Issatchenkia Occidentalis Research Articles

Prevention of microbes-induced spoilage in sodium chloride-free cucumber fermentations employing preservatives.

This study evaluated preservatives to stabilize sodium chloride (NaCl)-free-cucumber fermentations. The brining of air-purged laboratory cucumber fermentations with 100.0 mM calcium chloride (CaCl2 ) and 25.0 mM acetic acid resulted in immediate rises in pH, the chemical reduction of the medium, and malodors. Supplementation with 3.0 mM sodium benzoate or 3.0 mM potassium sorbate enabled a decline in pH, a continuous oxidative state of the medium, and delayed rising pH spoilage. However, lactic and acetic acids eventually disappeared in fermentations supplemented with preservatives. The amount of preservatives needed to suppress growth of brined-cucumber-spoilage microbes was determined in Fermented Cucumber Juice Medium (FCJM). Supplementation of FCJM with 10.0 mM sodium benzoate was inhibitory for the spoilage yeasts, Issatchenkia occidentalis and Pichia manshurica, and the lactobacilli, Lentilactobacillus buchneri and Lentilactobacillus parafarraginis, but not of Zygosaccharomyces globiformis. Potassium sorbate inhibited the spoilage yeasts at 15.0 mM in FCJM but not the lactobacilli. Supplementation of FCJM with 20.0 mM fumaric acid had a bactericidal effect on the spoilage-associated lactobacilli. As expected, NaCl-free-commercial cucumber fermentations brined with 100 mM CaCl2 , no acetic acid, and 6 mM potassium sorbate resulted in complete fermentations, but supported rising pH, microbially induced spoilage during long-term storage. Post-fermentation supplementation with 12 mM sodium benzoate, 10 mM fumaric acid, a combination of the two, or 10 mM fumaric acid and 2 mM AITC prevented microbial activity during long-term bulk storage. PRACTICAL APPLICATION: Several preservative-based strategies for stabilizing NaCl-free cucumber fermentation in a commercial production setting were developed, enabling the implementation of a processing technology that reduces wastewater volumes and environmental impact.

Occurrence of emerging multiresistant pathogens in the production chain of artisanal goat coalho cheese in Brazil

Sanitary-hygienic failures in cheese making can pose health risks to consumers. This study aimed to identify multiresistant pathogens in different production stages of artisanal goat coalho cheese in Brazil and characterize their phenotypic and genotypic resistance. Eleven properties in the state of Pernambuco, Brazil, participated in the study. Samples were obtained from different stages of production and the humans involved. The samples obtained were submitted to microbiological culture, then all the isolated microorganisms were submitted to the Matrix Associated Laser Desorption-Ionization - Time of Flight technique for the microbiological identification of the species. Subsequently, Staphylococcus spp., Enterococcus spp. and Macrococcus caseolyticus were subjected to polymerase chain reaction to search for resistance genes and disc diffusion technique to evaluate the resistance profile. A total of 111 isolates were obtained and 31 species were identified, with the frequency of Staphylococcus spp. (62.20%; 69/111), Enterococcus spp. (11.60%; 13/111), Macrococcus caseolyticus (10%; 11/111), Bacillus spp. (3.60%; 4/111), Enterobacter spp. (3.60%; 4/111), Aureobasidium pullulans (1.80%; 2/111), Corynebacterium camporealensis (1.80%; 2/111), Issatchenkia occidentalis (1.80%; 2/111), Kocuria kristinae (1.80%; 2/111), Aerococcus viridans (0.90%; 1/111) and Filifactor villosus (0.90%; 1/111). Phenotypic and genotypic resistance was also detected with the occurrence of 15.90% (7/44) of the mecA gene, 4% (1/25) vanA, and 4% (1/25) vanB in Staphylococcus spp. and 20% (2/10) vanB in and Enterococcus spp. Emerging multiresistant pathogens are present in the production chain of artisanal goat cheese and humans, who exert an important role in disseminating these bacteria with imminent risks to human health.

Identification and Characterization of Non-Saccharomyces Species Isolated from Port Wine Spontaneous Fermentations.

In winemaking, non-Saccharomyces yeast species contribute important organoleptic complexity. Current interest focuses on abundant and dominant strains characteristically present in the early phase of spontaneous alcoholic fermentations. Non-Saccharomyces species are particularly relevant in Port wine production such that the fermentation is prematurely stopped, after the metabolism of only one half of the available sugar, through fortification with aguardente. This work aimed to isolate, identify and characterize non-Saccharomyces species present in spontaneously fermenting Port. To accomplish these goals, yeasts were isolated from a selection of frozen must samples (2012–2016 harvests), using a pre-screening process choosing only the best candidates based on the organoleptic quality of the corresponding fortified wine. From five hundred non-Saccharomyces isolates, twelve species were identified. The three most abundant species, Hanseniaspora uvarum, Lachancea thermotolerans, and Metschnikowia pulcherrima, representing 89% of the isolates, exhibited particularly high diversity with high growth performance variability when exposed to typical stress conditions associated with common enological parameters. Less abundant species included Issatchenkia orientalis, Torulaspora delbrueckii, Hanseniaspora vineae, Hanseniaspora osmophila, Candida zemplinina, Rhodotorula mucilaginosa, Hanseniaspora guilliermondii, Issatchenkia occidentalis, and Zygosaccharomyces bisporus. This is the first study providing insights into the identification and characterization of non-Saccharomyces species responsible for spontaneous Port wine production.

Probiotic Yeasts Inhibit Virulence of Non-albicans Candida Species.

Systemic infections of Candida species pose a significant threat to public health. Toxicity associated with current therapies and emergence of resistant strains present major therapeutic challenges. Here, we report exploitation of the probiotic properties of two novel, food-derived yeasts, Saccharomyces cerevisiae (strain KTP) and Issatchenkia occidentalis (strain ApC), as an alternative approach to combat widespread opportunistic fungal infections. Both yeasts inhibit virulence traits such as adhesion, filamentation, and biofilm formation of several non-albicans Candida species, including Candida tropicalis, Candida krusei, Candida glabrata, and Candida parapsilosis as well as the recently identified multidrug-resistant species Candida auris They inhibit adhesion to abiotic surfaces as well as cultured colon epithelial cells. Furthermore, probiotic treatment blocks the formation of biofilms of individual non-albicans Candida strains as well as mixed-culture biofilms of each non-albicans Candida strain in combination with Candida albicans The probiotic yeasts attenuated non-albicans Candida infections in a live animal. In vivo studies using Caenorhabditis elegans suggest that exposure to probiotic yeasts protects nematodes from infection with non-albicans Candida strains compared to worms that were not exposed to the probiotic yeasts. Furthermore, application of probiotic yeasts postinfection with non-albicans Candida alleviated pathogenic colonization of the nematode gut. The probiotic properties of these novel yeasts are better than or comparable to those of the commercially available probiotic yeast Saccharomyces boulardii, which was used as a reference strain throughout this study. These results indicate that yeasts derived from food sources could serve as an effective alternative to antifungal therapy against emerging pathogenic Candida species.IMPORTANCE Non-albicans Candida-associated infections have emerged as a major risk factor in the hospitalized and immunecompromised patients. Besides, antifungal-associated complications occur more frequently with these non-albicans Candida species than with C. albicans Therefore, as an alternative approach to combat these widespread non-albicans Candida-associated infections, here we showed the probiotic effect of two yeasts, Saccharomyces cerevisiae (strain KTP) and Issatchenkia occidentalis (ApC), in preventing adhesion and biofilm formation of five non-albicans Candida strains, Candida tropicalis, Candida krusei, Candida glabrata, Candida parapsilosis, and Candida auris The result would influence the current trend of the conversion of conventional antimicrobial therapy into beneficial probiotic microbe-associated antimicrobial treatment.

Probiotic Effects of Yeasts on Virulence of Candida Species

Antifungal resistance and life‐threatening systemic infections of Candida species pose a major therapeutic challenge. As an alternative approach to combat this wild spread opportunistic fungal infection, we are investigating the probiotic effects of two yeasts Saccharomyces cerevisiae (strain KTP) an Issatchenkia occidentalis (strain ApC) against pathogenic Candida species. These yeasts were isolated from toddy and apple juice respectively. Their ability to prevent virulence traits such as adhesion, morphological transition and biofilm formation were studied. In this study, we focused on Candida albicans, Candida tropicalis, Candida krusei, Candida glabrata and Candida parapsilosis as test organisms. Probiotic effects were assessed using in vitro (simulated gastrointestinal conditions), ex vivo (Caco‐2 cell line) and in vivo (Caenorhabditis elegans) models. The results indicate that yeasts S. cerevisiae and I. occidentalis exhibited higher tolerance to simulated gastrointestinal juices as compared to Saccharomyces cerevisiae var. boulardii, a commercialised probiotic yeast. In the presence of S. cerevisiae and I. occidentalis, pathogenic fungi of the Candida species showed decreased virulence traits of surface adhesion and filamentation as compared to probiotic control strain S. boulardii. Finally, in vivo studies using C. elegans infection assay suggests that the novel probiotic yeasts protect the animal during infection. Together these results reveal the potential biotherapeutic potential of these novel yeasts against Candida infections.Support or Funding InformationLK received a fellowship under the program DST‐INSPIRE, Govt. of India and Fulbright‐Nehru doctoral program, USIEF, India. This work is partially supported by NIH‐NCCIH 1R15AT009926‐01 grant to RPR.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Sucrose and sorbitol supplementation on maltodextrin encapsulation enhance the potential probiotic yeast survival by spray drying

Abstracts Two potential probiotic yeasts Saccharomyces cerevisiae (strain KTP) and Issatchenkia occidentalis (ApC) were microencapsulated using maltodextrin and sucrose or sorbitol with an aim to improve its effectiveness by spray drying. Commercialized probiotic yeast Saccharomyces cerevisiae var. boulardii (NCDC 363) was used as a reference yeast in the study. The efficiency of the encapsulation was evaluated by yeast viability, and physical parameters such as yield, water activity, particle size and shape of the microcapsule. Furthermore, simulated gastrointestinal juice was used to estimate the protective effect of the matrix in the digestive system. Results indicated that sucrose or sorbitol incorporated maltodextrin microcapsules achieved 35–45% of increment in the viability of yeasts NCDC 363, KTP and ApC than maltodextrin alone encapsulated group. The encapsulated yeast was remarkably improved its growth in simulated gastrointestinal condition (32–64% in gastric and 46–80% in bile juice) as compared to the non-encapsulated yeast. However, we did not find any observable difference in growth among encapsulated groups in the gastrointestinal survival assay. The study provided an evidence for incorporation of sucrose and sorbitol enhance the maltodextrin encapsulation efficiency by spray drying.

Antagonistic effect of Saccharomyces cerevisiae KTP and Issatchenkia occidentalis ApC on hyphal development and adhesion of Candida albicans.

The morphological transition from yeast to a hyphal form, as well as the adhesion capability to the gastrointestinal tract, are implicated virulent determinant in Candida albicans and could be potential targets for prevention of the opportunistic pathogen. Based on this rationale, two yeast strains Saccharomyces cerevisiae KTP and Issatchenkia occidentalis ApC along with reference strain Saccharomyces boulardii NCDC 363 were screened for the probiotic potential. Characters like pH, temperature, bile, simulated gastrointestinal juice tolerance tests, and Caco-2 cell line adhesion assay were determined in the present study. Further, the evaluation of its impact on C. albicans morphological transition and adhesion was assessed using microtitre germ tube test. In terms of probiotic characteristics, both the strains were tolerant to pH 2.5 and the presence of bile (0.3 to 0.6%) with an optimum growth temperature of 37°C. The strain KTP was also resistant to simulated gastric and intestinal juices as compared to control (13% and 41%, respectively) and NCDC 363 (55% and 35%, respectively). In contrast, both the yeasts had reduced adhesiveness to Caco-2 monolayer. Candida virulence in in vitro systems indicated that treatment of live probiotic yeast cells (108ml) effectively reduced the filamentation and adhesion of C. albicans. The S. cerevisiae KTP had a profound effect on the hyphal development and adhesion when compared to the ApC and NCDC 363. The strain significantly reduced (P < .05) the hyphal growth in co-cultivated (93% and 94%, respectively) and pre-existing hyphae (54% and 68%) of strains C. albicans 183 and 1151. Isolates KTP and ApC also reduced the adhesion (≈ 22% and 41%, respectively) and transition of blastoconidia at two hours of incubation in abiotic surface. This study provides knowledge on the effect of potential probiotic yeasts such as Saccharomyces and non- Saccharomyces strains against virulence characteristic of Candida albicans.

Selection and use of indigenous mixed starter cultures for mustard leaves fermentation and the improvement of cuocai characteristics

To improve the characteristics and safety of traditional cuocai, the selection and use of mixed starter cultures is important. This study aimed to isolate the main indigenous lactic acid bacteria (LABs) and yeast species from spontaneous fermented mustard leaves, and they were used as starter cultures to ferment mustard leaves. Five predominant LABs, namely Q-1 (Enterococcus faecalis), G-1 (Lactobacillus plantarum), G-3 (Lactobacillus pentosus), and G-2 and G-4 (Lactobacillus buchneri) strains, and the two yeast strains J-1 (Issatchenkia orientalis) and J-2 (Issatchenkia occidentalis) were isolated from cuocai. From the results, Lb. plantarum and I. orientalis strains exhibited strong growth ability, fast acidification, and potent low-pH tolerance. Therefore, they were chosen as the mixed starter cultures to ferment mustard leaves. During the process of culture-dependent fermented mustard leaves, the changes of acidity, total crude protein, and total sugar were similar to those of culture-independent fermented mustard leaves, while the nitrite content of culture-dependent fermented mustard leaves was significantly lower than that of culture-independent fermented cuocai. According to gas chromatography-mass spectrometry analysis, the main volatile flavor compounds of fermented mustard leaves were alcohols, aldehydes, esters, and sulfides. There was no significant difference of volatile flavor compounds between the processes of culture-dependent and culture-independent fermentations. Therefore, it was suggested that Lb. plantarum and I. orientalis strains could be used to ferment cuocai instead of the traditional ferment method to control the quality and shelf safety of cuocai. © 2017 Society of Chemical Industry.

Effect of yeasts on biodegradation potential of immobilized cultures of white rot fungi

The aim was to investigate the effect of yeast organisms on the degradation process by immobilized cultures of ligninolytic fungi. Immobilization was accomplished by 7-day colonization of polyamide mesh with mycelial fragments. Irpex lacteus decolorized >90% of the initial concentration of 150mgl−1 of anthraquinone Remazol Brilliant Blue R dye in three subsequent decolorization cycles and the degradation capacity was not negatively affected by the presence of 106Saccharomyces cerevisiae cells per ml in the mixed culture. The yeast was not able to degrade the dye. I. lacteus biofilm was also resistant to bacterial infection with E. coli. Inoculation of the yeast to pre-formed I. lacteus biofilm culture resulted in a reduction of fungal biomass by 27%. Levels of LiP, MnP and laccase of I. lacteus were not much influenced by S. cerevisiae or E. coli. Similar resilience of P. ostreatus biofilms was observed after exposure to yeast Issatchenkia occidentalis when the fungal degradation capacity measured with Reactive Orange 16 azo dye was maintained over two decolorization cycles. I. occidentalis did not degrade the dye under the conditions used. Formation of densely packed fungal biofilms with abundant extracellular polysaccharide was not impeded by the yeast. Increase of MnP and laccase levels attributable to the presence of I. occidentalis was observed.

English

Variability exists in raw materials and processing methods used to produce household traditional opaque beers in Zimbabwe, resulting in beers of variable quality, depending on fermenting micro-organisms involved. Yeasts are important in determining the alcohol content, nutrition and organoleptic properties of the beers. This study aimed at determining the diversity and characteristics of the predominant yeasts isolated from a variety of beers collected from rural households in different geographical localizations. Predominant yeasts from 13 beer samples were characterized using morphological, biochemical and physiological tests. A total of 14 morphologically different yeasts were isolated. Yeast counts in the beer samples ranged from 7.87 to 9.56 log colony forming units/ml. From the 14 yeast isolates, a total of 11 yeasts were identified to species level. Saccharomyces cerevisiae was the predominant species identified in the beers. Other yeast species identified in the beers were Issatchenkia occidentalis, Kluyveromyces marxianus, Candida glabrata and Sporobolomyces holsaticus. Two yeast isolates were identified as belonging to the genus Rhodotorula. Ten of the isolates were able to ferment at least one of the fermentation substrates D-glucose, D-galactose, maltose, sucrose and raffinose, while three isolates were incapable of fermenting any of the fermentation substrates used. None of the isolates were able to ferment lactose. Five of the S. cerevisiae isolates were able to grow at 40°C while K. marxianus was the only isolate capable of growing at 45°C. Key words: Yeasts, characterisation, traditional opaque beer.

Correlation between ethanol stress and cellular fatty acid composition of alcohol producing non-Saccharomyces in comparison with Saccharomyces cerevisiae by multivariate techniques.

Wine production is a complex process both from biochemical and microbiological point of view in which yeast plays a central role. The use of the wine yeast Saccharomyces cerevisiae and non- Saccharomyces yeasts as mixed starter cultures for wine fermentations is of increasing interest to enhance the quality of wine.The most common stress, yeast cells encounter during wine fermentation is the increase in ethanol concentration.To enhance ethanol tolerance, alteration in the cellular lipid composition is one of its defence mechanism. Ethanol tolerance and cellular fatty acid composition of alcohol producing non Saccharomyces forms were compared with enological strains of Sacccharomyces cerevisiae. Saccharomyces cerevisiae used for the study, tolerated 15% of ethanol and the non Saccharomyces strains such as, Issatchenkia occidentalis and Issatchenkia orientalis tolerated 10% of ethanol. On exposure of Saccharomyces cerevisiae to ethanol stress, the proportion of monounsaturated fatty acids increased with concomitant decrease in saturated fatty acids. Decrease in monounsaturated fatty acids, exhibited by non-Saccharomyces yeasts when exposed to ethanol stress, could be one of the reasons for their inability to withstand more than 10% of alcohol. Multivariate techniques of data analysis - principal component analysis and linear discriminant analysis were employed in order to establish differentiation criteria as function of yeast strains, alcohol stress and their fatty acid profile. Based on the data, Chemometrics, such as principal component analysis and discriminant function analysis, can be successfully applied to fatty acid data to categorize the yeast.

Mycological Characteristics of Nine Unrecorded Yeasts from Flowers in the Orchard of Yesan-gun, Chungcheongnam-do and Hanbat Arboretum in Daejeon City, Korea

Six unrecorded yeasts, Cryptococcus festucosus 41-3, Cryptococcus heveanensis 56-4, Debaryomyces nepalensis 95- 4, Issatchenkia occidentalis 142-1, Dioszegia zsoltii 39-1, and Kwoniella europala 47-2 were screened from 108 yeasts isolated from flowers and fruits in orchards of Yesan-gun, Chungcheongnam-do, Korea. The morphological and cultural characteristics of these unrecorded yeasts were investigated. They had various shapes, including ellipsoidal, globose, and oval, and also had budding mode in vegetable reproduction, except I. occidentalis 142-1 (fission mode). K. europaea 47-2 only formed pseudomy- celium. D. zsoliti 39-1 did not grow in yeast extract-malt extract medium, potato dextrose medium, and vitamin-free medium. C. festucosus 41-3 grew well in 5% NaCl-containing yeast extract-peptone-dextrose medium and had a growth pH range of 7.0~ 10.0. Three unrecorded yeasts Ogataea polymorpha HB45-1, Rhodotonula hinnulla HB62-2, and Cryptococcus rajasthanensis HB80-4 were screened from 51 yeasts isolated from flowers in Hanbat arboretum in Daejeon city, Korea. They were globose in shape and did not form pseudomycelium. In addition, O. polymorpha HB45-1 and C. rajasthanensis HB80-4 had budding mode in vegetable reproduction. All of them grew well in vitamin-free medium and C. rajasthanesis HB80-4 also grew in 50% glucose and 5% NaCl-containing YPD medium.

Yeasts from kefir grains: isolation, identification, and probiotic characterization

Kefir-a traditional beverage whose consumption has been associated with health benefits-is a logical natural product to investigate for new probiotic strains. The aim of the present work was to isolate and identify kefir yeasts and select those with acid and bile tolerance to study their adhesion to epithelial cells and their transit through mouse gut. From 4 milky and 3 sugary kefir grains, 34 yeast strains were isolated and identified by means of classical microbiological and molecular-genetic methods (whole-cell protein pattern, internal-transcribed-spacer amplification, and analysis of restriction-fragment-length polymorphisms). We identified 4 species belonging to 3 genera-Saccharomyces cerevisiae (15 strains), Saccharomyces unisporus (6 strains), Issatchenkia occidentalis (4 strains), and Kluyveromyces marxianus (9 strains)-and selected 13 strains on the basis of resistance to low pH and bile salts. Among the strains selected, Kluyveromyces marxianus CIDCA 8154 and Saccharomyces cerevisiae CIDCA 8112 were further studied. Both strains evidenced the capacity to adhere to epithelial intestine-derived cells in vitro and to survive passage through the gastrointestinal tract of BALB/c mice. The investigation of the potential probiotic features of these kefir-yeast strains should be useful for the development of novel functional foods.

Yeast Diversity Isolated from Grape Musts During Spontaneous Fermentation from a Brazilian Winery

Saccharomyces and non-Saccharomyces yeast species from a winery located in Brazil were identified by ribosomal gene-sequencing analysis. A total of 130 yeast strains were isolated from grape surfaces and musts during alcoholic fermentation from Isabel, Bordeaux, and Cabernet Sauvignon varieties. Samples were submitted to PCR-RFLP analysis and genomic sequencing. Thirteen species were identified: Candida quercitrusa, Candida stellata, Cryptococcus flavescens, Cryptococcus laurentii, Hanseniaspora uvarum, Issatchenkia occidentalis, Issatchenkia orientalis, Issatchenkia terricola, Pichia kluyveri, Pichia guilliermondii, Pichia sp., Saccharomyces cerevisiae, and Sporidiobolus pararoseus. A sequential substitution of species during the different stages of fermentation, with a dominance of non-Saccharomyces yeasts at the beginning, and a successive replacement of species by S. cerevisiae strains at the final steps were observed. This is the first report about the yeast distribution present throughout the alcoholic fermentation in a Brazilian winery, providing supportive information for future studies on their contribution to wine quality.

Characteristics of spoilage-associated secondary cucumber fermentation.

Secondary fermentations during the bulk storage of fermented cucumbers can result in spoilage that causes a total loss of the fermented product, at an estimated cost of $6,000 to $15,000 per affected tank. Previous research has suggested that such fermentations are the result of microbiological utilization of lactic acid and the formation of acetic, butyric, and propionic acids. The objectives of this study were to characterize the chemical and environmental conditions associated with secondary cucumber fermentations and to isolate and characterize potential causative microorganisms. Both commercial spoilage samples and laboratory-reproduced secondary fermentations were evaluated. Potential causative agents were isolated based on morphological characteristics. Two yeasts, Pichia manshurica and Issatchenkia occidentalis, were identified and detected most commonly concomitantly with lactic acid utilization. In the presence of oxygen, yeast metabolic activities lead to lactic acid degradation, a small decline in the redox potential (E(h), Ag/AgCl, 3 M KCl) of the fermentation brines, and an increase in pH to levels at which bacteria other than the lactic acid bacteria responsible for the primary fermentation can grow and produce acetic, butyric, and propionic acids. Inhibition of these yeasts by allyl isothiocyanate (AITC) resulted in stabilization of the fermented medium, while the absence of the preservative resulted in the disappearance of lactic and acetic acids in a model system. Additionally, three Gram-positive bacteria, Lactobacillus buchneri, a Clostridium sp., and Pediococcus ethanolidurans, were identified as potentially relevant to different stages of the secondary fermentation. The unique opportunity to study commercial spoilage samples generated a better understanding of the microbiota and environmental conditions associated with secondary cucumber fermentations.

Biological detoxification of different hemicellulosic hydrolysates using Issatchenkia occidentalis CCTCC M 206097 yeast

This work had as its main objective to contribute to the development of a biological detoxification of hemicellulose hydrolysates obtained from different biomass plants using Issatchenkia occidentalis CCTCC M 206097 yeast. Tests with hemicellulosic hydrolysate of sugarcane bagasse in different concentrations were carried out to evaluate the influence of the hydrolysate concentration on the inhibitory compounds removal from the sugarcane bagasse hydrolysate, without reduction of sugar concentration. The highest reduction values of inhibitors concentration and less sugar losses were observed when the fivefold concentrated hydrolysate was treated by the evaluated yeast. In these experiments it was found that the high sugar concentrations favored lower sugar consumption by the yeast. The highest concentration reduction of syringaldehyde (66.67%), ferulic acid (73.33%), furfural (62%), and 5-HMF (85%) was observed when the concentrated hydrolysate was detoxified by using this yeast strain after 24 h of experimentation. The results obtained in this work showed the potential of the yeast Issatchenkia occidentalis CCTCC M 206097 as detoxification agent of hemicellulosic hydrolysate of different biomass plants.

Main microorganisms involved in the fermentation of Ugandan ghee

Ghee is widely produced from a traditional fermented butter-like product named mashita in western Uganda. However, no detailed studies have been done to identify the microorganisms involved in mashita fermentation. The aim of this study was to identify the microorganisms present at the end of mashita ripening using culture-dependent and culture-independent techniques. The most commonly identified species of lactic acid bacteria (LAB) in mashita using culture-dependent techniques were Lactobacillus paracasei, Lactobacillus helveticus, Lactobacillus plantarum and Lactobacillus perolens constituting 37.3%, 10.1%, 8.1% and 7.7% of total bacterial colonies isolated respectively. L. paracasei was the only bacterial species identified in all mashita samples by culture-dependent technique. Two of the four most commonly isolated LAB species ( L. helveticus and L. plantarum) were also identified in mashita by a culture-independent method (PCR-DGGE). Other main LAB species identified in mashita by PCR-DGGE were Bifidobacterium sp., Enterococcus faecium, Lactobacillus brevis, Lactobacillus acetotolerans, Lactobacillus sp., Lactococcus raffinolactis, Lactococcus lactis subsp. lactis and Streptococcus salivarius. The main species of acetic acid bacteria (AAB) identified in the mashita using PCR-DGGE method were Acetobacter aceti, Acetobacter lovaniensis, Acetobacter orientalis and Acetobacter pasteurianus. PCR-DGGE identification of yeasts showed that Brettanomyces custersianus, Candida silvae, Geotrichum sp., Issatchenkia occidentalis, Issatchenkia orientalis, Kluyveromyces marxianus, Saccharomyces cerevisiae, and Trichosporon asahii were main yeast species in mashita. A. lovaniensis, A. aceti, and I. orientalis were identified in all the six mashita samples analyzed using PCR-DGGE method. Other microbial species were only found in some samples. These results indicate that LAB and yeasts, as in similar fermentation products, but also AAB are main microbial groups involved in mashita fermentation.

Novel Isolates for Biological Detoxification of Lignocellulosic Hydrolysate

In this paper, two new strians, Issatchenkia occidentalis (Lj-3, CCTCC M 2006097) and Issatchenkia orienalis (S-7, CCTCC M 2006098), isolated from different environments on solid media, were used in the detoxification process of the hemicellulosic hydrolysate of sugarcane bagasse. High-pressure liquid chromatography elution curve of UV-absorption compounds represented by acetic acid, furfural, and guaiacol (toxic compounds found in the hemicellulosic hydrolysate) showed that several chromatographic peaks were evidently diminished for the case of detoxified hydrolysate with isolate strains compared to the high peaks resulted for no detoxified hydrolysate. It was clear that these inhibitors were degraded by the two new isolates during their cultivation process. Fermentation results for the biodetoxified hydrolysate showed an increase in xylitol productivity (Q (p)) by 1.97 and 1.95 times (2.03 and 2.01 g l(-1) h(-1)) and in xylitol yield (Y (p)) by 1.72 and 1.65 times (0.93 and 0.89 g xylitol per gram xylose) for hydrolysate treated with S-7 and Lj-3, respectively, in comparison with no detoxified hydrolysate (1.03 g l(-1) h(-1) and 0.54 g xylitol per gram xylose). This present work demonstrated the importance of Issatchenkia yeast in providing an effective biological detoxification approach to remove inhibitors and improve hydrolysate fermentability, leading to a high xylitol productivity and yield.

Sour rot-damaged grapes are sources of wine spoilage yeasts

Yeast species of sound and sour rot-damaged grapes were analysed during fermentation and grape ripening in the vineyard, using general and selective culture media. During 2003 and 2004 vintages, microvinifications were carried out with sound grapes to which different amounts of grapes with sour rot were added. The wine spoilage species Zygosaccharomyces bailii was only recovered during fermentations with sour rot, reaching 5.00 log CFU mL(-1) (2003) and 2.48 log CFU mL(-1) (2004) at the end of fermentation. The study of yeast populations during the sour rot ripening process (2005 vintage) showed that the veraison-damaged grapes always exhibited higher total yeast counts and a much greater diversity of species. From a total of 22 ascomycetous species, 17 were present only in damaged grapes. The most frequent species were Issatchenkia occidentalis and Zygoascus hellenicus. The spoilage species Z. bailii and Zygosaccharomyces bisporus were consistently isolated exclusively from damaged grapes. This work demonstrates that one of the most dangerous wine spoilage species, Z. bailii, is strongly associated with sour rot grapes and survives during fermentation with Saccharomyces cerevisiae. The use of selective media provides a more accurate characterization of grape contamination species.

Modelling the inhibition of sorbic and benzoic acids on a native yeast cocktail from table olives

The single and combined effects, in a synthetic medium at selected pH values, of sorbic and benzoic acids on a yeast cocktail ( Saccharomyces cerevisiae, Pichia anomala, Issatchenkia occidentalis, and Candida diddensiae, isolated from table olives) have been studied. Applying the checkerboard method the minimum inhibitory concentration (MIC) obtained for the respective individual preservatives (expressed as undissociated acid) were: sorbic acid, 5.94, 3.85 and 3.19 mM at pH of 4.5, 4.0, and 3.5, respectively; and benzoic acid, not detected (at total 20.5 mM), 10.40 and 6.83 mM, respectively, for the same pH levels. The estimated fractional inhibitory concentrations (FIC) indexes showed additive effects between inhibitors. Fractional area (fa), modelled by the (extended) Lambert and Lambert [2003. A model for the efficacy of combined inhibitors. J. Appl. Microbiol. 95, 734–743] equation (ELPM), also showed additives of both preservatives but different shapes in the dose–response curves; the individual MIC (as undissociated acid) deduced from this method were: 5.60, 3.31, and 3.26 mM for sorbic acid at pH of 4.5, 4.0, and 3.5, respectively; and 29.65 (extrapolated), 10.00, and 6.25 mM for benzoic acid at the same pH levels. Mixtures above the curves connecting the limits (MIC) at each pH were also inhibitory. There was agreement between MIC values from FIC and ELPM, although the last one provided further information on the inhibition behaviour. I. occidentalis was the most resistant yeast of the cocktail to sorbic and benzoic acids.