Crossflow filtration of yeast broth cultivated in molasses

A broth of yeast cells cultivated in molasses was crossfiltered with a thin-channel module. The permeation flux gradually decreased at a constant cell concentration. The flux was much lower than that obtained for yeast broth cultivated in yeast extract, polypeptone, and dextrose (YPD) medium during the filtration. The flux did not depend on the membrane pore size (0.45 to 5 mum). The steady-state flux was one-twentieth that calculated for a cake filtration mode from the amount of cake per unit filtration area and the specific resistance of the cake measured in a dead-end filtration apparatus. The lower flux was due to small particles (most of which were less than 1 mum in diameter) in the molasses. The mehanism of crossflow filtration of broths of yeast cells cultivated in molasses was clarified by analysis of the change in flux with time and observations with scanning electron microscopy. At the initial stage of crossflow filtration the yeast cells and particles from the molasses were deposited on the membrane to form the molasses were deposited on the membrane to form a cake in a similar way to dead-end filtration. After the deposition of cells onto the membrane ceased, the fine particles from molasses formed a thin layer, which had higher resistance than the cake formed next to the membrane. The backwashing method was effective to increase the flux. The flux increased low when the pore size was 0.45 to 0.08 mum, but using larger pores of 3 to 5 mum it returned almost to the bases line. (c) 1994 John Wiley & Sons, Inc.     

Microfiltration of recombinant yeast cells using a rotating disk dynamic filtration system

To develop a highly efficient cell harvest step under time constraint, a novel rotating disk dynamic filtration system was studied on the laboratory scale (0.147-ft.(2) nylon membrane) for concentrating recombinant yeast cells containing an intracellular product. The existing cross-flow microfiltration method yielded pseudo-steady state flux values below 25 LMH (L/m(2). h) even at low membrane loadings (10 L/ft.(2)). By creating high shear rates (up to 120,000(-1)) on the membrane surface using a rotating solid disk, this dynamic filter has demonstrated dramatically improved performance, presumably due to minimal cake buildup and reduced membrane fouling. Among the many factors investigated, disk rotating speed, which determines shear rates and flow patterns, was found to be the most important adjustable parameter. Our experimental results have shown that the flux increases with disk rotating speed, increases with transmembrane pressure at higher cell concentrations, and can be sustained at high levels under constant flux mode. At a certain membrane loading level, there was a critical speed below which it behaved similarly to a flat sheet system with equivalent shear. Average flux greater than 200 LMH has been demonstrated at 37-L/ft.(2) loading at maximum speed to complete sixfold concentration and 15-volume diafiltration for less than 100 min. An order of magnitude improvement over the crossflow microfiltration control was projected for large scale production. This superior performance, however, would be achieved at the expense of additional power input and heat dissipation, especially when cell concentration reaches above 80 g dry cell weight (DCW)/L. Although a positive linear relationship between power input and dynamic flux at a certain concentration factor has been established, high cell density associated with high viscosity impacted adversely on effective average shear rates and, eventually, severe membrane fouling, rather than cake formation, would limit the performance of this novel system. (c) 1995 John Wiley & Sons, Inc.     

Crossflow filtration of baker's yeast with periodical stopping of permeation flow and bubbling

The periodical stopping of permeation flow was applied to increase the permeation flux in crossflow filtration of commercially available baker's yeast cell suspension. The permeation flux after 3 h filtration in the crossflow filtration increased to 8 x 10(-5) m(3) /m(2) s (290 L/m(2) h) from 2 x 10(-5) m(3)/m(2) s (72 L/m(2) h) by applying the periodical stopping of permeation. Introduction of air bubbles during the stopping period of permeation further increased the flux.(c) John Wiley & Sons, Inc.     

Real-time fuzzy-knowledge-based control of Baker's yeast production

A real-time fuzzy-knowledge-based system for fault diagnosis and control of bioprocesses was constructed using the object-oriented programming environment Small-talk/V Mac. The basic system was implemented in a Macintosh Quadra 900 computer and built to function connected on line to the process computer. Fuzzy logic was employed in handling uncertainties both in the knowledge and in measurements. The fuzzy sets defined for the process variables could be changed on-line according to process dynamics. Process knowledge was implemented in a graphical two-level hierachical knowledge base. In on-line process control the system first recognizes the current process phase on the basis of top-level rules in the knowledge-base. Then, according to the results of process diagnosis based on measurement data, the appropriate control strategy is subsequently inferred making use of the lower level rules describing the process during the phase in question. (c) 1995 John Wiley & Sons, Inc.     

Reductive biotransformations of organic compounds by saccharomyces cerevisiae: study of oxidoreductases involved using electrophoretic zymograms

The role of oxidoreductases in reduction of carbonyl compounds was investigated by application of zymogram techniques. Eight bands were observed using ethanol with nicotinamide adenine dinucleotide (NAD) as coenzyme. Bands observed with lactic acid and (R)-(-)-phenyl-1,2-ethanediol with nicotinamide adenine dinucleotide phosphate (NADP) had similar R(m) values. 2-Hydroxyvalerate and malate manifested bands having similar R(m) values and were active with both NAD and NADP. Based on their structural similarity and identical R(m) values, oxidation of 1,4-cyclooctanediol (band #2) and cis-1,5-cyclooctanediol may be due to a common enzyme. The PAGE-zymogram technique may be used on a preparative scale to facilitate purification and full characterization on the observed stained bands.     

Gas phase biotransformation reaction catalyzed by baker's yeast

The gas phase continuous production of acetaldehyde from ethanol and hexanol from hexanal using dried baker's yeast was studied as an alternative approach to conventional processes. The effects of water activity, activity of substrates, and amount of yeast on the performance of the continuous bioreactor were investigated. The extent of yeast hydration and ethanol activity are the most important factors affecting yeast activity and stability.     

Reduction of α-Azidopropiophenone by Immobilized Baker's Yeast

Baker's yeast immobilized on montmorillonite K10 and chrysotile reduced α-azidopropiophenone to the corresponding azidoalcohols syn and anti with good chemical yield and enantiomeric excess.     

Cadmium biosorption by Saccharomyces cerevisiae

Cadmium uptake by nonliving and resting cells of Saccharomyces cerevisiae obtained from aerobic or anaerobic cultures from pure cadmium-bearing solutions was examined. The highest cadmium uptake exceeding 70 mg Cd/g was observed with aerobic baker's yeast biomass from the exponential growth phase. Nearly linear sorption isotherms featured by higher sorbing resting cells together with metal deposits localized exclusively in vacuoles indicate the possibility of a different metal-sequestering mechanism when compared to dry nonliving yeasts which did not usually accumulate more than 20 mg Cd/g. The uptake of cadmium was relatively fast, 75% of the sorption completed in less than 5 min. (c) 1993 Wiley & Sons, Inc.     

A Multivariate Re-Examination of Experimental Condition Effects on Acyloin-Type Condensation Mediated by Saccharomyces Cerevisiae

Statistical methods of optimization were applied to the stereoselective synthesis of (2S,3R)-5-phenylpent-4-en-2,3-diol mediated by baker's yeast. The quantitative effects of seven variables, i.e. pH, temperature, concentration of cinnamaldehyde, yeast and glucose, addition of pyruvate and acetaldehyde were investigated using a fractional factorial design. This approach gave informations about the chemical behaviour of the yeast. Response surface methodology was employed to describe the variability of the yield in the experimental domain.     

Design and evaluation of control strategies for high cell density fermentations

A methodology for the design and evalution of bioprocess control strategies is presented. The strategies manage nutrient supply with demand and vary with the metabolic condition and phase of fermentation operation. Six carbon source addition strategies are based on different combinations of available measurements; they are described and evaluated under different operating conditions for yeast cultivation. It is concluded that a single control strategy is not the most appropriate under all possible operating conditions. An oxygen uptake rate-based control strategy performs better with a mean respiratory quotient (RQ) value less than 1.1 during an oxygen limitation than an ethanol control strategy which had a mean RQ of 14. The designed strategies and an approach of applying the strategy that best matches fermentation conditions consistently enables achievement of high cell densities 78.7 g DCW/L and yields 0.50 g DCW/g glucose as the mean values for three fermentations.     

Phytase-active yeasts from grain-based food and beer

Aims: To screen yeast strains isolated from grain‐based food and beer for phytase activity to identify high phytase‐active strains. Methods and Results: The screening of phytase‐positive strains was carried out at conditions optimal for leavening of bread dough (pH 5·5 and 30°C), in order to identify strains that could be used for the baking industry. Two growth‐based tests were used for the initial testing of phytase‐active strains. Tested strains belonged to six species: Saccharomyces cerevisiae, Saccharomyces pastorianus, Saccharomyces bayanus, Kazachstania exigua (former name Saccharomyces exiguus), Candida krusei (teleomorph Issachenkia orientalis) and Arxula adeninivorans. On the basis of initial testing results, 14 strains were selected for the further determination of extracellular and intracellular (cytoplasmic and/or cell‐wall bound) phytase activities. The most prominent strains for extracellular phytase production were found to be S. pastorianus KVL008 (a lager beer strain), followed by S. cerevisiae KVL015 (an ale beer strain) and C. krusei P2 (isolated from sorghum beer). Intracellular phytase activities were relatively low in all tested strains. Conclusions: Herein, for the first time, beer‐related strains of S. pastorianus and S. cerevisiae are reported as phytase‐positive strains. Significance and Impact of the Study: The high level of extracellular phytase activity by the strains mentioned previously suggests them to be strains for the production of wholemeal bread with high content of bioavailable minerals.     

The use of hollow fiber cross-flow microfiltration in bioaccumulation and continuous removal of heavy metals from solution by Saccharomyces cerevisiae

Cross-flow microfiltration was shown to retain Saccharomyces cerevisiae biomass utilized for heavy metal bioaccumulation. The passage of metal-laden influent through a series of sequential bioaccumulation systems allowed for further reductions in the levels of copper, cadmium, and cobalt in the final effluent than that afforded by a single bioaccumulation process. Serial bioaccumulation systems also allowed for partial separation of metals from dual metal influents. More than one elemental metal cation could be accumulated simultaneously and in greater quantities than when a single metal was present in the effluent (Cu(2+) 0.43 mmol, Cu(2+) + Cd(2+) 0.67 mmol, and Cu(2+) + Co(2+) 0.83 mmol/g yeast dry mass when the initial concentration of each of the metal species was 0.2 mmol.L(-1)). Co-accumulation of two different metal cations allowed higher total levels of bioaccumulation than found with a single metal. The flux rate was 2.9 x 10(2) L.h(-2)mum(-2) using a polypropylene microfiltration membrane (0.1 mum pore size) at 25 degrees C. (c) 1994 John Wiley & Sons, Inc.     

Stereoselective bioreduction of 1-(5-phenylfuran-2-yl)-ethanones mediated by baker's yeast

Abstract

Baker's yeast mediated reduction of various phenylfuran-2-yl-ethanones has been studied. The influence of the reaction conditions, the type and position of the substituents, as well the presence of various additives on the enantiomeric composition of the products and the reaction yield are discussed. The absolute configuration of the reaction products was established using a retrosynthetic procedure.     

A molecular genetic study of natural strains of Saccharomyces isolated from Asturian cider fermentations

AIMS: To analyse the genetic diversity and the dynamics of Saccharomyces strains in spontaneous fermentation in ciders. The effect of the cellar, harvest and cider-making technology were evaluated. METHODS AND RESULTS: The ecology of spontaneous cider fermentations in the same cellar (Asturias) was studied for two consecutive harvests (2000 and 2001) by using mtDNA restriction analysis. Our results showed that there was a succession of genetically different strains of Saccharomyces during cider production. In general, strains of Saccharomyces bayanus species predominated at the early fermentation steps (begining and/or tumultuous fermentations), while Saccharomyces cerevisiae yeasts were the most abundant at the end of the fermentation. Five S. bayanus strains (patterns III, VII, VIII, XV and XVII) were present at significant frequencies in all the experimental tanks during the two consecutive years. The results of the cluster analysis (unweighted pair group method using average linkage) showed higher similarities for the patterns III, XV, VII and VIII. Therefore, these strains should be considered associated with the microbiota of this cellar. CONCLUSIONS: A high polymorphism within populations of Saccharomyces was found throughout the different stages of Asturian production of cider. In all the cider fermentations, a variable number of S. bayanus and S. cerevisiae strains was always present. Our results indicate, over the period of time studied, the existence of the natural microbiota in the cellar. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has allowed us to gain a better understanding of the role of wild Saccharomyces yeast in Asturian cider fermentations.     

Presence of non-suppressive, M2-related dsRNAs molecules in Saccharomyces cerevisiae strains isolated from spontaneous fermentations

Total dsRNA extractions in five killer K2 strains of Saccharomyces cerevisiae isolated from spontaneous fermentations revealed the presence of a novel dsRNA fragment (which we named NS dsRNA) of approximately 1.30 kb, together with L and M2 dsRNAs. NS dsRNA appeared to be encapsidated in the same kind of viral particles as L and M2 dsRNA. Northern blot hybridization experiments indicated that NS dsRNA was derived from M2 dsRNA, likely by deletion of the internal A+U-rich region. However, unlike S dsRNAs (suppressive forms derived from M1 dsRNA in K1 killers), NS dsRNA did not induce exclusion of the parental M2 dsRNA when the host strain was maintained for up to 180 generations of growth.