade heat is generated. Because of the low temperature level of the water (~25°C) exiting the bioreactors cooling system, very little attention has been dedicated to heat recovery and conversion from this stream, which is usually released in rivers, streams, and canals. In this work, we simulated the generation of low-grade heat (up to 14.4 MW) from an industrial baker's yeast production plant consisting of seven 150-m3 bioreactors. Subsequently, a dedicated transcritical carbon dioxide heat pump system for the conversion of this low-grade heat into fourth generation district heat (~16.2 MW) was successfully designed. Fourth generation district heat employs low-temperature water (30-70°C) as heat carrier and is expected to play a major role in future sustainable energy system. Finally, an economic study confirmed the feasibility and the applicability of our approach and a concept for long-term energy storage including state-of-the-art phase change material (PCM)–units was discussed.

New trends in industrial baker's yeast fermentation: Recovery of key biomolecules and low-grade heat conversion

New trends in industrial baker's yeast fermentation: Recovery of key biomolecules and low-grade heat conversion

Industrial baker's yeast fermentation: From manufacture to integrated sustainability

A series of novel L-malic acid modified hyper-cross-linked resins were synthesized from macroporous chloromethylated styrene-divinylbenzene copolymer by Fridel–Crafts reaction and esterification reaction. The adsorption behavior of the resin toward p-aminobenzoic acid was investigated from aqueous solution. KZ-3 displayed the most outstanding adsorption capacity due to its proper surface structure and higher functional group utilization rate. Subsequently, the adsorption kinetic of p-aminobenzoic acid onto precursor resin Z-3, modified resin KZ-3 and commercially available polymeric adsorbent H-103 was compared. The result demonstrated that KZ-3 had the optimal adsorption capacity because of its hydrogen bonding driving force and hydrophilicity enhancement which brought by oxygen-containing functional groups. Especially, KZ-3 is 3 times higher than the precursor resin in terms of adsorption rate. Kinetic curves could be characterized by pseudo-second-order rate equation and both the intra-particle diffusion and the film diffusion were the rate-limiting steps. The isotherms could be fitted by Langmuir model and the adsorption was an exothermic, spontaneous and more ordered arrangement process due to its negative thermodynamic parameters.

Impact of Saccharomyces cerevisiae metabolites produced during fermentation on bread quality parameters: A review

ABSTRACTAlthough bread making with the use of Baker's yeast has a long tradition in human history, little attention has been paid to the connection between yeast addition and the final bread quality. Nowadays, bakers mainly use different flour additives such as enzymes (amylases, hemicellulases, and proteases) to change and improve dough properties and/or bread quality. Another strategy is the use of modified industrial Baker's yeast. To date, there is no yeast strain used in the baking industry, which is genetically modified, despite some studies demonstrating that the application of recombinant DNA technology is a possibility for improved strains suitable for baking. However, due to the fact that the majority of consumers in Europe highly reject the use of genetically modified microorganisms in the production of food, other strategies to improve bread quality must be investigated. Such a strategy would be a reconsideration of the selection of yeast strains used for the baking process. Next to the common criteria, the requirement for adequate gas production, more attention should be paid on how yeast impacts flavor, shelf life, color, and the nutritional value of baked products, in a similar way to which yeast strains are selected in the wine and brewing industries.

Development of intra-strain self-cloning procedure for breeding baker's yeast strains

Previously reported self-cloning procedures for breeding of industrial yeast strains require DNA from other strains, plasmid DNA, or mutagenesis. Therefore, we aimed to construct a self-cloning baker's yeast strain that exhibits freeze tolerance via an improved self-cloning procedure. We first disrupted the URA3 gene of a prototrophic baker's yeast strain without the use of any marker gene, resulting in a Δura3 homozygous disruptant. Then, the URA3 gene of the parental baker's yeast strain was used as a selection marker to introduce the constitutive TDH3 promoter upstream of the PDE2 gene encoding high-affinity cyclic AMP phosphodiesterase. This self-cloning procedure was performed without using DNA from other Saccharomyces cerevisiae strains, plasmid DNA, or mutagenesis and was therefore designated an intra-strain self-cloning procedure. Using this self-cloning procedure, we succeeded in producing self-cloning baker's yeast strains that harbor the TDH3p-PDE2 gene heterozygously and homozygously, designated TDH3p-PDE2 hetero and TDH3p-PDE2 homo strains, respectively. These self-cloning strains expressed much higher levels of PDE2 mRNA than the parental strain and exhibited higher viability after freeze stress, as well as higher fermentation ability in frozen dough, when compared with the parental strain. The TDH3p-PDE2 homo strain was genetically more stable than the TDH3p-PDE2 hetero strain. These results indicate that both heterozygous and homozygous strains of self-cloning PDE2-overexpressing freeze-tolerant strains of industrial baker's yeast can be prepared using the intra-strain self-cloning procedure,and, from a practical viewpoint, the TDH3p-PDE2 homo strain constructed in this study is preferable to the TDH3p-PDE2 hetero strain for frozen dough baking.

Enhanced leavening properties of baker's yeast by reducing sucrase activity in sweet dough.

Leavening ability in sweet dough is required for the commercial applications of baker's yeast. This property depends on many factors, such as glycolytic activity, sucrase activity, and osmotolerance. This study explored the importance of sucrase level on the leavening ability of baker's yeast in sweet dough. Furthermore, the baker's yeast strains with varying sucrase activities were constructed by deleting SUC2, which encodes sucrase or replacing the SUC2 promoter with the VPS8/TEF1 promoter. The results verify that the sucrase activity negatively affects the leavening ability of baker's yeast strains under high-sucrose conditions. Based on a certain level of osmotolerance, sucrase level plays a significant role in the fermentation performance of baker's yeast, and appropriate sucrase activity is an important determinant for the leavening property of baker's yeast in sweet dough. Therefore, modification on sucrase activity is an effective method for improving the leavening properties of baker's yeast in sweet dough. This finding provides guidance for the breeding of industrial baker's yeast strains for sweet dough leavening. The transformants BS1 with deleted SUC2 genetic background provided decreased sucrase activity (a decrease of 39.3%) and exhibited enhanced leavening property (an increase of 12.4%). Such a strain could be useful for industrial applications.

Effects of SNF1 on Maltose Metabolism and Leavening Ability of Baker's Yeast in Lean Dough.

Maltose metabolism of baker's yeast (Saccharomyces cerevisiae) in lean dough is negatively influenced by glucose repression, thereby delaying the dough fermentation. To improve maltose metabolism and leavening ability, it is necessary to alleviate glucose repression. The Snf1 protein kinase is well known to be essential for the response to glucose repression and required for transcription of glucose-repressed genes including the maltose-utilization genes (MAL). In this study, the SNF1 overexpression and deletion industrial baker's yeast strains were constructed and characterized in terms of maltose utilization, growth and fermentation characteristics, mRNA levels of MAL genes (MAL62 encoding the maltase and MAL61 encoding the maltose permease) and maltase and maltose permease activities. Our results suggest that overexpression of SNF1 was effective to glucose derepression for enhancing MAL expression levels and enzymes (maltase and maltose permease) activities. These enhancements could result in an 18% increase in maltose metabolism of industrial baker's yeast in LSMLD medium (the low sugar model liquid dough fermentation medium) containing glucose and maltose and a 15% increase in leavening ability in lean dough. These findings provide a valuable insight of breeding industrial baker's yeast for rapid fermentation.

Effects of MAL61 and MAL62 overexpression on maltose fermentation of baker’s yeast in lean dough

The predominant fermentable sugar in lean dough is maltose. To improve the leavening ability of baker's yeast in lean dough, maltose metabolism should be improved. Maltase (alpha-glucosidase, encoded by MAL62) and maltose permease (encoded by MAL61) are the major factors involved in maltose metabolism. The major rate-limiting factor in maltose metabolism and leavening ability of baker's yeast remains unclear. In this work, MAL61 and/or MAL62 overexpression strains were constructed to investigate the decisive factor for maltose metabolism of industrial baker's yeast in lean dough. Our results show that elevated maltose permease activity by MAL61 overexpression yielded less improvement in maltose fermentation compared to elevated maltase activity by MAL62 overexpression. Significant increase in maltase activity by MAL62 overexpression could result in a 44% increase in leavening ability of industrial baker's yeast in lean dough and a 39% increase in maltose metabolism in a medium containing glucose and maltose. Thus, maltase was the rate-limiting factor in maltose fermentation of industrial baker's yeast in lean dough. This study lays a foundation for breeding of industrial baker's yeast for quick dough leavening.

Improvement of stress tolerance and leavening ability under multiple baking-associated stress conditions by overexpression of the SNR84 gene in baker's yeast

During the bread-making process, industrial baker's yeast cells are exposed to multiple baking-associated stresses, such as elevated high-temperature, high-sucrose and freeze–thaw stresses. There is a high demand for baker's yeast strains that could withstand these stresses with high leavening ability. The SNR84 gene encodes H/ACA snoRNA (small nucleolar RNA), which is known to be involved in pseudouridylation of the large subunit rRNA. However, the function of the SNR84 gene in baker's yeast coping with baking-associated stresses remains unclear. In this study, we explored the effect of SNR84 overexpression on baker's yeast which was exposed to high-temperature, high-sucrose and freeze–thaw stresses. These results suggest that overexpression of the SNR84 gene conferred tolerance of baker's yeast cells to high-temperature, high-sucrose and freeze–thaw stresses and enhanced their leavening ability in high-sucrose and freeze–thaw dough. These findings could provide a valuable insight for breeding of novel stress-resistant baker's yeast strains that are useful for baking.

Enhancement of the proline and nitric oxide synthetic pathway improves fermentation ability under multiple baking-associated stress conditions in industrial baker's yeast

BackgroundDuring the bread-making process, industrial baker's yeast, mostly Saccharomyces cerevisiae, is exposed to baking-associated stresses, such as air-drying and freeze-thaw stress. These baking-associated stresses exert severe injury to yeast cells, mainly due to the generation of reactive oxygen species (ROS), leading to cell death and reduced fermentation ability. Thus, there is a great need for a baker's yeast strain with higher tolerance to baking-associated stresses. Recently, we revealed a novel antioxidative mechanism in a laboratory yeast strain that is involved in stress-induced nitric oxide (NO) synthesis from proline via proline oxidase Put1 and N-acetyltransferase Mpr1. We also found that expression of the proline-feedback inhibition-less sensitive mutant γ-glutamyl kinase (Pro1-I150T) and the thermostable mutant Mpr1-F65L resulted in an enhanced fermentation ability of baker's yeast in bread dough after freeze-thaw stress and air-drying stress, respectively. However, baker's yeast strains with high fermentation ability under multiple baking-associated stresses have not yet been developed.ResultsWe constructed a self-cloned diploid baker's yeast strain with enhanced proline and NO synthesis by expressing Pro1-I150T and Mpr1-F65L in the presence of functional Put1. The engineered strain increased the intracellular NO level in response to air-drying stress, and the strain was tolerant not only to oxidative stress but also to both air-drying and freeze-thaw stresses probably due to the reduced intracellular ROS level. We also showed that the resultant strain retained higher leavening activity in bread dough after air-drying and freeze-thaw stress than that of the wild-type strain. On the other hand, enhanced stress tolerance and fermentation ability did not occur in the put1-deficient strain. This result suggests that NO is synthesized in baker's yeast from proline in response to oxidative stresses that induce ROS generation and that increased NO plays an important role in baking-associated stress tolerance.ConclusionsIn this work, we clarified the importance of Put1- and Mpr1-mediated NO generation from proline to the baking-associated stress tolerance in industrial baker's yeast. We also demonstrated that baker's yeast that enhances the proline and NO synthetic pathway by expressing the Pro1-I150T and Mpr1-F65L variants showed improved fermentation ability under multiple baking-associated stress conditions. From a biotechnological perspective, the enhancement of proline and NO synthesis could be promising for breeding novel baker's yeast strains.

Simultaneous accumulation of proline and trehalose in industrial baker's yeast enhances fermentation ability in frozen dough

Freeze tolerance is a necessary characteristic for industrial baker's yeast because frozen-dough baking is one of the key technologies for supplying oven-fresh bakery products to consumers. Both proline and trehalose are known to function as cryoprotectants in yeast cells. In order to enhance the freeze tolerance of yeast cells, we constructed a self-cloning diploid baker's yeast strain with simultaneous accumulation of proline, by expressing the PRO1-I150T allele, encoding the proline-feedback inhibition-less sensitive γ-glutamyl kinase, and trehalose, by disrupting the NTH1 gene, encoding neutral trehalase. The resultant strain retained higher tolerance to oxidative and freezing stresses than did the single proline- or trehalose-accumulating strain. Interestingly, our results suggest that proline and trehalose protect yeast cells from short-term and long-term freezing, respectively. Simultaneous accumulation of proline and trehalose in industrial baker's yeast also enhanced the fermentation ability in the frozen dough compared with the single accumulation of proline or trehalose. These results indicate that baker's yeast that accumulates both proline and trehalose is applicable for frozen-dough baking.

Adaptive evolution of baker's yeast in a dough‐like environment enhances freeze and salinity tolerance

SummaryWe used adaptive evolution to improve freeze tolerance of industrial baker's yeast. Our hypothesis was that adaptation to low temperature is accompanied by enhanced resistance of yeast to freezing. Based on this hypothesis, yeast was propagated in a flour‐free liquid dough model system, which contained sorbitol and NaCl, by successive batch refreshments maintained constantly at 12°C over at least 200 generations. Relative to the parental population, the maximal growth rate (µmax) under the restrictive conditions, increased gradually over the time course of the experiment. This increase was accompanied by enhanced freeze tolerance. However, these changes were not the consequence of genetic adaptation to low temperature, a fact that was confirmed by prolonged selection of yeast cells in YPD at 12°C. Instead, the experimental populations showed a progressive increase in NaCl tolerance. This phenotype was likely achieved at the expense of others traits, since evolved cells showed a ploidy reduction, a defect in the glucose derepression mechanism and a loss in their ability to utilize gluconeogenic carbon sources. We discuss the genetic flexibility of S. cerevisiae in terms of adaptation to the multiple constraints of the experimental design applied to drive adaptive evolution and the technologically advantageous phenotype of the evolved population.

Antioxidant N-acetyltransferase Mpr1/2 of industrial baker's yeast enhances fermentation ability after air-drying stress in bread dough

During bread-making processes, yeast cells are exposed to multiple stresses. Air-drying stress is one of the most harmful stresses by generation of reactive oxygen species (ROS). Previously, we discovered that the novel N-acetyltransferase Mpr1/2 confers oxidative stress tolerance by reducing intracellular ROS level in Saccharomyces cerevisiae Σ1278b strain. In this study, we revealed that Japanese industrial baker's yeast possesses one MPR gene. The nucleotide sequence of the MPR gene in industrial baker's yeast was identical to the MPR2 gene in Σ1278b strain. Gene disruption analysis showed that the MPR2 gene in industrial baker's yeast is involved in air-drying stress tolerance by reducing the intracellular oxidation levels. We also found that expression of the Lys63Arg and Phe65Leu variants with enhanced enzymatic activity and stability, respectively, increased the fermentation ability of bread dough after exposure to air-drying stress compared with the wild-type Mpr1. In addition, our recent study showed that industrial baker's yeast cells accumulating proline exhibited enhanced freeze tolerance in bread dough. Proline accumulation also enhanced the fermentation ability after air-drying stress treatment in industrial baker's yeast. Hence, the antioxidant enzyme Mpr1/2 could be promising for breeding novel yeast strains that are tolerant to air-drying stress.

酵母の環境ストレス耐性（第３回）ストレス環境下における網羅的表現型解析とストレス耐性酵母の分子育種

Baker's yeast is exposed to various environmental stresses during its production and bread making. To clarify genes crucial for tolerance to these stresses, we performed genome-wide screenings of mutants that showed sensitivity or tolerance to stresses using a complete collection of deletion mutant strains of Saccharomyces cerevisiae. These screenings revealed genes crucial for tolerance to each stress. It is important to note that genes involved in the vacuolar acidification were indispensable for tolerance to multiple stresses. We applied the results of the screenings to select target genes for molecular breeding of stress-tolerant yeasts. Using so-called self-cloning technique, the target gene was disrupted or overexpressed in a derivative of an industrial baker's yeast strain. Results of the genetic modification suggested that this strategy was appropriate for breeding of stress-tolerant yeasts.

Dynamic Neural-Network-Based Model-Predictive Control of an Industrial Baker's Yeast Drying Process

This paper presents dynamic neural-network-based model-predictive control (MPC) structure for a baker's yeast drying process. Mathematical model consists of two partial nonlinear differential equations that are obtained from heat and mass balances inside dried granules. The drying curves that are obtained from granule-based model were used as training data for neural network (NN) models. The target is to predict the moisture content and product activity, which are very important parameters in drying process, for different horizon values. Genetic-based search algorithm determines the optimal drying profile by solving optimization problem in MPC. As a result of the performance evaluation of the proposed control structure, which is compared with the model based on nonlinear partial differential equation (PDE) and with feedforward neural network (FFN) models, it is particularly satisfactory for the drying process of a baker's yeast.

Substrate inhibition kinetics of Saccharomyces cerevisiae in fed-batch cultures operated at constant glucose and maltose concentration levels

Fed-batch culture is the mode of operation of choice in industrial baker's yeast fermentation. The particular mode of culture, operated at stable glucose and maltose concentration levels, was employed in this work in order to estimate important kinetic parameters in a process mostly described in the literature as batch or continuous culture. This way, the effects of a continuously falling sugar level during a batch process were avoided and therefore the effects of various (stable) sugar levels on growth kinetics were evaluated. Comparing the kinetics of growth and the inhibition by the substrate in cultures grown on glucose, which is the preferential sugar source for Saccharomyces cerevisiae, and maltose, the most common sugar source in industrial media for baker's yeast production, a milder inhibition effect by the substrate in maltose-grown cells was observed, as well as a higher yield coefficient. The observed sugar inhibition effect in glucostat cultures was taken into account in modeling substrate inhibition kinetics. The inhibition coefficient Ki increased with increasing sugar concentration levels, but it appeared to be unaffected by the type of substrate and almost equal for both substrates at elevated concentration levels.

Production of rhizobia biofertilizers using baker's yeast effluent and their application to Leucaena leucocephala

Industrial baker's yeast effluent (BYE) was experimented on as a culture medium for growth and biomass production of six fast-growing rhizobia strains. Diluting the effluent with distilled water was necessary to maximize bacterial biomass production. The addition of phosphate buffer, ammonium chloride or trace-elements did not improve the final biomass yield of tested micro-organisms. Rhizobial growth and biomass on the effluent were comparable to traditional yeast extract mannitol medium (YEM). The Rhizobium spp. biomass, produced using either YEM or BYE, was evaluated as inoculum for Leucaena leucocephala (Lam.) de Wit in a pot experiment. No significant differences were reported in respect of legume nodule and growth parameters. Simultaneous inoculation with rhizobia and a group of associative diazotrophs supported better nodulation and nitrogenase activity.

Heterologous Expression of Type I Antifreeze Peptide GS-5 in Baker's Yeast Increases Freeze Tolerance and Provides Enhanced Gas Production in Frozen Dough

The demand for frozen-dough products has increased notably in the baking industry. Nowadays, no appropriate industrial baker's yeast with optimal gassing capacity in frozen dough is, however, available, and it is unlikely that classical breeding programs could provide significant improvements of this trait. Antifreeze proteins, found in diverse organisms, display the ability to inhibit the growth of ice, allowing them to survive at temperatures below 0 degrees C. In this study a recombinant antifreeze peptide GS-5 was expressed from the polar fish grubby sculpin (Myoxocephalus aenaeus) in laboratory and industrial baker's yeast strains of Saccharomyces cerevisiae. Production of the recombinant protein increased freezing tolerance in both strains tested. Furthermore, expression of the GS-5 encoding gene enhanced notably the gassing rate and total gas production in frozen and frozen sweet doughs. These effects are unlikely to be due to reduced osmotic damage during freezing/thawing, because recombinant cells showed growth behavior similar to that of the parent under hypermosmotic stress conditions.