Yeast Cake Research Articles

IDENTIFICATION OF YEAST STRAINS AND FILAMENTOUS FUNGI IN THE HAI HAU TRADITIONAL ALCOHOL YEAST CAKE

This study aims to determine the various strains of yeast and filamentous fungi in traditional alcohol yeast cake from Hai Hau district, Nam Dinh province. By traditional laboratory techniques such as isolation on YPD agar, observation of colony morphology as well as cell characteristics by microscopy, combined with molecular biology method to sequence ITS region 03 strains of yeast Saccharomyces cerevisiae CN1, CN2, and NM3 were identified: 01 pseudo-strain yeast Saccharomycopsis fibuligera NM02 and 01 strain of filamentous fungi Rhizopus microsporus NS04. The density of yeast strains cultured on YPD agar supplemented with 50 mg/L Tetracycline was 4.5 × 108 CFU/g, while the density of R. microsporus NS04 filamentous fungi was 2.0 × 106 CFU/g. With the agar plate diffusion method, yeast strains of S. cerevisiae CN1, CN2, and NM3 that are unable to biosynthesize extracellular enzymes have been identified. Yeast pseudo-strain S. fibuligera NM02 is capable of producing amylase (with starch substrate hydrolysis ring diameter > 9 mm), cellulase (16 mm), and protease (18 mm). The filamentous fungi R. microsporus NS04 has a higher ability to produce extracellular enzymes such as amylase (> 9 mm), cellulase (33 mm), and protease (39 mm)

Direct observation of the microfiltration of yeast cells at the micro-scale: Characterization of cake properties

This study examines the accumulation of yeast cells at the membrane surface and the morphology of the formed cake through microscale monitoring and analysis of the microfiltration process. An original dead-end microfiltration device with a model membrane was designed and coupled with an optical imaging system to provide direct observation from the side, allowing in-situ real time study of the filtration operation (Valencia et al. 2020 [1]). Here, the deposition of yeast cells, monodispersed and polydispersed particles, in the same size range that yeast cells, was analyzed. Image processing was used to perform a quantitative characterization of cake morphological properties in terms of height, porosity, permeability, Kozeny coefficient and specific resistance. The cakes formed by monodispersed spherical and non-spherical rigid particles exhibit a similar incompressible behavior with higher porosity than yeast cakes, with mean porosity values of 0.38 for the rigid particles and 0.15 for the yeast at the end of the filtration run, respectively. The cake obtained by the microfiltration of a model suspension of polydispersed particles close to yeast size and shape is more compact (porosity of 0.29) and less permeable. However, polydispersity does not fully explain yeast cake properties, in particular its compressibility. Indeed, the yeast cake has a high compressibility index n = 1.1, which is reflected in a significant volume expansion of the yeast cake after transmembrane pressure was removed.

Evaluating the performance and profitability of varied combinations of brewery by-products for fattening pigs

Context The consumption of pork is rapidly increasing in Uganda and presents an opportunity for pig farmers to maximise profits. However, the population and productivity of pigs remains low and this is attributed to the high cost of commercial feeds. Aims We aimed to evaluate the effects of various combinations of brewery by-products on the performance, carcass characteristics and profitability of fattening pigs. Methods The study involved 48 crossbred (Large White × Camborough) pigs weaned at 2 months of age and weighing 10.3 ± 1.2 kg. Group pens of four pigs, balanced for sex and weight, were assigned in a completely randomised design with three replications to four diets: BYM, 22% brewers’ spent grain + 15% yeast cake + 60% malt dust; BY, 33% brewers’ spent grain + 14% yeast cake (with 50% maize bran); YM, 27% yeast cake + 70% malt dust; and a commercial diet (control). Feed intake and efficiency, costs and carcass characteristic were determined. Key results Feeding brewery by-products increased (P < 0.05) average daily feed intake by 1.40, 1.11, 1.09 kg/day for BYM, BY and YM compared with the control diet. Pigs fed the control diet had better (P < 0.05) feed efficiency (feed conversion ratio 3.4) than those fed BYM (6.6), BY (5.7) and YM (6.1). The unit cost of diets (Ugandan shillings, USh) increased in the order BYM (USh410) < YM (USh439) < BY (USh551) < commercial diet (USh1313). The unit cost of producing meat increased in the order YM (USh2691) < BYM (USh2713) < BY (USh3150) < commercial diet (USh5331). The highest gross margins accrued from BYM (USh36 769), followed by YM (USh34 853), whereas a loss of USh41 735 was incurred when feeding the commercial diet. Dressing percentage and organ yield were comparable across diets (P > 0.05). Backfat thickness measured at four sites was similar (P > 0.05) across dietary treatments. Conclusion A blended mixture of brewery by-products containing brewers’ spent grain (22%), yeast (15%) and malt dust (60%) is an economical replacement of commercial diets for fattening pigs. Implications Brewery by-products can be used to increase profit margins without affecting the carcass characteristics of pigs.

Yeast Cell Cake Characterization in Alcohol Solution for Efficient Microfiltration.

Microfiltration is widely used to remove microbial cells from the fermentation broth in the downstream processing of biotechnological products. Because filtration behaviors are strongly affected by the characteristics of the microbial cell cake formed on the surface of the membrane, insights into the cake structure facilitate the design and operation of filter equipment and membranes. In the alcohol fermentation process using a yeast strain, the cake characteristics are considered to be complicated because yeast cells are strongly influenced by external factors such as filtration pressure and alcohol concentration. In this study, we evaluated the membrane filtration properties, in particular the cake characteristics of a yeast suspension containing alcohol. Microfiltration experiments were performed in the dead-end filtration mode using yeast suspensions with several ethanol concentrations (0–20 wt%) under constant pressure. Flux decline behaviors caused by yeast cake were put in a similar form for 0–15 wt% ethanol concentrations. In contrast, a severe flux decline was observed for the suspension with 20 wt% ethanol concentration. It was also observed that in the membrane filtration of yeast cells with 20 wt% ethanol concentration, the cake structure became denser and the filtration resistance remarkably increased because of cellular destruction. Furthermore, the yeast cake exhibited a high compressibility in the solution containing a 20 wt% ethanol concentration. Therefore, the filtration rate of the alcoholic fermentation broth is not significantly improved by increased pressure due to the increase in the cake resistance.

The rationale of selecting pastries to be made with waxy wheat flour

Analysis of the distinctive characteristics of various pastries has proved relevance of the differentiation approach (practiced outside Ukraine) to the technological properties of flour in producing specific product groups in Ukraine. The study shows the expediency of using non-amylose waxy wheat flour to stabilize the quality of pastries. The study of the technological properties of waxy wheat flour and characteristics of its starch composition has predetermined the choice of pastries with different textures – yeast pastries and honeybread cookies compatible with this type of flour. It has been found that the use of waxy wheat flour in the technology of yeast cakes improves the quality of finished products. A non-amylose type of flour instead of wheat flour in making low-sugar biscuits results in higher consumption characteristics in comparison with the standard, even when sugar is completely excluded from the recipe. The study of changes in the quality of no-bakeand boiled honeybread cookies in storage shows that the use of non-amylose flour facilitates preserving the honeybread cookies’ freshness, which is evidenced by a lower crystallinity of starch in no-bake honeybreads based on waxy wheat flour as well as less intensive weight loss in boiled honeybread cookies and higher crumbliness of the latter compared to the standard.

Model development for estimating microfiltration performance of bio-ethanol fermentation broth

A membrane process is used for bio-ethanol purification from fermentation broths. Yeast cells are separated from a suspension containing yeast, glucose and ethanol using cross-flow microfiltration. Yeast cells are retained by the filter membrane with a mean pore size of 0.45μm and recycled back into the broth, while most of the glucose and ethanol penetrate through the membrane into the filtrate. The operating condition effects, such as cross-flow velocity and transmembrane pressure, on the filtration flux, cake properties and solute rejections are measured and analyzed. The filtration flux increases over 2-fold as the cross-flow velocity increases from 0.1 to 0.5m/s and increases 50% as the transmembrane pressure is increased from 20 to 100kPa at a fixed cross-flow velocity of 0.5m/s. The experimental data show that the filter cake plays the major role in determining the filtration resistance. The yeast cake exhibits a specific filtration resistance as high as 1014m/kg and a compressibility of 0.55. The glucose and ethanol rejections are both lower than 8% and increase slightly with increasing cross-flow velocity or transmembrane pressure. The cake formation and solute rejections are analyzed theoretically using a force balance model for particle deposition and the standard capture equation for depth filtration. Semi-empirical equations are derived and used for predicting the filtration flux, cake thickness and solute rejection directly from the operating conditions. The calculated results using the proposed models agree fairly well with the experimental data.

Study of the separation of yeast by microsieves: In situ 3D characterization of the cake using confocal laser scanning microscopy

In situ 3D characterization of Aquamarijn microsieves fouling was achieved using Confocal Laser Scanning Microscopy (CLSM). A filtration chamber allowing direct microscopic observation of microbial cell deposition and cake characterization, specially designed for in situ observations, was used. Fluorescent dyed Saccharomyces cerevisiae yeast suspensions were filtered through 0.8μm and 2μm pore diameters silicon nitride microsieves under constant flow rate. The on-line yeasts deposition was recorded and the cake construction was followed layer by layer. Based on the 3D image processing, cake properties (particle arrangement, homogeneity, thickness and porosity). The compressibility of the yeast cake was analyzed. Finally, cake removal efficiency was also studied during microsieve cleaning operation.

Modeling the influence of slurry concentration on Saccharomyces cerevisiae cake porosity and resistance during microfiltration

Filtration of an isotonic suspension of baker's yeast through a 0.45-μm membrane was studied at two different pressures, 40 and 80 kPa, for yeast concentrations ranging from 0.14 to 51 kg/m(3) (dry weight). For a yeast volume fraction above 0.06 (~21.8 kg/m(3) ), the porosity of the yeast cake is less dependent on the suspension concentration. For highly diluted suspensions, the specific cake resistance approaches a minimum that depends on the filtration pressure. Correlation functions of cake porosity and specific cake resistance were obtained for the concentration range investigated showing that the Kozeny-Carman coefficient increases when the applied pressure increases. Both filtration pressure and slurry concentration can be process controlled. In the range of moderate yeast concentration, the filtrate flux may be increased by manipulating the filtration pressure and the slurry concentration, thereby improving the overall process efficiency. The complex behavior of yeast cakes at high slurry concentration can be described by a conventional model as long as part of yeast cells are assumed to form aggregates, which behave as single bigger particles. The aggregation effect may be accounted for using a binary mixture model.

Filtration characteristics of hollow fiber microfiltration membranes used in a specific double membrane bioreactor

The performance of the microfiltration in a specifically designed membrane bioreactor operating under various transmembrane pressures with periodic backwashing was investigated for model media. These media were representative of some usual components of a fermentation medium: BSA solution (2 g L −1), yeast suspension (8 g L −1, dry mass) and a mixture of BSA/yeast (2 g L −1/8 g L −1). In this system, the separation was provided by a 0.1 μm polysulfone hollow fiber membrane. The net permeate fluxes observed for yeast/BSA mixture were proportional to the transmembrane pressure applied (Δ P) but were less than those obtained with water osmosis, showing that, in spite of the periodic backwash, a small amount of irreversible fouling remained. This fouling can be assumed to be due to internal fouling by protein and/or external fouling by a residual yeast cake. Moreover, the net permeate flux obtained with the yeast/BSA mixture was higher than that obtained with the BSA alone, showing that a thin yeast cake probably acted as a primary filtration layer that could protect the polysulfone membrane against protein fouling. These experiments enable operating recommendations to be made for the use of this specific bioreactor concerning the transmembrane pressure value and the possible addition of inert particles.

Effects of Operating Conditions on the Purification of Protein in Centrifugal Filtration of Bio-Suspensions

The purification of BSA from yeast/BSA binary suspension using batchwise centrifugal filtration under various conditions is studied. Effects of suspension pH and rotational speed on the cake properties, filtration rate and protein recovery are discussed. The experimental results indicate that the filtration rate is significantly affected by the cake growth at the initial periods of filtration, and no evident rate difference can be found among different suspension pH values under a low rotational speed. However, the effect of cake compression becomes more dominant as rotational speed increases. The compression of yeast cake is irreversible and strongly affected by the suspension pH especially under a high rotational speed. The cakes formed at pH 3.0 possess the highest compressibility due to the yeast coagulation, while the average specific resistance of cake is the lowest at pH 7.0 because of the high zeta potential of yeast cells. In addition, the recovery of BSA can be as high as 95–98% under the operating conditions of this study. Since the BSA concentration in the filtrate keeps constant during the filtration under various rotational speeds, the recovery of BSA is dependent solely on the filtration rate in spite of the little adsorbed amount on the yeast cells. To operate under higher rotational speed and pH 7.0 is optimal from the viewpoint of economic operation time and protein recovery.

Effects of Human Deafness γ-Actin Mutations (DFNA20/26) on Actin Function

Six point mutations in non-muscle gamma-actin at the DFNA20/26 locus cause autosomal dominant nonsyndromic hearing loss. The molecular basis for the hearing loss is unknown. We have engineered each gamma-actin mutation into yeast actin to investigate the effects of these mutations on actin function in vivo and in vitro. Cells expressing each of the mutant actins as the sole actin in the cell were viable. Four of the six mutant strains exhibited significant growth deficiencies in complete medium and an inability to grow on glycerol as the sole carbon source, implying a mitochondrial defect(s). These four strains exhibited abnormal mitochondrial morphology, although the mtDNA was retained. All of the mutant cells exhibited an abnormally high percentage of fragmented/non-polarized actin cables or randomly distributed actin patches. Five of the six mutants displayed strain-specific vacuole morphological abnormalities. Two of the purified mutant actins exhibited decreased thermal stability and increased rates of nucleotide exchange, indicative of increased protein flexibility. V370A actin alone polymerized abnormally. It aggregated in low ionic strength buffer and polymerized faster than wild-type actin, probably in part because of enhanced nucleation. Mixtures of wild-type and V370A actins displayed kinetic properties in proportion to the mole fraction of each actin in the mixture. No dominant effect of the mutant actin was observed. Our results suggest that a major factor in the deafness caused by these mutations is an altered ability of the actin filaments to be properly regulated by actin-binding proteins rather than an inability to polymerize.

Reversibility of heterogeneous deposits formed from yeast and proteins during microfiltration

Formation of heterogeneous deposits of particulates and macromolecules occurs frequently during membrane filtration. Removal of these deposits is important in maintaining flux and preventing retention of valuable species. In this paper, the effect of interaction between bovine serum albumin (BSA) and yeast particles on the reversibility of cake formation during microfiltration was studied. Critical flux and hysteresis of flux–transmembrane pressure curves are evaluated using flux stepping experiments. Intermittent filtration was used to observe cake dispersal and re-establishment. Washed yeast formed reversible, low resistance cakes even above the apparent critical flux. At a low yeast concentration of 0.3 g/L, the introduction of 1 g/L protein into the feed solution reduced the apparent critical flux significantly. However, at higher concentrations of yeast (0.8 and 1.45 g/L), the introduction of protein had little effect on the apparent critical flux. It was observed that even 0.1 g/L BSA was sufficient to introduce irreversibility in the cake formation with 0.8 g/L yeast. The rate of fouling appeared lowest for pH 3.0 for these mixed systems, suggesting that rapid binding of BSA at the top of the cake due to electrostatic attraction prevented further penetration of the particles into the void space of the yeast cakes.

Microfiltration of protein-cell mixtures with crossflushing or backflushing

Crossflow microfiltration experiments were performed with and without crossflushing or backflushing using yeast suspensions, bovine serum albumin (BSA) solutions, and mixtures of yeast and BSA. Scanning electron microscope (SEM) photographs of the membrane surface were taken before and after crossflushing and backflushing. Backflushing is highly effective, while crossflushing is partially effective, in removing the external cake formed during filtration of yeast suspensions. Crossflushing is completely ineffective and backflushing is only partially effective for removal of internal foulants during filtration of BSA solutions. During backflushing or crossflushing of yeast–BSA mixtures, complete or partial removal of the yeast cake reduces the hydraulic resistance to permeate flow. However, this removal also exposes the primary membrane to internal fouling by BSA, against which neither crossflushing nor backflushing is very effective.

Two new anamorphic yeasts: Candida germanica and Candida neerlandica.

Descriptions are given for the two new anamorphic ascomycetous yeasts Candida germanica (type strain NRRL Y-27064, CBS 4105) and Candida neerlandica (type strain NRRL Y-27057, CBS 434). The species were isolated, respectively, from the atmosphere over Germany and from pressed yeast cake in The Netherlands. Phylogenetic analysis of 26S domain D1/D2 ribosomal DNA sequences places C. germanica near Pichia philogaea, whereas C. neerlandica is a member of the Lodderomyces elongisporus/Candida albicans clade.

Modeling of fouling reduction by secondary membranes

The external cake of rejected particles plays an important role in filtration processes, often influencing the permeation rates of all species. It may have higher resistance to the permeate flow than the clean membrane itself, but it may also act as a secondary or dynamic membrane which screens the primary membrane from the more strongly fouling species of smaller size. The screening process due to the presence of the secondary membrane is modeled for filtration of a bidisperse suspension of large and small particles. The large particles form an external cake on the surface of the primary membrane, which then acts as a deep-bed filter and captures some of the small particles and prevents them from fouling the primary membrane. The theory predicts an optimum concentration of the large particles which maximizes the permeate volume for a given duration of filtration. To test the model, cross-flow microfiltration experiments were done with yeast suspensions, protein solutions, and yeast–protein mixtures using cellulose acetate membranes. During filtration of yeast–protein mixtures, protein aggregates were captured or screened by the yeast cake, which reduced fouling of the primary membrane by the protein aggregates. Under optimum conditions, the presence of yeast increased the total permeate volume by two fold.

Effects of added yeast on protein transmission and flux in cross-flow membrane microfiltration

Microfiltration membranes may be used to separate valuable proteins from suspensions containing cells or cell debris. Although a clean microfiltration membrane allows for complete protein transmission and high flux, both of these quantities decline in time due to membrane fouling. Using bovine serum albumin (BSA) as a model protein, flux and protein transmission during cross-flow microfiltration were studied with and without added yeast cells. Cross-flow microfiltration of BSA-only solutions results in a BSA fouling layer with low permeability forming on the membrane surface. Due to this layer, the long-term BSA transmission is typically only 25-40%. In contrast, during microfiltration of yeast-BSA mixtures, the yeast forms a cake layer on the membrane surface. The yeast cake acts as a dynamic or secondary membrane, allowing BSA monomers to pass through but preventing protein aggregates from fouling the membrane. The result is slower flux decline and higher long-term BSA transmission of typically 60-90%. For filtration of yeast-BSA mixtures at low yeast concentrations (<1 g/L), 50-100% higher BSA recovery is obtained than for BSA-only solutions with the same BSA concentration. At high yeast concentrations (>5 g/L), the protein transmission remains high, but the recovery may be lower due to reduced flux.

Microfiltration of protein mixtures and the effects of yeast on membrane fouling

The effects of yeast cells on membrane fouling by a protein mixture were studied in dead-end filtration. A 0.2 μm cellulose acetate membrane was used with a 1 g/l protein mixture consisting of equal amounts of bovine serum albumin, lysozyme, and ovalbumin. Yeast cells were used either in suspension or as preformed yeast cakes on top of the membrane. A small concentration of 0.022 g/l yeast cells in suspension enhanced the permeate flux and maintained protein transmission at nearly 100%, compared with a 60% reduction in the protein concentration in the permeate obtained after 3 h for the protein mixture filtered alone. Higher suspended yeast concentrations of 0.043 and 0.18 g/l resulted in lower fluxes and intermediate values for the protein transmission. For the three different thicknesses of preformed yeast cakes studied (0.025, 0.05, and 0.10 cm), the cake with intermediate thickness resulted in protein transmission of nearly 100% and the highest permeate flux. The thinner yeast cake resulted in a lower permeate flux, but it maintained protein transmission at nearly 100%, whereas the thicker cake resulted in a reduction in both permeate flux and protein transmission. The mechanism proposed to explain the results is based on the formation of a secondary membrane by the yeast cells on top of the original membrane. This secondary membrane entraps protein aggregates, which would otherwise cause membrane fouling and reductions in permeate flux and protein transmission.

Ultrasonic Measurement of Local Concentration of Cake on Microfiltration Membrane Using Polymer Transducer.

In order to understand the filtration mechanism in microfiltration, information concerning cake concentration is important because the cake reduces the permeation rate. In this work, an ultrasonic measurement method of local cake concentration on the microriltration membrane was developed by using a special array polymer transducer. This method was applied to microliltration both with suspensions of yeast and polystyrene particles to study the effect of solidity of solute on cake compression. As a result, it was found that the yeast cake was compressible but that of polystyrene particles incompressible.

Yeast cake layers as secondary membranes in dead-end microfiltration of bovine serum albumin

Dead-end filtration of bovine serum albumin was performed in a phosphate buffer through a yeast cake layer deposited on an asymmetric, polysulfone microfiltration membrane having a nominal pore size of 0.2 μm. Yeast cake layers of varying thicknesses were preformed in two ways - by gravity settling prior to the onset of filtration and by vacuum filtration. The role of the cake layer of rejected cells as a secondary membrane for reducing protein transmission and affecting permeate flux was studied. The steady-state flux was found to be higher in the presence of a thin cake layer than in the absence of a cake layer. This is thought to result from the yeast cake serving as a filter-aid to remove membrane foulants from the protein solution. Due to the micro-channeling effects, higher fluxes were observed for filtration through a cake layer preformed by vacuum filtration, as compared to the corresponding values for a cake layer of equal dry mass preformed by gravity settling. The protein transmission studies revealed three types of fouling - membrane fouling due to the internal pore deposition of protein, protein adsorption through the entire cake depth, and surface filtration leading to protein rejection at the cake surface.

Calcium‐dependent secretory vesicle‐binding and lipid‐binding proteins of Saccharomyces cerevisiase

Yeast (Saccharomyces cerevisiae) cytosol was examined for the presence of calcium-dependent membrane- or lipid-binding proteins that might play fundamental roles in membrane-associated phenomena in stimulated cells. A complex group of proteins was isolated from late log phase cultures of yeast strain YP3 on the basis of calcium-dependent association with yeast secretory vesicles isolated from the temperature-sensitive sec6-4 secretory mutant. The masses of the major proteins in this group were 32, 35, 47, 51, 55, 60 and 120 kDa. A similar group of proteins was isolated by calcium-dependent association with bovine brain lipids enriched in the predominant acidic phospholipids of the yeast secretory vesicles. The 47 kDa protein was highly purified when commercial yeast cake was used as the source of yeast cytosol. The 32 kDa and 60 kDa proteins were demonstrated to reassociate with lipids at calcium concentrations of 100 microM or higher, while no association was promoted by 2 mM-magnesium. The 47 kDa protein could be removed from lipids by reducing the calcium concentration to between 1 and 32 microM. The sequences of peptides isolated from digests of several of these proteins indicate that they are novel proteins but are insufficient to judge the possible homology of these proteins with mammalian membrane-binding proteins. The sequence data may be adequate to permit isolation and modification of the corresponding genes in order to assess the possible function of this class of proteins in stimulated cells.