Growth Rate Of Yeast Research Articles

Spontaneous single-nucleotide substitutions and microsatellite mutations have distinct distributions of fitness effects.

The fitness effects of new mutations determine key properties of evolutionary processes. Beneficial mutations drive evolution, yet selection is also shaped by the frequency of small-effect deleterious mutations, whose combined effect can burden otherwise adaptive lineages and alter evolutionary trajectories and outcomes in clonally evolving organisms such as viruses, microbes, and tumors. The small effect sizes of these important mutations have made accurate measurements of their rates difficult. In microbes, assessing the effect of mutations on growth can be especially instructive, as this complex phenotype is closely linked to fitness in clonally evolving organisms. Here, we perform high-throughput time-lapse microscopy on cells from mutation-accumulation strains to precisely infer the distribution of mutational effects on growth rate in the budding yeast, Saccharomyces cerevisiae. We show that mutational effects on growth rate are overwhelmingly negative, highly skewed towards very small effect sizes, and frequent enough to suggest that deleterious hitchhikers may impose a significant burden on evolving lineages. By using lines that accumulated mutations in either wild-type or slippage repair-defective backgrounds, we further disentangle the effects of 2 common types of mutations, single-nucleotide substitutions and simple sequence repeat indels, and show that they have distinct effects on yeast growth rate. Although the average effect of a simple sequence repeat mutation is very small (approximately 0.3%), many do alter growth rate, implying that this class of frequent mutations has an important evolutionary impact.

The effect of maltodextrin edible coating containing pyracantha extract and potassium nano-carbonate on secondary metabolites, antioxidant capacity and microbiological properties of grape during cold storage

This study aimed to investigate the postharvest application of edible coating of maltodextrin containing potassium nanoparticles (KNPs; 0–2%) and pyracantha extract (PE; 0–1.5 %) on the maintenance of phenolic compounds, antioxidant capacity and microbial properties of ‘Rishbaba’ grape during 60 days at −1 °C using response surface methodology and central composite design. The results showed that the applied coating on Rishbaba grape maintained total phenol, total flavonoids, total anthocyanin, stilbenes (resveratrol and viniferin) and catechin. That also caused higher antioxidant capacity and lower mold and yeast growth in grape during the storage time. Finally, the best cold storage conditions of ‘Rishbaba’ grape were determined by using the edible maltodextrin coating containing 2 % KNPs and 1.5 % of PE for 34 days with a desirability of 0.728 in terms of investigated Characteristics. The optimized sample has the amount of total phenol (5.79 mg/g), total flavonoid (8.95 mg/g), total anthocyanin (6.48 mg/g) and the greatest ability to inhibit DPPH free radical (42.56 %) and the lowest growth rate of mold and yeast (21 Cfu/g).

Genetic modules for α-factor pheromone controlled growth regulation of Saccharomyces cerevisiae.

Saccharomyces cerevisiae is a commonly used microorganism in the biotechnological industry. For the industrial heterologous production of compounds, it is of great advantage to work with growth-controllable yeast strains. In our work, we utilized the natural pheromone system of S. cerevisiae and generated a set of different strains possessing an α-pheromone controllable growth behavior. Naturally, the α-factor pheromone is involved in communication between haploid S. cerevisiae cells. Perception of the pheromone initiates several cellular changes, enabling the cells to prepare for an upcoming mating event. We exploited this natural pheromone response system and developed two different plasmid-based modules, in which the target genes, MET15 and FAR1, are under control of the α-factor sensitive FIG1 promoter for a controlled expression in S. cerevisiae. Whereas expression of MET15 led to a growth induction, FAR1 expression inhibited growth. The utilization of low copy number or high copy number plasmids for target gene expression and different concentrations of α-factor allow a finely adjustable control of yeast growth rate.

The zinc finger motif in the mitochondrial large ribosomal subunit protein bL36m is essential for optimal yeast mitoribosome assembly and function

Ribosomes across species contain subsets of zinc finger proteins that play structural roles by binding to rRNA. While the majority of these zinc fingers belong to the C2-C2 type, the large subunit protein L36 in bacteria and mitochondria exhibits an atypical C2-CH motif. To comprehend the contribution of each coordinating residue in S. cerevisiae bL36m to mitoribosome assembly and function, we engineered and characterized strains carrying single and double mutations in the zinc coordinating residues. Our findings reveal that although all four residues markedly influence protein stability, C to A mutations in C66 and/or C69 have a more pronounced effect compared to those at C82 and H88. Importantly, protein stability directly correlates with the assembly and function of the mitoribosome and the growth rate of yeast in respiratory conditions. Mass spectrometry analysis of large subunit particles indicates that strains deleted for bL36m or expressing mutant variants have defective assembly of the L7/L12 stalk base, limiting their functional competence. Furthermore, we employed a synthetic bL36m protein collection, including both wild-type and mutant proteins, to elucidate their ability to bind zinc. Our data indicate that mutations in C82 and, particularly, H88 allow for some zinc binding albeit inefficient or unstable, explaining the residual accumulation and activity in mitochondria of bL36m variants carrying mutations in these residues. In conclusion, stable zinc binding by bL36m is essential for optimal mitoribosome assembly and function. MS data are available via ProteomeXchange with identifierPXD046465.

STUDY OF THE PROLIFERATIVE ACTIVITY OF SACCHAROMYCES CEREVISIAE IN YEAST BIOTECHNOLOGY AND PHYSICO-CHEMICAL METHODS OF ITS DETERMINATION

The article discusses the solution of issues related to increasing the efficiency of technological processes and ensuring the release of high-quality finished products, relevant for production based on the use of S. cerevisiae yeast. The paper identifies major reasons for the need to regulate yeast culture metabolism, considers existing practice and proposes methods of changing its metabolic activity. The purpose of the research is to create the classification of the supplements / preparations from different origin to improve yeast vital activity by adjusting its culture medium composition with the use of complex hierarchical faceted method.
 The proliferative processes taking place in the yeast cell are quite easily regulated. Therefore, knowing the dependence between the specific conditions of the environment and certain aspects of the yeast culture's vital activity, it is possible to purposefully change its growth, development and metabolism. Creating and maintaining certain conditions for the cultivation of yeast allows you to control the course of the fermentation process.
 The influence of biologically active substances on the proliferative activity of S. cerevisiae cells was investigated. Concentrations were determined and the regulatory effect of succinic and folic acid preparations on the proliferative activity of yeast cells was proven. A comparative analysis of influence of different concentrations of exogenous substances on microorganisms culture growth was carried out. The most optimal concentrations of drugs for activation of yeast cell division were determined: succinic acid/ascorbic acid – 0.0015/0.0002 mg/ml; folic acid – 0.006 mg/ml.
 Specific growth rate of yeast during cultivation in 20 % sucrose solution with succinic/ascorbic and folic acid preparations was calculated. It was established that the highest specific rate of cell growth was observed in the complex preparation, which included three organic acids. It was established that the specific rate of yeast reproduction in the complex preparation increased by an average of 30–35 % relative to the control sample. Increase in specific growth rate by 20–25 % of yeast was also observed in the medium with folic acid, the addition of succinic/ascorbic acids did not significantly increase specific rate (by approximately 10 %) of the growth of the S. cerevisiae yeast culture. It has been established that biologically active substances have certain concentrations that activate cell division and contribute to their active development and critical limits at which the development and growth of yeast cells are inhibited.

Factorizing polygenic epistasis improves prediction and uncovers biological pathways in complex traits

Epistasis is central in many domains of biology, but it has not yet been proven useful for understanding the etiology of complex traits. This is partly because complex-trait epistasis involves polygenic interactions that are poorly captured in current models. To address this gap, we developed a model called Epistasis Factor Analysis (EFA). EFA assumes that polygenic epistasis can be factorized into interactions between a few epistasis factors (EFs), which represent latent polygenic components of the observed complex trait. The statistical goals of EFA are to improve polygenic prediction and to increase power to detect epistasis, while the biological goal is to unravel genetic effects into more-homogeneous units. We mathematically characterize EFA and use simulations to show that EFA outperforms current epistasis models when its assumptions approximately hold. Applied to predicting yeast growth rates, EFA outperforms the additive model for several traits with large epistasis heritability and uniformly outperforms the standard epistasis model. We replicate these prediction improvements in a second dataset. We then apply EFA to four previously characterized traits in the UK Biobank and find statistically significant epistasis in all four, including two that are robust to scale transformation. Moreover, we find that the inferred EFs partly recover pre-defined biological pathways for two of the traits. Our results demonstrate that more realistic models can identify biologically and statistically meaningful epistasis in complex traits, indicating that epistasis has potential for precision medicine and characterizing the biology underlying GWAS results.

Isolation and characterization of glutathione S-transferase genes and their transcripts in Saccharina japonica (Laminariales, Phaeophyceae) during development and under abiotic stress

BackgroundGlutathione S-transferase (GST) is a crucial enzyme for metabolism, detoxification, and stress resistance in organisms. Many GSTs have been identified in seaweeds, but the isolation and functional analysis of GSTs in Saccharina japonica have not been completed.ResultIn this study, a total of 32 SjGST genes, localized on 10 scaffolds and 6 contigs, were identified and categorized into three groups. Most of these SjGSTs were presumed to be distributed in the cytoplasm. Tandem duplication had a significant influence on the expansion of the SjGST gene family. Functional analysis of cis-acting elements in the promoter regions demonstrated that SjGSTs enhance the stress resistance of the kelp. Quantitative real-time PCR tests confirmed that SjGSTs positively influence S. japonica sporophytes under stress from low salinity, drought, and high temperature. Recombinant yeast tests further affirmed the role of SjGSTs in stress resistance; SjGSTs improved the growth rate of recombinant yeast under 1.5 M NaCl or 8 mM H2O2. Analysis of biochemical parameters indicated that the optimum temperatures for SjGST20 and SjGST22 were 20 °C, and the optimum pH values were 7.0 and 8.0 for SjGST20 and SjGST22, respectively. The Km values for the substrate 1-chloro-2,4-dinitrobenzene (CDNB) were 2.706 mM and 0.674 mM and were 6.146 mM and 3.559 mM for the substrate glutathione (GSH) for SjGST20 and SjGST22, respectively.ConclusionSjGSTs are important stress resistant genes in S. japonica. This research results will enhance our understanding the function of GSTs in brown seaweeds, and explained its functional roles in stress resistance in marine environments.

Systematic profiling of dominant ubiquitin variants reveals key functional nodes contributing to evolutionary selection

Dominant-negative mutations can help to investigate the biological mechanisms and to understand the selective pressures for multifunctional proteins. However, most studies have focused on recessive mutant effects that occur in the absence of a second functional gene copy, which overlooks the fact that most eukaryotic genomes contain more than one copy of many genes. We have identified dominant effects on yeast growth rate among all possible point mutations in ubiquitin expressed alongside a wild-type allele. Our results reveal more than 400 dominant-negative mutations, indicating that dominant-negative effects make a sizable contribution to selection acting on ubiquitin. Cellular and biochemical analyses of individual ubiquitin variants show that dominant-negative effects are explained by varied accumulation of polyubiquitinated cellular proteins and/or defects in conjugation of ubiquitin variants to ubiquitin ligases. Our approach to identify dominant-negative mutations is general and can be applied to other proteins of interest.

Chemical Composition and Bioactivity of Laboratory-Fermented Bee Pollen in Comparison with Natural Bee Bread.

Bee bread is a valuable product obtained from the hive on a relatively small scale, while bee pollen is more easily available. Therefore, an effective laboratory method of converting pollen into a bee bread substitute is desired. The aim of the research was to verify the influence of selected factors (temperature, ultrasound) on the quality of obtained product using Lactobacillus rhamnosus inoculum. The composition of the fermented pollen was analyzed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Raman spectroscopy, and SDS-PAGE and compared to natural bee bread and the original pollen. In vitro biological activity was assessed as antioxidant activity using a yeast model (BY4741 and sod1∆ strains). Fermentation of pollen occurred spontaneously and after inoculation, as demonstrated by lower pH and higher lactic acid content. Raman spectroscopy and ICP-OES confirmed changes in composition compared to the initial pollen. Compared to bee bread, the fermented pollen showed a higher content of polyphenols and comparable antioxidant activity; moreover, it accelerated yeast growth rate. In addition, a protective effect was observed for Cu/Zn-superoxide dismutase 1 (sod1∆ yeast mutant exposed to hydrogen peroxide-induced oxidative stress). The higher fermentation temperature (25 °C) produces a more bee-bread-like product, while the use of ultrasound and starter culture seems to have no positive effect.

Water usability as a descriptive parameter of thermodynamic properties and water mobility in food solids

A classic problem in preservation is the microbes can grow in low-moisture foods. In this paper, the water sorption, and thermodynamic properties of glucose/WPI solid matrices were measured, while their molecular mobility was analyzed and associated with the microbial growth of D. Hansenii at various aw and 30 °C. Although the sorption isotherms, Tg, and relaxation processes of studied matrices were affected by aw and WPI, the microbial growth showed highly dependent on water mobility rather than aw. Hence, we introduced water usability (Uw), derived from the mobility difference between system-involved water and liquid pure water explicating from the classical thermodynamic viewpoint, to describe the dynamic changes of water mobility in glucose/WPI matrices. Despite to aw, the yeast growth rate was enhanced at high Uw matrices concomitantly with a rapid cell doubling time. Therefore, the proposed Uw provides a better understanding of the water relationships of microorganisms in food preservation.

Imaging of mtHyPer7, a Ratiometric Biosensor for Mitochondrial Peroxide, in Living Yeast Cells.

Mitochondrial dysfunction, or functional alteration, is found in many diseases and conditions, including neurodegenerative and musculoskeletal disorders, cancer, and normal aging. Here, an approach is described to assess mitochondrial function in living yeast cells at cellular and subcellular resolutions using a genetically encoded, minimally invasive, ratiometric biosensor. The biosensor, mitochondria-targeted HyPer7 (mtHyPer7), detects hydrogen peroxide (H2O2) in mitochondria. It consists of a mitochondrial signal sequence fused to a circularly permuted fluorescent protein and the H2O2-responsive domain of a bacterial OxyR protein. The biosensor is generated and integrated into the yeast genome using a CRISPR-Cas9 marker-free system, formore consistent expression compared to plasmid-borne constructs. mtHyPer7 is quantitatively targeted to mitochondria, has no detectable effect on yeast growth rate or mitochondrial morphology, and provides a quantitative readout for mitochondrial H2O2 under normal growth conditions and upon exposure to oxidative stress. This protocol explains how to optimize imaging conditions using a spinning-disk confocal microscope system and perform quantitative analysis using freely available software. These tools make it possible to collect rich spatiotemporal information on mitochondria both within cells and among cells in a population. Moreover, the workflow described here can be used to validate other biosensors.

Physiological and Molecular Characterization of Yeast Cultures Pre-Adapted for Fermentation of Lignocellulosic Hydrolysate

Economically feasible bioethanol process from lignocellulose requires efficient fermentation by yeast of all sugars present in the hydrolysate. However, when exposed to lignocellulosic hydrolysate, Saccharomyces cerevisiae is challenged with a variety of inhibitors that reduce yeast viability, growth, and fermentation rate, and in addition damage cellular structures. In order to evaluate the capability of S. cerevisiae to adapt and respond to lignocellulosic hydrolysates, the physiological effect of cultivating yeast in the spruce hydrolysate was comprehensively studied by assessment of yeast performance in simultaneous saccharification and fermentation (SSF), measurement of furaldehyde reduction activity, assessment of conversion of phenolic compounds and genome-wide transcription analysis. The yeast cultivated in spruce hydrolysate developed a rapid adaptive response to lignocellulosic hydrolysate, which significantly improved its fermentation performance in subsequent SSF experiments. The adaptation was shown to involve the induction of NADPH-dependent aldehyde reductases and conversion of phenolic compounds during the fed-batch cultivation. These properties were correlated to the expression of several genes encoding oxidoreductases, notably AAD4, ADH6, OYE2/3, and YML131w. The other most significant transcriptional changes involved genes involved in transport mechanisms, such as YHK8, FLR1, or ATR1. A large set of genes were found to be associated with transcription factors (TFs) involved in stress response (Msn2p, Msn4p, Yap1p) but also cell growth and division (Gcr4p, Ste12p, Sok2p), and these TFs were most likely controlling the response at the post-transcriptional level.

TORC1 and PKA activity towards ribosome biogenesis oscillates in synchrony with the budding yeast cell cycle.

Recent studies have revealed that the growth rate of budding yeast and mammalian cells varies during the cell cycle. By linking a multitude of signals to cell growth, the highly conserved target of rapamycin complex 1 (TORC1) and protein kinase A (PKA) pathways are prime candidates for mediating the dynamic coupling between growth and division. However, measurements of TORC1 and PKA activity during the cell cycle are still lacking. By following the localization dynamics of two TORC1 and PKA targets via time-lapse microscopy in hundreds of yeast (Saccharomyces cerevisiae) cells, we found that the activity of these pathways towards ribosome biogenesis fluctuates in synchrony with the cell cycle even under constant external conditions. Analysis of the effects of mutations of upstream TORC1 and PKA regulators suggests that internal metabolic signals partially mediate these activity changes. Our study reveals a new aspect of TORC1 and PKA signaling, which will be important for understanding growth regulation during the cell cycle.

Factors that cause replacement of shochu yeast by wild yeast upon Sashi-moto repetition

In shochu-making, a small amount of fermenting moromi is added to a koji/water mixture instead of yeast culture to initiate fermentation. This is a characteristic process called Sashi-moto. It is known that shochu yeast is replaced by wild yeast upon repetition of Sashi-moto. The shochu yeast strains Kagoshima No. 2 (K2), Kagoshima No. 4 (C4), and Kagoshima No. 5 (H5), but not Kagoshima No. 6 (A6), were replaced by wild yeast (strain No. S5-g). K2 and C4 were easily replaced compared to H5, and the specific growth rates of K2 and C4 were lower than that of S5-g under higher osmotic pressure. Although the specific growth rate of H5 was higher than that of S5-g, its yeast population at the stationary phase was smaller than S5-g. On the other hand, both the specific growth rate and yeast population of A6 were higher than those of S5-g. The specific growth rate of yeast would be affected by osmotic tolerance and specific characters of the yeast strain.

Development of the innovative biotechnological methods of the biological preparations production for feed purposes

The aim of this study was the production of the biological preparations based on the hydrolyzed pea flour and the yeast biomass. The research objects were Saccharomyces cerevisiae Y-1218 yeast with glucoamylase activity, pea flour, and Celloviridin S20X and Amyloprotoorizin S20X enzyme preparations (EP). The specific growth rate of the yeast was determined by the calculation method, protein content – via Kjeldahl and Lowry methods, reducing substances content – by Somogyi-Nelson assay, the amine nitrogen content – by the formol titration method, the number of living yeast cells – by sowing of dilutions. The amino acid content was measured on the KNAUER (Germany) high-performance liquid chromatograph. As the result of the studies, enzyme preparations for the fermentative processing of pea flour were selected. The cultivation conditions of the Saccharomyces cerevisiae Y-1218 yeast were opted. Under these chosen growing parameters the produced biomass contained 2.4×109 CFU/cm3 and specific growth rate of yeast was 0.264 h-1. The resulting biomass contained a high amount of essential amino acids. The biopreparations production based on the described ingredient is perspective. These biopreparations with increased biological value could be used for feed purposes.

Simulation and economic evaluation of different process alternatives for the fermentation and distillation steps of ethanol production

The intensification of climate change and other phenomena associated with the growing pollution of the planet have increasingly highlighted the need for energy sources that are less harmful to the environment. There is currently a strong trend towards the substitution of non-renewable and highly polluting energy sources, such as petroleum derivatives, by renewable sources, from the use of biomass, for example. Sugarcane is a widely used biomass for ethanol production in Brazil, which is the second largest ethanol producer in the world. Although well established in the country, ethanol production is very complex and process alternatives are continually being developed to make it more efficient. This work aims to simulate the fermentation and distillation stages of the ethanol production process from sugarcane juice, considering both the conventional route and alternative technologies, and compare them through an integrated economic analysis. In the simulations, the yeast growth rate in the fermenter was considered through the creation of a solid pseudocomponent, which is a differential of this work. For fermentation, the conventional route was compared with Low Temperature Fermentation and Vacuum Extractive Fermentation. For distillation, besides the conventional process, Double Effect Distillation was also analyzed. It was concluded that the process designs of Low Temperature Fermentation + Conventional Distillation and Vacuum Extractive Fermentation + Double Effect Distillation are economically advantageous when compared to the conventional one, with annual net profits up to 31.6% higher, showing the possibility of obtaining a more efficient and profitable process, or a reduction of up to 5% in the ethanol price through the implementation of these alternative technologies.

A Systematic Method to Explore Radio-Frequency Non-Thermal Effect on the Growth of Saccharomyces Cerevisiae

Radio frequency (RF) non-thermal (NT) bio-effects have been a subject of debate and attracted significant interests due to potential health risks or beneficial applications. In this work, we report a systematic method for broadband investigation of RF NT effects on <i>Saccharomyces cerevisiae</i> yeast growth. The method includes a transverse electro-magnetic (TEM) device and a dielectric spectroscopy technique for RF frequency selection. A stripline-based TEM device has two 240-<i>&#x03BC;</i>L chambers 3D printed for cell cultures. The fabricated device operates up to a few GHz and produces uniform RF fields for cell exposure testing. A vector network analyzer (VNA) was used to provide &#x2212;20 dBm continuous-wave (CW) RF power. The heating effects on cell growth were estimated to be negligible. Frequency regions, where large permittivity differences between the medium and yeast cultures were obtained and used to select RF testing frequencies, <i>e.g.,</i> 1.0 MHz, 3.162 MHz, 10 MHz. These differences may indicate RF field gradients near cell membrane, and the gradients may affect local nutrient transport. Additionally, RF at 905 MHz is tested for comparison purpose. Yeast cells in the exponential growth phase were examined at four RF frequencies and compared with two controls. One control device held at the same temperature as the test device, while the other control was held at a temperature 1 &#x00B0;C higher. The results showed that the RF fields at 3.162 MHz reduced yeast growth rates by 15.1&#x0025;; however, the RF fields at 1.0 MHz enhanced cell growth by 13.7&#x0025;, while the observed 4.3&#x0025; growth rate increase at 10 MHz is insignificant and the RF fields at 905 MHz had no effects on the cell growth. These results showed a clear RF NT effects on <i>S. cerevisiae</i> growth that was frequency dependent. The hypothesized mechanisms of these effects, i.e., non-uniform RF fields near cell membranes and fluidic diodes in cell membrane ion channels may play important roles in nutrient transport, need to be further investigated.

Application of Saccharomyces cerevisiae isolated from industrial effluent for zinc biosorption and zinc-enriched SCP production for human and animal

We aimed to optimize the culture condition for industrial effluent isolated Saccharomyces cerevisiae strains to reach the highest zinc biosorption, biomass, and protein production for human and animals. S. cerevisiae strains carrying ZRT and FET genes were isolated from effluent samples and identified using standard methods. Subsequently, the growth rate of yeasts in the presence of Zn2+, as well as the level of Zn2+ uptake by the yeast cells, were examined at 24-hour intervals. RT-PCR technique was applied to quantify the expression level of the target genes in yeast cells. The effect of the initial pH of culture medium was studied on the yeast growth rate, zinc absorption, and target genes expression. After setting the optimum pH, Kjeldahl method was applied for assessment of the total protein content of yeast cells. In the optimum conditions, S. cerevisiae showed the maximum growth rate, zinc uptake, and expression level of Zrt1 and Fet4. In addition, protein content of S. cerevisiae biomass in this optimum condition was above 50% (w/w). We demonstrated that S. cerevisiae species isolated from industrial effluents could be considered as highly promising candidates for producing Zn-enriched single cell protein. However, further research is believed to be required.

Biochemical processes during secondary fermentation of apple juice and storage of sparkling wines

Apple sparkling wines are characterized not only by the foamy and sparkling properties common to all wines of this type, but also by freshness and lightness of taste, which are the result of a harmonious combination of the taste qualities of fruit juice and its fermentation products against the background of low alcohol content and low oxidation. The aim of the study was to change the main physical and chemical parameters and the number of yeast cells during fermentation – deaeration and fermentation of apple juice and wine. The objects of research were winter varieties of apples Idared, Jonathan, Renet Simirenko, Florina, apple wine materials and finished wine. The chemical composition and quality of fruits and wine materials were determined according to generally accepted methods in winemaking. It has been established that during the day, the decrease in the R potential during deaeration of the fermentation mixture for apple cider occurs within the range of 8-20 mV, and the higher the initial potential, the more effective its reduction. In the first 3-5 days, a decrease in the R potential by an average of 50-71 mV was observed in all samples. Then the potential basically remained at this level without changes. Studies have shown that when fermenting natural fermented juice with freshly introduced wine yeast, the number of cells after 2 days increases by more than 2.7 times, and after 5 days – almost 4.5 times, reaching 31 million/ml. The most intensive reproduction of yeast is observed on the 2nd-3rd day of fermentation. At the same time, there is a sharp decrease of ammonia nitrogen, amine nitrogen and oxygen in the content. A decrease in the content of oxygen and peroxides, in turn, is accompanied by a significant decrease in the R potential of the fermenting must. After 5 days of fermentation, the number of yeast cells increases by 4.4 times with the full use of nitrogen nutrition, especially ammonia nitrogen, as well as oxygen. The increase in the initial alcohol content of the fermented juice to 8.5% vol. reduces the rate of yeast growth.

Comparative study on the growth rate and physico-chemical properties of yeast (Saccharomyces cerevisiae) using Zea mays l. (corn) and Triticum asetivum l. (wheat) flour substrates

Significance of yeasts in food technology as well as in human nutrition, as alternative sources of protein to cover the demands in a world of low agricultural production and rapidly increasing population, makes the production of food grade yeasts important. The comparative study on the growth rate and physicochemical properties of yeast was carried out using corn and wheat flour substrates. 50 g of wheat and corn flour each was weighed into a calibrated culture plastic rubber. 120 ml of distilled water was added with 5 ml of lemon juice. The sample was stirred and kept under room temperature at 26°C. The growth of the yeast were observed every three days for two weeks and recorded in millimetre. Yeast (Saccharomyces cerevisiae) culture grown using corn flour gave a mean growth of 12.18±0.38 for the first week and 15.24±1.21 for the second week. On the other hand, the growth of yeast produced from wheat flour gave 8.29±0.35 and 10.46±1.23 for first and second week respectively. The result also showed that yeast produced from corn flour grew rapidly than the wheat flour. The acid value of yeast produced from corn flour was 17.95 mgKOH/g, saponification value of 9.5 mgKOH/g, ester value of 164.37 mgKOH/g, iodine value of 87.63 gI2/100g, peroxide value of 16.0 mEq/kg, free fatty-acid of 9.02%, refractive index of 1.50, specific gravity of 0.902, density of 5 g/cm3 and pH of 5, while yeast produced from wheat flour had an acid value of 14.3 mgKOH/g, saponification value of 5.3 mgKOH/g, ester value of 152.1 mgKOH/g, iodine value of 66.0 gI2/100g, peroxide value of 10.1 mEq/kg, free fatty-acid of 5.2%, refractive index of 0.6, specific gravity of 0.561, density of 3.2 g/cm3 and pH of 5. The result showed that the physico-chemical properties of yeast produced from corn flour were higher than that produced from wheat flour with p value of 0.001.