Anti yeast activities of some essential oils in growth medium, fruit juices and milk

The anti-yeast activities of four essential oils (EOs) from clary sage, juniper, lemon and marjoram against wild-type isolates of the food-related yeasts Geotrichum candidum, Pichia anomala, Saccharomyces cerevisiae and Schizosaccharomyces pombe in malt extract (ME) medium, apple juice and milk were investigated. Minimal inhibitory concentrations (MICs) for the EOs and their main components were determined and the checkerboard method was used to calculate fractional inhibitory concentration (FIC) indices for the combinations of EOs or components. The most sensitive yeast was S. pombe (MICs of 0.0625-0.125 μl/ml) while G. candidum proved to be the most insensitive (MICs of 0.5-2 μl/ml). In general, the lag phases were lengthened by increasing EO concentrations, while significant reduction of growth rates was obtained only at the highest EO concentrations. The anti-yeast effects of the EOs were good in the acidic pH range optimal for yeasts growth. Combinations of juniper and clary sage EOs resulted in additive effects in the case of S. cerevisiae and G. candidum, but all other combinations showed no interaction. The combination of α-pinene and limonene led to synergism, while the combination of α-pinene with linalool resulted in an additive effect. Cloudy apple juice protected the yeasts against the effect of lemon EO: the lag phases were shorter and the growth rates higher than in clear apple juice. Lemon EO decreased the growth rate of G. candidum in skimmed milk in a dose-independent manner. Our results show that by adding lemon EO to clear apple juice a new, harmonic taste can be achieved and open storage time could be prolonged.     

Identification of the major yeasts isolated from high moisture corn and corn silages in the United States using genetic and biochemical methods

The objective of this study was to identify species of yeasts in samples of high moisture corn (HMC) and corn silage (CS) collected from farms throughout the United States. Samples were plated and colonies were isolated for identification using DNA analysis. Randomly selected colonies were also identified by fatty acid methyl esters (FAME) and by physiological substrate profiling (ID 32C). For CS, Candida ethanolica, Saccharomyces bulderi, Pichia anomala, Kazachstania unispora, and Saccharomyces cerevisiae were the predominant yeasts. Pichia anomala, Issatchenkia orientalis, S. cerevisiae, and Pichia fermentans were the prevalent species in HMC. The 3 identification methods were in agreement at the species level for 16.6% of the isolates and showed no agreement for 25.7%. Agreement in species identification between ID 32C and DNA analysis, FAME and ID 32C, and FAME and DNA analysis was 41.1, 14.4, and 2.2%, respectively. Pichia anomala and I. orientalis were able to grow on lactic acid, whereas S. cerevisiae metabolized sugars (galactose, sucrose, and glucose) but failed to use lactic acid. The yeast diversity in CS and HMC varied due to type of feed and location. Differences in species assignments were seen among methods, but identification using substrate profiling generally corresponded with that based on DNA analysis. These findings provide information about the species that may be expected in silages, and this knowledge may lead to interventions that control unwanted yeasts.     

Biodiversity and safety aspects of yeast strains characterized from vineyards and spontaneous fermentations in the Apulia Region,Italy

This work is the first large-scale study on vineyard-associated yeast strains from Apulia (Southern Italy). Yeasts were identified by Internal Transcribed Spacer (ITS) ribotyping and bioinformatic analysis. The polymorphism of interdelta elements was used to differentiate Saccharomyces cerevisiae strains. Twenty different species belonging to 9 genera were identified. Predominant on the grape surface were Metschnikowia pulcherrima, Hanseniaspora uvarum and Aureobasidium pullulans, whereas M. pulcherrima and H. uvarum were dominant in the early fermentation stage. A total of 692 S. cerevisiae isolates were identified and a number of S. cerevisiae strains, ranging from 26 to 55, was detected in each of the eight fermentations. The strains were tested for biogenic amines (BAs) production, either in synthetic media or grape must. Two Pichia manshurica, an Issatchenkia terricola and a M. pulcherrima strains were able to produce histamine and cadaverine, during must fermentation. The production of BAs in wine must was different than that observed in the synthetic medium. This feature indicate the importance of an “in grape must” assessment of BAs producing yeast. Overall, our results suggest the importance of microbiological control during wine-making to reduce the potential health risk for consumer represented by these spoilage yeasts.     

Taxonomic and molecular characterization of lactic acid bacteria and yeasts in nunu,a Ghanaian fermented milk product

Produced from raw unpasteurized milk, nunu is a spontaneously fermented yoghurt-like product made in Ghana and other parts of West Africa. Despite the importance of nunu in the diet of many Africans, there is currently only limited information available on the microorganisms associated with nunu processing. With the aim of obtaining a deeper understanding of the process and as a first step towards developing starter cultures with desired technological properties for nunu production, a microbiological characterization of nunu processing in three different towns in the Upper East region of Ghana, namely Bolgatanga, Paga and Navrongo, was carried out. Lactic acid bacteria (LAB) and yeasts associated with nunu processing were isolated and identified using a combination of pheno- and genotypic methods including morphological and carbohydrate fermentation tests, (GTG)₅-based rep-PCR, multiplex PCR, and 16S and 26S rRNA gene sequencing. The LAB counts during nunu processing increased from 4.5 ± 0.4 log cfu/ml at 0 h to 8.7 ± 1.8 log cfu/ml at 24 h of fermentation while yeasts counts increased from 2.8 ± 1.2 log cfu/ml at 0 h to 5.8 ± 0.5 log cfu/ml by the end of fermentation. Lactobacillus fermentum was the dominant LAB throughout the fermentations with Lactobacillus plantarum and Leuconostoc mesenteroides playing prominent roles during the first 6–8 h of fermentation as well. Less frequently isolated LAB included Lactobacillus helveticus, Enterococcus faecium, Enterococcus italicus, Weissella confusa and a putatively novel Lactococcus spp. The yeasts involved were identified as Candida parapsilosis, Candida rugosa, Candida tropicalis, Galactomyces geotrichum, Pichia kudriavzevii and Saccharomyces cerevisiae with P. kudriavzevii and S. cerevisiae being the dominant yeast species.     

Effect of caraway,basil, and oregano extracts and their binary mixtures on fungi in growth medium and on shredded cabbage

In this study the effect of individual and binary mixtures of caraway, oregano and basil extracts on the growth of Cladosporium cladosporioides, Aspergillus wentii, Eurotium herbariorum, Penicillium aurantiogriseum and Fusarium verticillioides isolated from food was investigated. Caraway extract at a concentration of 0.70 mL/100 mL and basil extract at a concentration of 1.5 mL/100 mL were fungicidal (MFC) to C. cladosporioides, A. wentii, E. herbariorum and F. verticillioides, and inhibitory (MIC) to P. aurantiogriseum. Oregano extract at a concentration of 2.5 mL/100 mL showed minimal fungicidal effects (MFC) on the growth of C. cladosporioides, A. wentii, E. herbariorum and P. aurantiogriseum and partially inhibited the growth of F. verticillioides. Binary mixtures of extracts showed stronger inhibitory effects on the tested fungi in comparison to the individual extracts. Some of the tested mixtures exhibited synergistic effect on the inhibition of C. cladosporioides, A. wentii, E. herbariorum, and F. verticillioides growth with the FIC_index of 0.70–0.97.     

Identification and characterization of yeasts causing chalk mould defects on par-baked bread

Pichia anomala, Hyphopichia burtonii and Saccharomycopsis fibuligera are spoilage yeasts causing chalk mould defects on par-baked breads packaged under modified atmosphere. The first objective of this study was to identify yeasts isolated from spoiled par-baked breads by means of a RAPD protocol and to determine the dominant spoilers amongst identified strains. The second objective was to determine the effects of water activity (a_w) and pH value on the growth rates and lag phase durations of P. anomala, H. burtonii and S. fibuligera. 95% of the yeasts tested were identified as P. anomala and 5% as S. fibuligera, H. burtonii was not detected. In order to investigate the effect of a_w and pH the growth of the three yeasts was tested within an a_w range of 0.88-0.98 and a pH range of 2.8-8.0. P. anomala was able to grow from pH 2.8 to 8 without a clear optimum. S. fibuligera and H. burtonii showed a pH optimum for growth of 5. The optimum water activity for growth was different for the three strains and varied between 0.96 and 0.98. These growth data were further used to develop secondary models that describe the relationship between a_w and the radial or colony growth rate (g, mm/d) or the lag phase duration (λ, d). The identification of the spoilage organisms and a good understanding of the effects of a_w and pH on the growth behavior is essential for future development of adequate conservation strategies against chalk mould defects.     

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.     

Chemical fingerprinting and bioactivity of Amazonian Ecuador Croton lechleri Müll. Arg. (Euphorbiaceae) stem bark essential oil: A new functional food ingredient?

Croton lechleri essential oil has been obtained by steam distillation of fresh stem bark from Amazonian Ecuador adult plants (yield: 0.61 ml/kg [0.061%]; density: 1.01 g/ml), and then chemically characterised by GC (Gas Chromatography) and GC–MS (gas chromatography–mass spectrometry). Seventy-four chemicals were detected and identified; the most abundant in descending order, were the sesquiterpenes sesquicineole (17.29%), α-calacorene (11.29%), 1,10-di-epi-cubenol (4.75%), β-calacorene (4.34%) and epi-cedrol (4.09%). Monoterpenes checked with a relative peak area higher than 2.0% were α-pinene (2.01%), p-cymene (2.61%), limonene (4.20%) and borneol (2.67%). The structure of the main chemicals were confirmed by GC–MS and ¹H NMR analyses. Spectrophotometric 1,1-diphenyl-2-picrylhydrazyl (DPPH) and DPPH-(high performance) thin layer chromatography (DPPH-(HP)TLC) bioautographic assays showed a lower radical scavenging capacity (IC₅₀) with respect to commercial thyme essential oil and BHA (butylated hydroxyl anisole), pointing out, however, that the C. lechleri essential oil fraction, characterised by α-calacorene, β-calacorene and δ-cadalene, was the most involved in the bioactivity. Similar results were obtained with β-carotene bleaching assay, where the IC₅₀ values were 0.291 ± 0.024 mg/ml for C. lechleri essential oil, 0.164 ± 0.013 and 1.34 × 10⁻⁴ ± 10⁻⁵ mg/ml for thyme essential oil and BHA, respectively. (HP)TLC-bioautographic assay performed with Gram positive and Gram negative bacteria revealed a minimum inhibitory concentration (MIC) values comprised between 0.10 mg/ml (Escherichia coli) and 10.10 mg/ml (for e.g. Pseudomonas aeruginosa), and the fraction mainly characterised by sesquicineole (97.38%) as the most involved in antibacterial capacity. Ames test employing Salmonella typhimurium TA98 and TA100 with and without a metabolic activation mixture (S9 mix) demonstrated the absence of mutagenicity of the C. lechleri essential oil between a concentration range of 10⁻² and 100 mg/plate. The same results were achieved by Saccharomyces cerevisiae D7 strain assay. An interesting mutagen-protective efficacy was evidenced by a 30% and 33% revertants reduction of TA98 strain treated with 2-aminoanthracene and nitrofluorene (2 μg/plate), suggesting, above all, the possibility to employ C. lechleri essential oil as a new flavouring protective ingredient for foods or dietary supplements against potential mutagens formed during cooking and/or processing in general.     

Food-grade microemulsions and nanoemulsions: Role of oil phase composition on formation and stability

Lemon oil is widely used as a flavoring component in beverages, foods, cosmetics, and household products. Lemon oil comes in a variety of chemical compositions depending on its biological origin, extraction methods, and purification procedures. At present, there is a relatively poor understanding of the influence of lemon oil composition on its functional properties. In this study, we examined the influence of lemon oil fold (1×, 3×, 5× and 10×) on the formation and properties of oil-in-water microemulsions and nanoemulsions. The concentration of both polar (high water solubility and low log P) and non-polar (low-water solubility and high log P) components increased with increasing oil fold. The nature of the colloid dispersions formed was established using an emulsion titration method that involved titrating lemon oil droplets into a surfactant micelle solution (1% Tween 80). Oil fold affected the rate and extent of solubilization, as well as the stability of lemon oil droplets to growth. The maximum amount of lemon oil that could be solubilized within the micelles increased with increasing oil fold, as did the stability of lemon oil droplets to growth. The results were interpreted in terms of the ability of different lemon oil molecules to be incorporated within water or surfactant micelles, and the influence of lemon oil polarity on Ostwald ripening. This study provides valuable information about the relationship between lemon oil composition and its performance in colloidal delivery systems suitable for use in the food and beverage industries.     

Growth inhibition of tomato-rot fungi by phenolic acids and essential oil extracts of pepperfruit (Dennetia tripetala)

Phenolic and essential oil extracts of pepperfruit (Dennetia tripetala) showed antifungal activity against Saccharomyces cerevisiae, Saccharomyces sp., Candida tropicalis, Candida sp., Cryptococcus sp., Geotrichum sp., Rhizopus stolonifer, Aspergillus niger and Fusarium sp. isolated from spoilt tomato fruits and cultured on agar plates. Antifungal activity of phenolic and essential oil extracts was observed at inhibitory concentrations (IC) in the range of 2.5–6.5 and 1.5–3.0 mg/ml tomato/glucose medium respectively. Combination of phenolic and essential oil extracts at concentrations below IC values significantly retarded growth of fungi resident in blended freshly harvested and open market tomato fruits. These fungi were not detected in the tomato after 1 month storage when mild heat (80°C for 1 min) and NaCl (10 mg/g) were combined with the phenolic and essential oil extracts as preservative hurdles. The population of challenge fungi in blended tomato treated with the same low concentration of the extracts and salt but without heat hurdle, steadily declined till none was detected after 3 months. Being an edible fruit, pepperfruit extracts may prove a useful natural preservative in food processing.     

Dynamic study of yeast species and Saccharomyces cerevisiae strains during the spontaneous fermentations of Muscat blanc in Jingyang,China

The evolution of yeast species and Saccharomyces cerevisiae genotypes during spontaneous fermentations of Muscat blanc planted in 1957 in Jingyang region of China was followed in this study. Using a combination of colony morphology on Wallerstein Nutrient (WLN) medium, sequence analysis of the 26S rDNA D1/D2 domain and 5.8S-ITS-RFLP analysis, a total of 686 isolates were identified at the species level. The six species identified were S. cerevisiae, Hanseniaspora uvarum, Hanseniaspora opuntiae, Issatchenkia terricola, Pichia kudriavzevii (Issatchenkia orientalis) and Trichosporon coremiiforme. This is the first report of T. coremiiforme as an inhabitant of grape must. Three new colony morphologies on WLN medium and one new 5.8S-ITS-RFLP profile are described. Species of non-Saccharomyces, predominantly H. opuntiae, were found in early stages of fermentation. Subsequently, S. cerevisiae prevailed followed by large numbers of P. kudriavzevii that dominated at the end of fermentations. Six native genotypes of S. cerevisiae were determined by interdelta sequence analysis. Genotypes III and IV were predominant. As a first step in exploring untapped yeast resources of the region, this study is important for monitoring the yeast ecology in native fermentations and screening indigenous yeasts that will produce wines with regional characteristics.     

Production of white pan bread leavened by Pichia anomala SKM-T

Pichia anomala SKM-T was used as a starter for making white pan bread to extend the shelf-life and to improve flavor properties. Baking qualities were determined from P. anomala SKM-T leavened bread (PA) and Saccharomyces cerevisiae leavened bread (CO). Springiness and chewiness of the PA were significantly higher than those of the CO. The number of Penicillium paneum colonies on the bread surface for PA was significantly lower than for CO during the storage time (10 days). Based on sensory evaluation, a significant difference was detected between the 2 bread types in flavor category. A total 16 flavor compounds were detected only in PA, including phenylethyl alcohol and 2-phenylethyl acetate, which have antifungal activities. P. anomala SKM-T is a feasible leavening agent for the production of white pan bread with an extended shelf-life.     

Essential oil composition,antimicrobial and antioxidant activities of Satureja cuneifolia Ten.

Satureja cuneifolia Ten. is a well-known aromatic plant which is frequently used as a spice and herbal tea in Anatolia. S. cuneifolia oil was analyzed by gas chromatography/mass spectrometry (GC/MS). The major components of S. cuneifolia oil were carvacrol (44.99%) and p-cymene (21.61%). The essential oil of S. cuneifolia exhibited antimicrobial activity against all of the tested foodborne and spoilage bacteria. The minimum inhibitory concentration (MIC) values for test bacteria which were sensitive to the essential oil of S. cuneifolia were in the range of 600–1400 μg/ml. Antioxidant activities of the essential oil and the methanolic extract from S. cuneifolia were evaluated by using DPPH radical scavenging, β-carotene–linoleic acid bleaching and metal chelating activity assays. In addition, the amounts of total phenol components in the plant methanolic extract (222.5 ± 0.5 μg/mg) and the oil (185.5 ± 0.5 μg/mg) were determined.     

Chemical composition,antioxidant and antimicrobial activities of essential oil obtained from Ferula assa-foetida oleo-gum-resin: Effect of collection time

The properties of essential oils obtained from Ferula assa-foetida oleo-gum-resins (OGRs) collectioned in three collections times in 15 June (OGR1), 30 June (OGR2) and 15 July (OGR3) 2011 was investigated. Essential oil from OGR1 was constituted high levels of (E)-1-propenyl sec-butyl disulfide (23.9%) and 10-epi-γ-eudesmol (15.1%). Essential oil from OGR2 was constituted high levels of (Z)-1-propenyl sec-butyl disulfide (27.7%) and (E)-1-propenyl sec-butyl disulfide (20.3%). Essential oil from OGR3 was constituted high levels of β-pinene (47.1%) and α-pinene (21.3%). Inhibitory concentration (IC50) for radical scavenging were 0.012–0.035, 0.025–0.047 and 0.035–0.066 mg/ml of essential oil obtained from OGR1, OGR2 and OGR3, respectively. Minimal inhibitory concentration (MIC) for Gram-positive and Gram-negative bacteria and fungi grpwth were 0.028–0.111, 0.027–0.107 and 0.018–0.058 mg/ml of essential oil obtained from OGR1, OGR2 and OGR3, respectively. Essential oils obtained from different OGRs have different composition and biological activity thus have different applications in food and health industry.     

In vitro antimicrobial effects and mechanism of action of selected plant essential oil combinations against four food-related microorganisms

The aim of this study was to evaluate the antimicrobial efficacy of selected plant essential oil (EO) combinations against four food-related microorganisms. Ten EOs were initially screened against Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Saccharomyces cerevisiae using agar disk diffusion and broth dilution methods. The highest efficacy against all the tested strains was shown when testing the oregano EO. EOs of basil and bergamot were active against the Gram-positive bacteria (S. aureus and B. subtilis), while perilla EO strongly inhibited the growth of yeast (S. cerevisiae). The chemical components of selected EOs were also analyzed by GC/MS. Phenols and terpenes were the major antimicrobial compounds in oregano and basil EOs. The dominant active components of bergamot EO were alcohols, esters and terpenes. For perilla EO, the major active constituents were mainly ketones. The checkerboard method was then used to investigate the antimicrobial efficacy of EO combinations by means of the fractional inhibitory concentration index (FICI). Based on an overall consideration of antimicrobial activity, organoleptic impact and cost, four EO combinations were selected and their MIC values were listed as follows: oregano–basil (0.313–0.313 μl/ml) for E. coli, basil–bergamot (0.313–0.156 μl/ml) for S. aureus, oregano–bergamot (0.313–0.313 μl/ml) for B. subtilis and oregano–perilla (0.313–0.156 μl/ml) for S. cerevisiae. Furthermore, the mechanisms of the antimicrobial action of EO combinations to the tested organisms were studied by the electronic microscopy observations of the cells and the measurement of the release of cell constituents. The electron micrographs of damaged cells and the significant increase of the cell constituents' release demonstrated that all EO combinations affected the cell membrane integrity.     

Phytochemical and Antimicrobial Evaluation of Aqueous and Organic Extracts of Calotropis procera Ait Leaf and Latex

The aqueous and ethanol extract of Calotropis procera leaf and latex were investigated. The leaves and latex from the plant were tested for antimicrobial activities. The bioactive constituents extracted from the leaf and latex were tested against pathogenic organisms (Eschericia coli, Salmonella typhi, Bacillius subtilis, Candida albicans, Aspergillus niger) using the Agar well diffusion method. The ethanolic latex extract showed significant activity against all the test organisms. The results revealed that ethanol is a more effective extractive solvent for antimicrobial activity of leaf and latex of C. procera. The ethanol extract of the latex gave the widest zone of inhibition (21 mm) against B. subtilis. All the extracts inhibit the growth of all the organisms except B. subtilis of which the aqueous extract has no effect. The Minimum Inhibitory Concentration (MIC) for the latex extract was between 3 and 7.5 mg/ml for bacteria, and 5.0 to 7.0 mg/ ml for fungi. For the leaf extract the MIC for bacteria was between 5.0 and 10.5 mg/ml and 11 and 15 mg/ml for fungi. The results also showed an increase in antimicrobial activity with increase in temperature. This study therefore revealed that C. procera latex extract demonstrated strong and better inhibitory activity on the test organisms than the leaf extract. These findings therefore provide an explanation for the traditional medicinal use of C. procera extracts.     

Molecular ecology and polyphasic characterization of the microbiota associated with semi-dry processed coffee (Coffea arabica L.)

This work was aimed at isolating and identifying the microbiota present during the semi-dry method of coffee processing using polyphasic methods and to evaluate microbial diversity with PCR-DGGE. Samples of Coffea arabica L. were collected during different processing stages in southern Minas Gerais, Brazil. The bacterial and fungal isolates were phenotypically characterised and grouped according to the ARDRA technique, in which the 16–23S and ITS1-5.8S regions of the rDNA were sequenced for species identification. The bacterial counts varied from 3.7 to 7 log CFU g⁻¹. The yeast counts ranged from 3.4 to 6.9 log CFU g⁻¹, and the filamentous fungal population varied from 2 to 3.7 log CFU g⁻¹. Bacillus subtilis, Escherichia coli, Enterobacter agglomerans, Bacillus cereus and Klebsiella pneumoniae were the predominant bacteria detected during the processing of the coffee, and Pichia anomala, Torulaspora delbrueckii and Rhodotorula mucilaginosa were the dominant yeasts. All of the yeast and bacterial species detected by PCR-DGGE were isolated using culture-dependent methods, with the exception of one uncultivable bacterial species. Aspergillus was the most common genus among the filamentous fungal isolates. The use of polyphasic methods allowed a better characterization of the microbiota that is naturally present in semi-dry processed coffee.     

Effects of pectinolytic yeast on the microbial composition and spoilage of olive fermentations

This study resulted in the identification of pectinolytic yeasts in directly brined Sicilian-style green olive fermentations and examination of the influence of those yeasts on the microbial composition and quality of fermented olives. Firstly, defective olives processed in Northern California from 2007 to 2008 and characterized by high levels of mesocarp tissue degradation were found to contain distinct yeast and bacterial populations according to DNA sequence-based analyses. Strains of (pectinolytic) Saccharomyces cerevisiae, Pichia manshurica, Pichia kudriavzevii, and Candida boidinii isolated from directly brined olives were then inoculated into laboratory-scale olive fermentations to quantify the effects of individual yeast strains on the olives. The pH, titratable acidity, and numbers of lactic acid bacteria (LAB) and yeasts varied between the fermentations and fermentations inoculated with P. kudriavzevii and C. boidinii promoted the development of LAB populations. Olive tissue structural integrity declined significantly within 30, 74, and 192 days after the inoculation of pectinolytic S. cerevisiae, P. manshurica and C. boidinii, respectively. In comparison, tissue integrity of olives in control fermentations remained intact although pectinolytic yeasts were present. Notably, pectinolytic yeasts were not found in fermentations inoculated with (non-pectinolytic) P. kudriavzevii and olives exposed to a 1:1 ratio of P. kudriavzevii and P. manshurica exhibited no significant tissue defects. This study showed that pectinolytic yeast are important components of directly brined green olive fermentations and damage caused by pectinolytic yeasts might be prevented by other microbial colonists of the olives.     

Assessment of pulsed electric fields induced cellular damage in Saccharomyces cerevisiae: Change in performance of mitochondria and cellular enzymes

Pulsed electric fields (PEF) induced cellular damage in Saccharomyces cerevisiae, mainly focusing on metabolic properties including performance of mitochondria and cellular enzymes, was evaluated in this study. The proportion of sublethally injured S. cerevisiae cells was around 90% after PEF treatment at 20 kV/cm for 100–500 μs. Sublethal injure S. cerevisiae correlated with damage to mitochondria and membranes caused by PEF, which was also confirmed by the glucose-energized repair process. An increase in plasma membrane Ca²⁺-ATPase, decrease of cytoplasmic esterase activity and changes of ten cellular enzymes of S. cerevisiae were observed after PEF treatment, suggesting the sublethal injury of S. cerevisiae is correlated with the inactivation or activation of cellular enzymes and aggregation of proteins under PEF treatment.     

Study on chemical composition and biological activities of essential oil and extract from Salvia pisidica

In this study, total contents of phenolic, flavanol and flavonol, antioxidant activities and antimicrobial activities of the Turkish endemic Salvia pisidica Boiss. & Heldr. ex Bentham (Lamiaceae) extract and essential oil were assessed in vitro. Total phenolic, flavanol and flavonol contents in the extract were 54.57 mg gallic acid equivalents (GAE)/g, 16.70 mg catechine equivalents (CE)/g and 18.19 mg rutin equivalents (RE)/g, respectively. Antioxidant activities (IC₅₀ value) of the extract and essential oil were determined as 4.88 and 6.41 mg/mL by DPPH assay, respectively. 31 compounds were determined in the essential oil using GC-MS and the major compounds (%) were camphor (23.76), sabinol (19.2), α-thujone (14.2) and eucalyptol (1.8-cineole) (5.8).The antimicrobial activity of the methanolic extract and the essential oil against 13 bacterial and two yeast strains was determined. The extract (concentration 5 g/100 ml or 10 g/100 ml) was effective against most of the strains tested, yet not against Bacillus cereus, Staphylococcus aureus, Aeromonas hydrophila and the two yeast strains tested. The essential oil (2 g/100 ml) showed an antimicrobial effect against all the gram (+) bacteria tested, against Saccharomyces cerevisiae, but was not effective against all gram (−) bacteria and Candida albicans. These results show that S.piscidica essential oil and extract could be considered as a natural alternative to traditional food preservatives and be used to enhance food safety and shelf life.