Pure Yeast Cultures Research Articles

Industrial‐scale microvinification with autochthonous yeasts, selected in the Denominación de Origen Ycoden‐Daute‐Isora (part 1)

In this project we conducted industrial‐scale research in a wine cellar, where autocthonous yeasts selected from the Denominación de Origen Ycoden‐Daute‐Isora were inoculated. Their behaviour was initially analysed on a minor scale in an experimental wine cellar. The vindication was carried out using the variety “White Listan”, adding pure culture of yeast belonging to the species Saccharomyces cercvisiae, Debaryomyces hansenii and Torulaspora delbrueckii, and observing its influence in the initial flora of the must. In so doing, we attempted to ensure that the selection and valuation of this yeast are in accordance with the features of the wine in this “appellation d'origine”.

Attraction of a flying nitidulid (Carpophilus humeralis) to volatiles produced by yeasts grown on sweet corn and a corn-based medium.

Attraction to microbial volatiles was examined for the sap beetle, Carpophilus humeralis, which is a pest of maize. Using 54 pure yeast and bacterial cultures, we evaluated differences in volatile emissions among species of microorganisms and whether these differences were associated with insect attraction. On a sterile corn-based medium, both yeasts and bacteria generally multiplied well and produced detectable volatile metabolites. The yeasts ranged from inactive to highly attractive, but no bacterial cultures attracted beetles above control levels. A variety of alcohols, esters, ketones, acids, and phenolic compounds were identified from the headspace above yeast cultures. Growth, volatile production, and, ultimately, attractiveness to beetles depend strongly on the ability of the yeasts to assimilate and/or ferment the carbohydrates present. Abundant volatile production on sweet corn was observed only with yeasts that are able to ferment sucrose and/or maltrose. Saccharomyces cerevisiae (ferments glucose, sucrose, and maltose) and Candida shehatae (ferments glucose and maltose) produced considerably more attractive volatiles than Candida guilliermondii, which only ferments glucose. Yeast volatiles important for beetle attraction included typical fermentation-associated substances (ethanol, acetaldehyde, 2-methyl-1-propanol, 1-propanol, ethyl acetate, 3-methyl-1-butanol and 2-methyl-1-butanol), and also 3-hydroxy-2-butanone, whose presence was not correlated with the occurrence of fermentation. Using aqueous mixtures of synthetic components that produced headspace compositions simulating those of attractive yeasts, it was shown that the typical fermentation volatiles are attractive but not essential for attractiveness. 3-Hydroxyl-2-butanone is sufficient but not necessary, although its attractiveness is enhanced by the presence of fermentation volatiles such as ethanol and 2-methyl-1-proponol. In nature, the beetles could take advantage of a variety of different microbial metabolic processes to locate hosts. The laboratory bioaasays in this study involved flight and therefore were particularly relevant to host-finding behavior in the field.

Optimisation of methodology for enumeration of xerophilic yeasts from foods

Xerophilic yeasts grow in intermediate moisture foods ( a w, 0.65–0.85) such as sugar syrups, fruit concentrates, jams and brines. Non-osmophilic yeasts are enumerated by diluting in 0.1% peptone and then plated onto media such as malt extract or glucose yeast extract agar. In the presence of moulds the yeasts are enumerated in dichloran rose bengal chloramphenicol agar (DRBC). These procedures were demonstrated to be unsatisfactory for the enumeration of xerophilic yeasts in low a w foods. Investigations using pure cultures of xerophilic yeasts as well as naturally contaminated apple juice concentrates and glacé cherries have shown that a reduced a w diluent, in particular 30% w/w glycerol in combination with tryptone 10% glucose yeast extract agar (TGY) optimises the recovery of the yeasts, especially sublethally injured cells. The inclusion of sodium chloride in either the diluents or the culture media was not necessary to optimise the recovery of D. hansenii growing in 20% sodium chloride broths.

Pure yeast culture fermentation of cocoa (Theobroma cacao L): effect on yield of sweatings and cocoa bean quality

Cocoa sweatings, the pale yellowish liquid that drains off during cocoa fermentation, is the breakdown product of the mucilage surrounding the fresh cocoa bean, and constitutes about 10% of the weight of the cocoa fruit. On average, about 1.9 million l of sweatings are produced annually in Ghana during the cocoa harvesting season. It has been shown to be a suitable medium for the production of wines, alcohol, marmalade, jam and syrup. Its rapid collection in high yields and quality is the first step to its utilization on a commercial scale. Thus pure yeast culture fermentation of cocoa under controlled temperature conditions and its effect on yield of sweatings and final cocoa bean quality was investigated. Cocoa fermentations employing Saccharomyces chevalieri or Kluyveromyces fragilis alone gave significantly higher yields of sweatings (p 0.05) than controls. The initial rates of sweating by the two strains were also very high but dropped to a constant minimum value after 12h of fermentation. In contrast, fermentations employing Torulopsis candida or Candida norvengensis alone as well as different combinations of all the yeast strains did not give any significant difference in yield compared to controls (p 0.05). Fermentations using S. chevalieri alone or other combinations in which S. chevalieri was present gave beans with acceptable quality based on different quality indices used for grading cocoa beans commercially.

Review: Biochemical and technological assessment of the metabolism of pure and mixed cultures of yeast and lactic acid bacteria in breadmaking applications / Revisión: Aspectos bioquímicos y tecnológicos del metabolismo de cultivos puros y mixtos de levaduras y bacterias ácido lácticas en panificación

The production of varieties of breads with the quality required at present by the European consumer closely relates to the proper use of starting microorganisms in controlled and optimized breadmaking conditions. The relationship between processing requirements and wheat bread quality involves an understanding of the metabolism of the starting microflora which regulate production or assimilation of suitable and unsuitable metabolites during the breadmaking process, mediated by the specific enzyme activities and nutritional requirements of yeast and lactic acid bacteria. In this paper, recent advances in the biochemical and technological assessment of pure and mixed cultures of yeast and lactic acid bacteria in breadmaking applications are reviewed. Metabolite profiles in model and simplified wheat flour systems, performance of breadmaking starters in straight and sourdough systems, and relationships between process conditions, tech nological performance and metabolism of fermentation starters are discussed.

Aroma Compounds in Wine as Influenced by Apiculate Yeasts

ABSTRACTAroma compounds of wines resulting from fermentation of sterile grape musts from Monastrell variety inoculated with pure and mixed cultures of apiculate and Saccharomyces yeasts, were isolated and analyzed by gas chromatography with flame ionization and mass spectrometry. Samples fermented with mixed cultures produced a higher concentration of selected compounds and higher total amounts of alcohols and acids, in contrast with wines produced with pure cultures of Saccharomyces spp. Apiculate yeasts are important in the chemical composition and quality of wine.

Two-Day Yeast and Mold Enumeration Using the ISO-GRID® Membrane Filtration System in Conjunction with YM-11 Agar

A 2-day yeast and mold enumeration procedure using the ISO-GRID® membrane filtration system in conjunction with a new culture medium, YM-11 agar, was compared to the conventional 5-day pour plate method using antibiotic-supplemented potato dextrose agar. Performance of the new method was evaluated using both pure cultures of yeasts and molds and 275 food samples, representing 25 different food products. The 2-day ISO-GRID® method yielded counts equivalent to or significantly higher than the 5-day pour plate method in 23 of the 25 food product categories.

A biotechnological valorization and treatment of olive mill waste waters by selected yeast strains

Olive mill waste waters were diluted to 1/10, supplied with 2% urea and inoculated with yeast strains. 20 yeast strains isolated from Olive Mill Waste (OMW) water were screened for their biomass production, GOD reduction and polyphenols bioconversion activities. Pure cultures of yeasts were realized in 100 ml erlen-meyer flasks. 50 ml cultures were used and the flasks were incubated at room temperature (22°G) on a shaker. Biomass production, COD (chemical oxygen demand) reduction and Polyphenols bioconversion were followed up in the inoculated OMW waters. Results showed that the urea supply improve significantly the biomass production relatively to the control. This reached in some assays 2.06% expressed as g of biomass dry weight per 100 mL of OMW water. Polyphenols removal was estimated to around 50% and the COD was decreased from 54.14 g/Kg to 21.56 g/Kg. This aerobic treatment lead to the biomass production and also to a pretreated efluent by the COD and the removal of the methanization inhibiting polyphenolic compounds.

Amino Acid Metabolism by Yeasts and Lactic Acid Bacteria during Bread Dough Fermentation

ABSTRACTMetabolism of 22 free amino acids (AA) during fermentation(early and later steps) of wheat dough samples started with pure and associated cultures of yeast and lactic acid bacteria, and commercial compressed yeast (CY) were investigated. Unfermented and fermented straight doughs were studied byReversed‐Phase HPLC of their dansyl derivatives. Used as starters were strains of Saccharomyces cervisiae, Lactobacillus brevis, Lactobacillus plantarum and Enterococcus faecium. Statistical data analysis indicated clustering of samples with yeast and samples without yeast (including uninoculated doughs) respectively, based on rate of metabolism of acidiC., basiC., aliphatic and aromatic A A. Differences in AA metabolism during the later fermentation step (DF2) categorized bacterial starters into groups according to balance between degree of assimilation(D F2<0) and exoproteolytic release(DF2>0) of amino acids.

Contribution of the microbial mass to the nitrogen profile of wheat bread doughs started with pure and mixed cultures of yeast and lactic acid bacteria

This paper describes work investigating the contribution of low-molecular-mass nitrogen metabolites (free amino acids and peptides) to the microbial mass of pure strains of fermentation microorganisms (Saccharomyces cerevisiae, P38;Lactobacillus brevis, B33;L. plantarum, B23 andEnterococcus faecium, B12) when they are incorporated as starters individually and in mixed cultures to wheat bread doughs. Under the experimental conditions used, the microbial mass of P38 releases mainly γ-aminobutyric acid, proline, valine, lysine, isoleucine, glycine and alanine, which account together for less than 5% of the amino acid content of the corresponding bread dough; amino acids in the microbial mass of lactic acid bacteria, mainly glycine and alanine, amount to 1–2% of the dough. The peptide contribution of microbial mass to bread dough is higher and dependent on the strain. Mixing ingredients induces an increase of 65% in the total amino acid content of dough started with P38, particularly of glutamic acid, glutamine, isoleucine, ornithine, lysine, histidine and tyrosine, and a significant rise in peptide levels of all individual doughs with respect to the values obtained for mixtures of flour, water and salt. Starting bread dough with mixtures of yeast and lactic acid does not increase low-molecular-mass nitrogen levels, the amount of peptides being similar to those of dough containing yeast P38 alone. Addition of B33 induces a remarkable increase in the amino acid content of bread dough, mainly of dicarboxylic acids and their amides, and proline, similar to the composition of free amino acids of dough starter with B33.

Analytical differentiation of wine fermentations using pure and mixed yeast cultures

Thirty-three fermentations of Pedro Ximenez grapes, collected in three degrees of ripeness, were carried out by inoculation with three types of inoculum: pure cultures ofSaccharomyces cerevisiae races and ofTorulaspora delbrueckii, indigenous yeasts, and mixed cultures of indigenous yeasts enriched with the pure cultures. By means of variance analysis 21 compounds were determined whose final concentrations in the wines significantly depended on the musts, the inocula or both. Eleven products that depended significantly on the inocula were subjected to a discriminant analysis in which most of the pure cultures gathered in a discriminant space area different from that occupied by the indigenous yeasts. The centroids corresponding to most of the mixed cultures were shifted to the central area of the discriminant space, moved away from their corresponding pure cultures and approached the indigenous yeasts. The results show a high similarity between the fermentations carried out with mixed cultures with the addedS. cerevisiae races and those fermentations carried out with the indigenous yeasts, with regard to those compounds which were significantly dependent on the inocula.

SPIRAL SYSTEM AND LASER COLONY SCANNER FOR ENUMERATION OF MICROORGANISMS

ABSTRACT Aerobic Plate Count (APC) and spiral plate (Spiral) methods using both manual counting (MC) and laser counting (LC) procedures were compared for pure bacterial, yeast, and mold cultures and raw milk samples. All four combinations of methods (APC‐MC, APC‐LC, Spiral‐MC, and Spiral‐LC) gave similar log10 counts of studied pure microbial cultures, producing results that were not different for the purposes of practical microbiology. With bacterial and yeast cultures, counts differed by less than half a logarithmic cycle (the range of difference = ‐0.26 to +0.42), the range of difference being ‐0.03 to +0.62 for Aspergillus flavus and Penicillium camemberti molds. An exception was noticed with Rhizopus oligosporus mold when plates were read by laser due to large (10–15 mm) colony size. The difference between the readings made manually and by laser colony scanner was about one logarithmic cycle with both APC and Spiral methods. Statistical analyses of the manually read results of bacterial and Saccharomyces cerevisiae spiral plates showed no differences at the 0.05 level of significance between the readings made by four or five persons. For raw milk samples, Spiral‐MC and Spiral‐LC methods gave higher microbial numbers than APC‐MC (63% of samples) and APC‐LC (54% of samples) at 0.05 level of significance (p<0.001). Of the LC results, 75% were within a ± 0.5 logarithmic cycle range when compared to MC results, of which 98% were within the same range. All results were still within a ± 1.0 logarithmic range. When APC and Spiral for raw milk samples were analyzed, LC gave higher microbial numbers compared to MC: 71% of the APC‐LC results were higher than APC‐MC results, and 85% of Spiral‐LC results were higher than Spiral‐MC results at 0.05 level of significance (p<0.001). 77% of the results by either plating technique were within a ± 0.5 logarithmic range.

Effect of germination and fermentation on available carhohydrate content of pearl millet

Germination significantly increased the total soluble sugars, reducing and non-reducing sugar contents of pearl millet with a parallel decrease in its starch content. Fermentation of the sprouts with pure cultures of yeasts ( Saccharomyces cerevisiae or Saccharomyces diastaticus) and lactobacilli ( Lactobacillus brevis or Lactobacillus fermentum) further reduced its starch content. Among the various fermentation combinations studied, sprouts fermented with S. diastaticus and L. brevis combinations had the lowest amounts of starch and the maximum amounts of total soluble and reducing sugars. Other combinations for fermentation of the sprouts also had higher concentrations of total soluble, reducing and non-reducing sugars than those of the unprocessed pearl millet but less when compared with the sprouts alone, perhaps due to utilisation of sugars by the fermenting microflora.

Effect of fermentation by pure cultures of yeasts and lactobacilli on the available carbohydrate content of pearl millet

Single as well as mixed culture fermentations of pearl millet with yeasts ( Saccharomyces cerevisiae or Saccharomyces diastaticus) and lactobacilli ( Lactobacillus brevis or Lactobacillus fermentum) significantly increased the total soluble sugars, reducing and non-reducing sugar content, with a simultaneous decrease in the starch content, of pearl millet flour. S. diastaticus and/or its combination with the lactobacilli hydrolysed the starch content to the maximum and, therefore, resulted in higher concentrations of total soluble, reducing and non-reducing sugars when compared to those of unfermented millet flour.

Effect of Fermentation by Pure Cultures of Yeasts and Lactobacilli on Phytic Acid and Polyphenol Content of Pearl Millet

ABSTRACTSingle and mixed pure culture fermentations of pearl millet flour with yeasts and lactobacilli, namely, Saccharomyces diastaticus, Saccharomyces cerevisiae, Lactobacillus brevis and Lactobacillus fermentum, at 30oC for 72 hr brought about a significant reduction in phytic acid and polyphenols which were present in considerable amounts in pearl millet flour. Reduction in phytic acid was more pronounced than that in the polyphenols.

Immune responses to yeast and mycelial forms of Candida albicans in intraperitoneally infected mice.

Candida albicans E-139 produced pure mycelial and yeast cultures in a low sulphate medium at different temperatures. The influence of the morphological phase, dose and viability of the fungi on the kinetic of delayed-type hypersensitivity (DTH) and anti-mycelial and anti-yeast antibodies have been studied in mice injected intraperitoneally. The mycelial form elicited higher DTH levels than the yeast phase. This effect seems to be related to its antigenic properties. The effect of dose on the immune response depends on the viability of the fungus. The mycelial cytoplasmic antigens were more effective than the yeast ones in detecting antibodies induced during the experiments, particularly during the later stages of the observation periods, suggesting that such antigens may be useful in the serodiagnosis of Candida infections.

Cellular and humoral immune responses to Candida albicans in subcutaneously infected mice.

Pure mycelial and yeast cultures of Candida albicans were produced in a low sulphate medium. Groups of mice were injected subcutaneously with increasing doses of viable or heat-killed mycelial or yeast cells and the kinetics of delayed-type hypersensitivity (DTH), anti-mycelial and anti-yeast antibodies were studied. Both the dose and the morphological phase of C. albicans showed an influence on the development of the DTH, but the viability is the factor which showed the highest influence on this reaction, since on the one hand mice infected with viable yeast or mycelial cells developed higher DTH levels than mice injected with heat killed cells, and on the other hand this factor seems to play an important role in the kinetics of DTH response. The enzyme-linked immunosorbent assay has been adapted to detect antibodies to yeast and mycelial phase cytoplasmic antigens of C. albicans. In contrast with the DTH reactions, neither dose, morphological phase nor viability played an important role on the antibody titer developed. However, the use of mycelial cytoplasmic antigens seems to be better than the yeasts to detect anti-Candida antibodies over the last days studied.

Effect of sodium metabisulphide on ethanol production in coconut inflorescence sap

The addition of up to 200 mg l −1 of sodium metabisulphite to coconut inflorescence sap was found to suppress the non-ethanol producing micro-organisms and permit ethanol production by pure yeast cultures to different extents. At metabisulphite concentrations higher than 150 mg l −1 the ethanol yields from sap fermented with a natural inoculum increased under laboratory conditions. In the field, introduction of sodium metabisulphite to sap collecting pots gave maximum ethanol yield at a concentration of 188 mg l −1 and on fermenting for 36 days. A response function was derived, based on field observations, to predict the ethanol yields at different sodium metabisulphite concentrations up to 325 mg l −1 and durations of fermentation 1 to 5 days.

Sanitization of dentures by several denture hygiene methods

Denture sanitization is an important element in the treatment of denture stomatitis and should be emphasized in instructions to patients. A two-part study was designed to compare the efficacy of eight denture-cleaning methods in removing and/or killing aerobes, anaerobes, and yeasts on dentures. Part I tested the effectiveness of the cleaners on a pure yeast culture of C. albicans. Part II tested the various denture sanitization techniques under actual clinical conditions. The following conclusions were made from the information obtained in this study: Miller's and Kleenite were the most effective sanitizing agents. Brushing the denture with soap and water and soaking the denture in the cleaner Mersene were effective to a lesser degree. Although Clorox and Calgon was effective at killing yeast under in vitro conditions, it was not effective under clinical conditions. The other denture cleaners were not found to be effective under the clinical conditions of this study for the removal and/or killing of any of the three microorganism groups cultured. In the past, the function of denture cleaners has been to remove deposits and stains from dentures. With the present knowledge of the role of microorganisms in the etiology of denture stomatitis, more emphasis should be placed on the ability of denture cleaners to sanitize dentures.

MYGP + COPPER, A MEDIUM THAT DETECTS BOTH SACCHAROMYCES AND NON-SACCHAROMYCES WILD YEAST IN THE PRESENCE OF CULTURE YEAST*

Lin's copper sulphate medium for the detection of non-Saccharomyces wild yeast was modified, mainly by reducing the concentration of copper sulphate, with the aim of producing a medium that could detect a wide range of both non-Saccharomyces and Saccharomyces wild yeast. The performance of the resultant MYGP + Cu medium was compared to that of crystal violet and lysine media using pure cultures of wild yeast, pitching yeast and brewery samples. The growth of the pitching yeasts examined was suppressed more in MYGP + Cu than in crystal violet and the 4 ale yeasts were more susceptible to copper inhibition than the 3 lager yeasts. Neither MYGP + Cu nor crystal violet could detect all the wild Saccharomyces species tested but the proportion detected by each was similar. Twenty-seven out of 28 non-Saccharomyces wild yeasts tested could be detected in MYGP + Cu. When brewery samples were examined, the detection rate by MYGP + Cu compared favourably with that by a combination of crystal violet and lysine. MYGP + Cu is particularly suited to the monitoring of the production of cask-conditioned ales.