Food Spoilage Yeasts Research Articles

The effect of pH, sodium chloride, sucrose, sorbate and benzoate on the growth of food spoilage yeasts

The effects of pH, concentration of NaCl, concentration of sucrose and concentrations of sorbic and benzoic acids on growth were examined for 30 strains of food spoilage yeasts, representingDebaryomyces hansenii, Yarrowia lipolytica, Kloeckera apiculata, Zygosaccharomyces bailii, Zygosaccharomyces rouxii, Kluyveromyces marxianus, Pichia membranaefaciens, Pichia anomalaandSaccharomyces cerevisiae.Zygosaccharomyces bailiidid not grow at pH 7.0 andZ. rouxii, Kl. apiculataandP. membranaefaciensdid not grow at pH 8.0. OnlyKl. apiculatagrew at pH 1.5–2.0. The remaining species grew at pH 2.5–8.0. None of the species grew at 20% NaCl but strains ofD. hansenii, Z. rouxiiandP. anomalagrew at 15% NaCl.S. cerevisiaeandK. marxianuswere the least salt tolerant, showing no growth at 7.5% NaCl and 10% NaCl, respectively. Medium pH influenced growth in the presence of NaCl. ForY. lipolytica, D. hanseniiandS. cerevisiae, greatest tolerance of NaCl occurred at pH 5.0–7.0, but forKl.apiculata, D. membranaefaciensandZ. bailiibest tolerance occurred at pH 3.0.K. apiculatagrew in the presence of 12.5% NaCl at pH 2.0. All yeasts grew at 50% sucrose, withZ. rouxii, Z. bailiiandP. anomalaandD. hanseniigrowing at 60–70% sucrose. Medium pH in the range 2.0–7.0 had little effect on ability to grow in the presence of high sucrose concentrations.Z. bailiiandY. lipolyticawere the species most tolerant of sorbate and benzoate preservatives (750–1200 mg l−1) at pH 5.0.

Inhibitory effects of vanillin on some food spoilage yeasts in laboratory media and fruit purées

The effect of vanillin and essential oil of mint on the growth of different strains of food spoilage yeasts in laboratory media and fruit purées was studied. Growth of Saccharomyces cerevisiae, Zygosaccharomyces rouxii, Debaryomyces hansenii and Z. bailii was inhibited in culture media and apple purée containing 2000 ppm of vanillin for 40 days storage at 27 °C and a w 0.99 or 0.95. But 3000 ppm of the spice were not effective to inhibit Z. bailii growth in bananat purée. Growth of yeasts was not affected by 100 ppm of essential oil of mint.

Comparison of the inhibitory and lethal effects of synthetic versions of plant metabolites (anethole, carvacrol, eugenol, and thymol) on a food spoilage yeast(Debaromyces hansenii)

Abstract The inhibitory and lethal effects of synthetic versions of compounds found in common herbs and spices were compared on a food spoilage yeast Debaromyces hansenii. Separate treatments of trans‐anethole, carvacrol, eugenol, and thymol were investigated in potato dextrose broth (PDB) suspension cultures. Inhibitory activity was studied for all compounds at concentrations of 25, 50, 75, and 100 ppm over a 55 h incubation while lethality was investigated for trans‐anethole, carvacrol, and thymol at 100 and 125 ppm over a four day incubation. All compounds exhibited at least minor inhibitory activity at a concentration of 25 ppm. During the 55 h incubation period, the minimum concentration for total inhibition by trans‐anethole was 75 ppm, while that for carvacrol and thymol was 100 ppm. The maximum level of eugenol examined, 100 ppm, did not completely inhibit outgrowth. Growth curve data were described by the logistic equation which provided for quantitative comparison of inhibition. Lethality was achieved with trans‐anethole, carvacrol, and thymol at 100 and 125 ppm as determined by colony forming units (CFU) on potato dextrose agar (PDA) over four days incubation. These findings demonstrate an approach for quantitatively describing inhibition and evaluating the lethal effects of synthetic versions of plant metabolites on D. hansenii. This research may prove useful in future studies identifying active compounds, determining their effective concentrations, and providing strategies for the development of food applications.

A novel approach for discovering retrotransposons: characterization of a long terminal repeat element in the spoilage yeast Pichia membranaefaciens and its use in strain identification.

A novel PCR-based approach designed to detect retrotransposon long terminal repeat (LTR) elements via their association with tRNA genes was applied to Pichia membranaefaciens, an industrially important food spoilage yeast. A single primer based on tRNA gene sequences was used to amplify DNA fragments from different strains, and an observed fragment size difference among strains was found to correspond to the expected size of an integrated LTR. A 289-bp element was cloned as part of the larger fragment and shown to be present in a high copy number and variable genomic location in all strains examined. Sequence analysis revealed the element to be bounded by nucleotides TG at the 5' end and CA at the 3' end and to exhibit target site duplication and other sequence motifs diagnostic of retrotransposon LTRs. LTR sequence data enabled the development of a rapid identification method which distinguished among different strains. The novel method for LTR isolation and the strain identification system are both likely to prove generally applicable for a wide range of other organisms.

Use of indirect conductimetry to predict the growth of spoilage yeasts, with special consideration of Zygosaccharomyces bailii

In recent years, modeling for the purpose of predicting microbiological spoilage of foods has gained much interest. Predictive modeling requires a concentrated mathematical and experimental approach; to collect data of adequate quality is a technically demanding task when several experimental parameters are involved. Rapid, non-traditional, automated techniques are particularly useful in modeling. Of these, electrometric techniques appear to be most promising. Indirect conductimetry was used to study the effect of temperature, a w, automated Malthus 2000 instrument proved to be convenient for gathering a large amount of data that were then used to develop polynomial models describing the response of the yeasts to combinations of experimental factors in terms of conductimetric detection time and maximum rate of change in conductance. Results demonstrated that indirect conductimetry is suitable for monitoring the effect of environmental factors on the growth and activity of Z. bailii and perhaps other food spoilage yeasts.

Differetiation of the spoilage yeast Zygosaccharomyces bailii from other Zygosaccharomyces species using 18S rDNA as target for a non-radioactive ligase detection reaction

A non-radioactive PCR coupled ligase detection reaction was developed to discriminate the food spoilage yeasts Zygosaccharomyces bailii and Z. bisporus from each other and from other members of the genus. A short region of the 18S rRNA gene was amplified from boiled cell lysates and polymerase chain reaction (PCR) products used as target in the template directed ligation of two adjacent oligonucleotides. Ligated products were captured using biotin-streptavidin chemistry and detected using digoxigenin immuno-chemiluminescence. The ligase detection reaction was able to discriminate to the species level, targeting a single base deletion. The specificity of the reaction was assessed using seven species of the genus Zygosaccharomyces. Only strains of Z. bailii and Z. bisporus gave positive results with their respective primer sets. The lower detection limit of the strategy was 10pg (3 x 10(7) targets) of amplified product.

Resistance of food spoilage yeasts to sorbic acid

About 100 strains isolated from spoiled foods and beverages were screened for their ability to grow in the presence of successively higher concentrations of sorbic acid. Most strains were able to grow at 150 ppm, 40% at 500 ppm and remarkably two strains of Zygosaccharomyces bailii tolerated 800 ppm. Significant differences were observed between strains of the same species. A general observation was that increasing concentration of sorbic acid resulted in a decrease in the biomass present at the stationary phase and increase in the duration of the lag phase.

Isolation of Food Spoilage Yeasts from Salads Purchased from Delicatessens

Reports on a study of the bacteriological and mycological quality of 87 prepared salads purchased from delicatessens. Bacterial counts were generally low. Of the 87 salads, only 19 per cent had plate counts greater than 104 organisms/g. Coliforms were isolated from three samples, E. coli from one and Listeria monocytogenes from one. By contrast yeasts were isolated from 76 per cent of the salads and at counts greater than 104 organisms/g in 31 per cent. Twenty‐one different yeast species were isolated, of which the commonest were Saccharomyces dairensis and Saccharomyces exiguus. Few of the yeasts have any significant role in human disease. The commonest yeasts isolated, however, are associated with spoilage of mayonnaise‐based salads. Their isolation from these foods suggests inadequate temperature control.

Use of indirect conductimetry for predicting growth of food spoilage yeasts under various environmental conditions

Four variables (temperature,aw, pH and potassium sorbate concentration) at three levels were studied to determine their effects on the growth of six yeasts (Candida glabrata, Candida parapsilosis, Debaryomyces hansenii, Pichia membranaefaciens, Saccharomyces cerevisiae andZygosaccharomyces bailii) isolated from spoiled food products. The detection time (DT) and the maximum change in conductance (MRC) were measured by indirect conductimetry using a Malthus instrument. Temperature,aw and potassium sorbate concentration were the most important variables individually and in combination that affected yeast growth. Shelf life of fruit juice ataw≤0.96, pH≤3.8 and containing≤0.03% potassium sorbate, when stored at ≤10°C, would be predicted to be greatly extended.Z. bailii was the most resistant of the yeasts in terms of ability to tolerate stress conditions and is proposed as a test species to develop a predictive model for spoilage.

Rapid electrical methods for the detection and enumeration of food spoilage yeasts

Methods for the electrical detection of food spoilage yeasts have been investigated; these include direct conductance, direct capacitance and indirect conductance measurement. Although these methods can be used to detect and enumerate yeasts, the two direct methods must be linked to the correct growth medium. The optimum medium for direct conductance monitoring was found to be Yeast Carbon Base and ammoniun tartrate (CBAT), whereas either CBAT or Yeast Carbon Base and ammonium sulphate (CBAS) could be used for direct capacitance monitoring. CBAT could also be used in indirect conductance systems; however, in some cases a medium was not required in indirect systems, as the food sample itself provided growth requirements. Generally, a direct capacitance system was better than a direct conductance system for yeast detection and enumeration, as it detected more yeast species. Indirect conductance was equivalent to direct capacitance.

The sensitivity of vegetative cells and ascospores of some food spoilage yeasts to sanitisers

The relative tolerances of the vegetative cells and ascospore-rich suspensions of two yeast species to sanitisers commonly employed in the food industry were compared using a suspension test procedure. The yeasts. Saccharomyces cerevisiae and Pichia anomala had been isolated from a bakery environment and implicated as potential spoilage microorganisms. The sanitisers included two quaternary ammonium compounds, an amphoteric-based sanitiser and a hypochlorite. The test assessed the ability of the disinfecting agents to destroy the ascospore-rich populations within the times and concentrations recommended to sanitise surfaces in food production environments. Vegetative cells of S. cerevisiae were more sensitive than the vegetative cells of P. cerevisiae were more sensitive than the to be more susceptible to sanitiser challenge than the ascospore-containing populations.

Probability of growth of the spoilage yeast Zygosaccharomyces bailii in a model fruit drink system

A quantitative method for the prediction of the probability of growth of the food spoilage yeast Zygosaccharomyces bailii in a model fruit-drink system is described. A factorially designed experiment, employing a microtitre-plate system was used to assess the effect on growth of culture pH and fructose concentration (°brix) as well as the weak-acid preservatives benzoic acid, sorbic acid and sulphur dioxide. Probability of growth was approximated to a logistic generalized linear model allowing a polynomial equation relating concentrations of sorbic acid, benzoic acid, sulphur dioxide, °brix and hydrogen ions to a function of the probability of growth to be produced. The resulting equation demonstrates a synergistic effect between obrix level and weak-acid concentration which is pH dependent. By quantifying this and other interactions as well as single effects the present model can be a useful tool not only to assess existing preservative systems but also during product formulation.

A note on estimation of food spoilage yeasts by measurement of adenosine triphosphate (ATP) after growth at various temperatures.

The growth at 4 degrees, 10 degrees and 15 degrees C of six psychrotrophic yeasts isolated from foods was compared using total viable counts and ATP measurement. A linear relationship (r greater than or equal to 0.97) was obtained between log10 (number of viable yeasts) and log10 (ATP content) of cultures grown at these temperatures. This relationship was not temperature-dependent. The results are discussed and their significance for the rapid estimation of yeasts in foods is considered.

Induction of sporulation in food-spoilage yeasts

Four yeasts, Hansenula anomala, Kluyveromyces fragilis, Lodderomyces elongisporus and Saccharomyces cerevisiae, were cultured in two presporulation media at 30 ° C. Media consisted of yeast extract — peptone — acetate and yeast extract — peptone — dextrose broths. Except for K. fragilis, the test yeasts reached a high degree of sporulation when transferred to acetate- and ethanol-supplemented sporulation media. The percentage of S. cerevisiae cells forming asci was as high as 79% after 24 h incubation. H. anomala and L. elongisporus sporulated more rapidly in ethanol- compared to acetate-containing medium. Within test parameters, the concentration of acetate or ethanol, pH, and incubation temperature (25 ° C and 30 ° C) did not substantially influence the extent of sporulation.

Effects of Essential Oils from Plants on Growth of Food Spoilage Yeasts

ABSTRACTThirty‐two essential oils from plants were screened for inhibitory effects on 13 food‐spoilage and industrial yeasts. Of these, essential oils of allspice, cinnamon, clove, garlic, onion, oregano, savory, and thyme were most inhibitory. Oils were subsequently tested for their effects on biomass production and pseudomycelium formation of eight genera of yeasts. Garlic oil was a potent inhibitor of yeast growth at concentrations as low as 25 ppm. The oils of onion, oregano and thyme were also strongly inhibitory. Essential oils (100 ppm) had no effect on pseudomycelium production by Candida lipolytica. However, all eight essential oils delayed pseudomycelium formation by Hansenula anomala, whereas six oils stimulated pseudomycelium production by Lodderomyces elongisporus. Cinnamon and clove oils were clearly stimulatory to pseudomycelium production by Saccharomyces cerevisiae.

Salinity induced apoptosis in food spoilage yeast Zygosaccharomyces bisporus

Background: Food spoilage is one of the most serious challenges in agriculture, and food and beverage industry, which can lead to worldwide food economic loss. The crucial organoleptic species, Zygosaccharomyces bisporus, is a highly resistant yeast fungus that can escape industrial quality check. They survive high salt environments by undergoing immediate programmed cell death (PCD), which plays an important role in mediating adaptive responses to adverse environmental conditions. Production of reactive oxygen species (ROS) prompted by salt stress is an early event in apoptosis, which in later stage is associated with prime genomic degradation.Methodology: In this study, the tolerance mechanism to salt of Z. bisporus MTCC 4801 cells was investigated by serial dilution of exponential growth phase of the cells in 1.0M sodium chloride (NaCl) as salt stressor, and spotting on Yeast Peptone Dextrose Agar (YPDA) plates with incubation at 28oC for growth assessment and colony count. Transmission electron microscopy (TEM) was used to demonstrate characteristic ultrastructural hallmark features of apoptosis on Z. bisporus cells exposed to 1.0M NaCl at three different stress interval periods; 60, 90, and 120 minutes. Results: Growth of Z. bisporus cells on the YPDA plates was observed after 16 hours incubation period. Comparing the growths, Z. bisporus tolerated salt concentration below 1.0M NaCl but no growth was observed at 1.0M NaCl concentration indicating 1.0M NaCl to be limiting concentration for Z. bisporus growth. TEM analyses showed that treatment of Z. bisporus with 1.0M NaCl resulted in nuclear and cytoplasmic condensation, membrane blabbing, cytoskeletal distortion, and formation of apoptotic bodies. However, on prolonged stress span (90 and 120 minutes), the fungal cells were able to osmoadapt and repaired the damaged cells, resulting in lowering of the apoptotic ratio. Conclusion: These qualitative analyses contribute more insights regarding stress adaptive mechanisms in moderately halotolerant food spoilage yeast.Key words: Apoptosis; salt stress; food spoilage yeast; TEM; cell survival