Fermentation Performance (fermentation + performance)

Distribution by Scientific Domains
Distribution within Life Sciences


Selected Abstracts


Yeast responses to stresses associated with industrial brewery handling

FEMS MICROBIOLOGY REVIEWS, Issue 5 2007
Brian R. Gibson
Abstract During brewery handling, production strains of yeast must respond to fluctuations in dissolved oxygen concentration, pH, osmolarity, ethanol concentration, nutrient supply and temperature. Fermentation performance of brewing yeast strains is dependent on their ability to adapt to these changes, particularly during batch brewery fermentation which involves the recycling (repitching) of a single yeast culture (slurry) over a number of fermentations (generations). Modern practices, such as the use of high-gravity worts and preparation of dried yeast for use as an inoculum, have increased the magnitude of the stresses to which the cell is subjected. The ability of yeast to respond effectively to these conditions is essential not only for beer production but also for maintaining the fermentation fitness of yeast for use in subsequent fermentations. During brewery handling, cells inhabit a complex environment and our understanding of stress responses under such conditions is limited. The advent of techniques capable of determining genomic and proteomic changes within the cell is likely vastly to improve our knowledge of yeast stress responses during industrial brewery handling. [source]


Influence of nutrients on proteinase A activity in draft beer during fermentation

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 6 2010
Xin Hao
Summary With the increase of ,-amino nitrogen concentrations from 90 to 230 mg L,1, proteinase A (PrA) in wort fermentations was showing a downward trend while higher alcohols contents a U-shaped one. The level of 210 mg L,1 of ,-amino nitrogen supplement, at which wort fermentation exhibited a low PrA activity and a level of higher alcohols below the industrial norm (90 mg L,1), was used as the optimised ,-amino nitrogen concentration for further exploring the effect of biotin levels on PrA activity. In the biotin range of 0,65 ,g L,1, PrA activity registered the lowest value when biotin level was at 50 ,g L,1. Medium with 210 mg L,1 of ,-amino nitrogen and 50 ,g L,1 of biotin was therefore adopted for investigating influences of inorganic salt Fe2(SO4)3, KH2PO4, ZnSO4 and MgSO4 on PrA production. It was shown that Fe2(SO4)3 and KH2PO4 had significant influence on PrA production while ZnSO4 and MgSO4 did not. Based on above findings, an optimised set of nutritive elements was determined and used in fermentation. The results indicated that the activity of PrA reduced by 60% without noticeably effects of the fermentation performance and beer flavour. [source]


The role of GAP1 gene in the nitrogen metabolism of Saccharomyces cerevisiae during wine fermentation

JOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2009
R. Chiva
Abstract Aim:, The aim of this study was to analyse the relevance of the general amino acid permease gene (GAP1) of the wine yeast Saccharomyces cerevisiae on nitrogen metabolism and fermentation performance. Methods and Results:, We constructed a gap1 mutant in a wine strain. We compared fermentation rate, biomass production and nitrogen consumption between the gap1 mutant and its parental strain during fermentations with different nitrogen concentrations. The fermentation capacity of the gap1 mutant strain was impaired in the nitrogen-limited and -excessive conditions. The nitrogen consumption rate between the wild strain and the mutant was different for some amino acids, especially those affected by nitrogen catabolite repression (NCR). The deletion of GAP1 gene also modified the gene expression of other permeases. Conclusions:, The Gap1 permease seems to be important during wine fermentations with low and high nitrogen content, not only because of its amino acid transporter role but also because of its function as an amino acid sensor. Significance and Impact of the Study:, A possible biotechnological advantage of a gap1 mutant is its scarce consumption of arginine, whose metabolism has been related to the production of the carcinogenic ethyl carbamate. [source]


Flocculation onset in Saccharomyces cerevisiae: the role of nutrients

JOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2005
S. Sampermans
Abstract Aims:, To examine the role of the nutrients on the onset of flocculation in an ale-brewing strain, Saccharomyces cerevisiae NCYC 1195. Methods and Results:, Flocculation was evaluated using the method of Soares, E.V. and Vroman, A. [Journal of Applied Microbiology (2003) 95, 325]. For cells grown in chemically defined medium (yeast nitrogen base with glucose) or in rich medium (containing yeast extract, peptone and fermentable sugars: fructose or maltose), the onset of flocculation occurred after the end of exponential respiro-fermentative phase of growth being coincident with the attainment of the lower level of carbon source in the culture medium. Cells, in exponential respiro-fermentative phase of growth, transferred to a glucose-containing medium without nitrogen source, developed a flocculent phenotype, while these carbon source starved cells, in the presence of all other nutrients that support growth, did not flocculate. In addition, cells in exponential phase of growth, under catabolite repression, when transferred to a medium containing 0·2% (w/v) of fermentable sugar (fructose or maltose) or 2% (v/v) ethanol, showed a rapid triggering of flocculation, while when incubated in 2% (v/v) glycerol did not develop a flocculent phenotype. Conclusions:, The onset of flocculation occurs when a low sugar and/or nitrogen concentration is reached in culture media. The triggering of flocculation is an energetic dependent process influenced by the carbon source metabolism. The presence of external nitrogen source is not necessary for developing a flocculent phenotype. Significance and Impact of the Study:, This work contributes to the elucidation of the role of nutrients on the onset of flocculation in NewFlo phenotype yeast strains. This information might be useful to the brewing industry, in the control of yeast flocculation, as the time when the onset of flocculation occurs can determine the fermentation performance and the beer quality. [source]


Expression of 2 Lipomyces kononenkoae,-Amylase Genes in Selected Whisky Yeast Strains

JOURNAL OF FOOD SCIENCE, Issue 7 2004
K. la Grange-Nel
ABSTRACT: Nineteen whisky yeasts were evaluated according to their fermentation performance and ability to produce a palatable spirit. Four of these strains were selected and, together with a commercial wine yeast strain (control), were transformed with integration plasmids containing the LKA1 and LKA2 , -amylase genes from the yeast Lipomyces kononenkoae. Fermentation trials with starch-containing media indicated that the transformants produced between 47% and 66% of the theoretical ethanol yield. This study has resulted in progress toward the development of whisky yeast that could ultimately be used in a process during which production of amylases, hydrolysis of starch, and fermentation of resulting sugars to grain whisky occur in a single step. [source]


Effect of overexpression of transcription factors on the fermentation properties of Saccharomyces cerevisiae industrial strains

LETTERS IN APPLIED MICROBIOLOGY, Issue 1 2009
L. Hou
Abstract Aims:, To investigate the effect of modulation of transcription factors on the fermentation properties of Saccharomyces cerevisiae industrial strains and to evaluate whether overexpression and co-overexpression of transcription factors would result in higher ethanol yield. Methods and Results:, A mutant gene spt15 (Phe177Ser, Tyr195His, Lys218Arg) was constructed by polymerase chain reaction mediated site-directed mutagenesis. The fermentation properties of the engineered strains in very high gravity fermentations were investigated. It is found that overexpression of SPT3 can enhance the resistance to ethanol and osmotic stress. On the contrary, overexpression of SPT15 or spt15 cannot obviously improve osmotic and ethanol tolerance of industrial strains. Additionally, simultaneous overexpression of SPT15 and SPT3 can not only distinctly enhance the resistance to ethanol and osmotic stress, but also improve fermentation performance. Conclusions:, Simultaneous modulation of the expression level of SPT15 and SPT3 can increase the production of ethanol by improving osmotic tolerance and ethanol tolerance of industrial strains. Significance and Impact of the Study:, Modulation of transcription factors provides a route to fermentation phenotypes of industrial yeast strains that are not readily accessible by traditional methods. [source]


Protective agents used to reverse the metabolic changes induced in wine yeasts by concomitant osmotic and thermal stress

LETTERS IN APPLIED MICROBIOLOGY, Issue 2 2002
A. Caridi
Aims:,The reversion of the metabolic changes induced in wine yeasts by stressors. Methods:,Six strains of Saccharomyces were inoculated in grape must containing over 400 g l,1 of sugar and incubated at 35 °C, both with and without the addition of 100 mg l,1 of catechin, inositol or SO2. Results:,Significant correlations between addition of the stress-protectants and change in the metabolic behaviour of the wine yeasts were observed. Depending on strain and protectant, and expressing data as a percentage of increase or decrease compared to the control, fermentation vigour after 3 d increased by up to 10%, titratable acidity of the wines increased by up to 7%, ethanol content increased by up to 20%, unitary acetic acid production decreased by up to 35%, and unitary glycerol production decreased by up to 20%. Impact of Study:,By using protective agents it is possible to minimize the abnormal fermentation performance that wine yeasts exhibit under thermal and osmotic stress. [source]


The impact of media composition and petite mutation on the longevity of a polyploid brewing yeast strain

LETTERS IN APPLIED MICROBIOLOGY, Issue 1 2000
C.D. Powell
Ageing in Saccharomyces cerevisiae is a finite phenomenon, determined by replicative, rather than chronological lifespan. Yeast physiological condition is known to influence industrial fermentation performance, however, until recently cellular senescence has not been considered as a brewing yeast stress factor. A polyploid lager yeast (BB11) and a brewery isolate, exhibiting petite mutation were analysed for longevity. It was observed that mitochondrial deficiency induced a reduction in lifespan. In addition, replicative capacity was perceived to be dependent on environmental conditions. [source]


Parameter oscillation attenuation and mechanism exploration for continuous VHG ethanol fermentation

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009
F.W. Bai
Abstract A bioreactor system composed of a stirred tank and three tubular bioreactors in series was established, and continuous ethanol fermentation was carried out using a general Saccharomyces cerevisiae strain and a very high gravity medium containing 280 g,L,1 glucose, supplemented with 5 g,L,1 yeast extract and 3 g,L,1 peptone. Sustainable oscillations of glucose, ethanol, and biomass were observed when the tank was operated at the dilution rate of 0.027 h,1, which significantly affected ethanol fermentation performance of the system. After the tubular bioreactors were packed with 1/2, Intalox ceramic saddles, the oscillations were attenuated and quasi-steady states were achieved. Residence time distributions were studied for the packed bioreactors by the step input response technique using xylose as a tracer, which was added into the medium at a concentration of 20 g,L,1, indicating that the backmixing alleviation assumed for the packed tubular bioreactors could not be established, and its contribution to the oscillation attenuation could not be verified. Furthermore, the role of the packing's yeast cell immobilization in the oscillation attenuation was investigated by packing the tubular bioreactors with packings with significant difference in yeast cell immobilization effects, and the experimental results revealed that only the Intalox ceramic saddles and wood chips with moderate yeast cell immobilization effects could attenuate the oscillations, and correspondingly, improved the ethanol fermentation performance of the system, while the porous polyurethane particles with good yeast cell immobilization effect could not. And the viability analysis for the immobilized yeast cells illustrated that the extremely lower yeast cell viability within the tubular bioreactors packed with the porous polyurethane particles could be the reason for their inefficiency, while the yeast cells loosely immobilized onto the surfaces of the Intalox ceramic saddles and wood chips could be renewed during the fermentation, guaranteeing their viability and making them more efficient in attenuating the oscillations. The packing Raschig rings without yeast cell immobilization effect did not affect the oscillatory behavior of the tubular bioreactors, further supporting the role of the yeast cell immobilization in the oscillation attenuation. Biotechnol. Bioeng. 2009;102: 113,121. © 2008 Wiley Periodicals, Inc. [source]


Comparison of glucose/xylose cofermentation of poplar hydrolysates processed by different pretreatment technologies

BIOTECHNOLOGY PROGRESS, Issue 2 2009
Yulin Lu
Abstract The inhibitory effects of furfural and acetic acid on the fermentation of xylose and glucose to ethanol in YEPDX medium by a recombinant Saccharomyces cerevisiae strain (LNH-ST 424A) were investigated. Initial furfural concentrations below 5 g/L caused negligible inhibition to glucose and xylose consumption rates in batch fermentations with high inoculum (4.5,6.0 g/L). At higher initial furfural concentrations (10,15 g/L) the inhibition became significant with xylose consumption rates especially affected. Interactive inhibition between acetic acid and pH were observed and quantified, and the results suggested the importance of conditioning the pH of hydrolysates for optimal fermentation performance. Poplar biomass pretreated by various CAFI processes (dilute acid, AFEX, ARP, SO2 -catalyzed steam explosion, and controlled-pH) under respective optimal conditions was enzymatically hydrolyzed, and the mixed sugar streams in the hydrolysates were fermented. The 5-hydroxymethyl furfural (HMF) and furfural concentrations were low in all hydrolysates and did not pose negative effects on fermentation. Maximum ethanol productivity showed that 0,6.2 g/L initial acetic acid does not substantially affect the ethanol fermentation with proper pH adjustment, confirming the results from rich media fermentations with reagent grade sugars. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]