Adsorption of Zearalenone by Aureobasidium pullulans Autolyzed Biomass Preparation and Its Detoxification Properties in Cultures of Saccharomyces cerevisiae Yeast.

Different preventive strategies are needed to minimize the intake risks of mycotoxins, including zearalenone (ZEN). The aim of this study was to determine the ZEN adsorption ability of an autolyzed biomass preparation of polymorphic yeast Aureobasidium pullulans A.p.-3. The evaluation of the antitoxic properties of the preparation was also performed in relation to Saccharomyces cerevisiae yeast (ATCC 2366, ATCC 7090 and ATCC 9763) used as a model cell exposed to a toxic ZEN dose. The preparation at a dose of 5 mg/mL showed the adsorption of ZEN present in model systems at concentrations between 1 µg/mL to 100 µg/mL. The highest degree of adsorption was established for ZEN concentrations of 1 µg/mL and 5 µg/mL, becoming limited at higher doses of the toxin. Based on the Langmuir model of adsorption isotherms, the predicted maximum ZEN adsorption was approx. 190 µg/mL, regardless of pH. The growth of three strains of S. cerevisiae yeast cells in the medium with ZEN at concentrations within the range of 1.56 µg/mL-100 µg/mL was analyzed to determine the minimum inhibitory concentration. The growth of all tested strains was especially limited by high doses of ZEN, i.e., 50 and 100 µg/mL. The protective effect of the tested preparation was noted in relation to yeast cells exposed to toxic 100 µg/mL ZEN doses. The highest yeast cell growth (app. 36% percentage) was noted for a S. cerevisiae ATCC 9763 strain compared to the medium with ZEN but without preparation. More detailed tests determining the antitoxic mechanisms of the A. pullulans preparation are planned in the future, including cell culture bioassays and animal digestive tract models.

How do the carbon and nitrogen sources affect the synthesis of ß-(1,3/1,6)-glucan, its structure and the susceptibility of Candida utilis yeast cells to immunolabelling with ß-(1,3)-glucan monoclonal antibodies?

BACKGROUND: The need to limit antibiotic therapy due to the spreading resistance of pathogenic microorganisms to these medicinal substances stimulates research on new therapeutic agents, including the treatment and prevention of animal diseases. This is one of the goals of the European Green Deal and the Farm-To-Fork strategy. Yeast biomass with an appropriate composition and exposure of cell wall polysaccharides could constitute a functional feed additive in precision animal nutrition, naturally stimulating the immune system to fight infections. RESULTS: The results of the research carried out in this study showed that the composition of Candida utilis ATCC 9950 yeast biomass differed depending on growth medium, considering especially the content of ß-(1,3/1,6)-glucan, α-glucan, and trehalose. The highest ß-(1,3/1,6)-glucan content was observed after cultivation in deproteinated potato juice water (DPJW) as a nitrogen source and glycerol as a carbon source. Isolation of the polysaccharide from yeast biomass confirmed the highest yield of ß-(1,3/1,6)-glucan after cultivation in indicated medium. The differences in the susceptibility of ß-(1,3)-glucan localized in cells to interaction with specific ß-(1,3)-glucan antibody was noted depending on the culture conditions. The polymer in cells from the DPJW supplemented with glycerol and galactose were labelled with monoclonal antibodies with highest intensity, interestingly being less susceptible to such an interaction after cell multiplication in medium with glycerol as carbon source and yeast extract plus peptone as a nitrogen source. CONCLUSIONS: Obtained results confirmed differences in the structure of the ß-(1,3/1,6)-glucan polymers considering side-chain length and branching frequency, as well as in quantity of ß-(1,3)- and ß-(1,6)-chains, however, no visible relationship was observed between the structural characteristics of the isolated polymers and its susceptibility to immunolabeling in whole cells. Presumably, other outer surface components and molecules can mask, shield, protect, or hide epitopes from antibodies. ß-(1,3)-Glucan was more intensely recognized by monoclonal antibody in cells with lower trehalose and glycogen content. This suggests the need to cultivate yeast biomass under appropriate conditions to fulfil possible therapeutic functions. However, our in vitro findings should be confirmed in further studies using tissue or animal models.

Antimicrobial and prebiotic activity of mannoproteins isolated from conventional and nonconventional yeast species-the study on selected microorganisms.

Yeast mannoproteins are proposed as a paraprobiotics with antimicrobial and prebiotic properties. They can be used as biopreservatives in food and in diseases therapies. The knowledge about the specificity and/or capability of their influence on the growth of different microorganism is limited. The study determined the effect of mannoprotein preparations of Saccharomyces cerevisiae (S. cerevisiae) ATCC 7090 and nonconventional yeast origin [Metschnikowia reukaufii (M. reukaufii) WLP 4650 and Wickerhamomyces anomalus (W. anomalus) CCY 38-1-13] on the growth of selected bacteria of the genera: Lactobacilllus, Limosilatobacillus, Limosilatobacillus, Bifidobacterium, Staphylococcus, Enterococcus, Pseudomonas, Escherichia, Proteus and Salmonella. The degree of stimulation or growth inhibition of tested bacteria depended on the type and dose of the mannoprotein and the bacterial strain. The addition of the tested preparations in the entire range of applied concentrations had a positive effect especially on the growth of Lactobacillus arabinosus ATCC 8014 and Bifidobacterium animalis subsp. lactis B12. Mannoproteins isolated from S. cerevisiae limited the growth of the Escherichia coli (E. coli) ATCC 25922, Pseudomonas aureoginosa (P. aureoginosa) ATCC 27853, Proteus mirabilis ATCC 35659 and Salmonella Enteritidis ATCC 13076 to the greatest extent, while preparations of M. reukaufii and W. anomalus origin most effectively limited the growth of Staphylococcus aureus strains, E. coli and P. aureoginosa. The growth of Enterococcus faecalis was stimulated by the presence of all studied preparations in most of the concentrations used. Further research will determine how the purification process of studied mannoproteins or oligosaccharide fractions, its structure and composition influence on the growth of selected bacteria and what is the mechanism of its activity.

Recent advances on smart glycoconjugate vaccines in infections and cancer.

Vaccination is one of the greatest achievements in biomedical research preventing death and morbidity in many infectious diseases through the induction of pathogen-specific humoral and cellular immune responses. Currently, no effective vaccines are available for pathogens with a highly variable antigenic load, such as the human immunodeficiency virus or to induce cellular T-cell immunity in the fight against cancer. The recent SARS-CoV-2 outbreak has reinforced the relevance of designing smart therapeutic vaccine modalities to ensure public health. Indeed, academic and private companies have ongoing joint efforts to develop novel vaccine prototypes for this virus. Many pathogens are covered by a dense glycan-coat, which form an attractive target for vaccine development. Moreover, many tumor types are characterized by altered glycosylation profiles that are known as "tumor-associated carbohydrate antigens". Unfortunately, glycans do not provoke a vigorous immune response and generally serve as T-cell-independent antigens, not eliciting protective immunoglobulin G responses nor inducing immunological memory. A close and continuous crosstalk between glycochemists and glycoimmunologists is essential for the successful development of efficient immune modulators. It is clear that this is a key point for the discovery of novel approaches, which could significantly improve our understanding of the immune system. In this review, we discuss the latest advancements in development of vaccines against glycan epitopes to gain selective immune responses and to provide an overview on the role of different immunogenic constructs in improving glycovaccine efficacy.

Non-conventional yeasts for food and additives production in a circular economy perspective.

Yeast species have been spontaneously participating in food production for millennia, but the scope of applications was greatly expanded since their key role in beer and wine fermentations was clearly acknowledged. The workhorse for industry and scientific research has always been Saccharomyces cerevisiae. It occupies the largest share of the dynamic yeast market, that could further increase thanks to the better exploitation of other yeast species. Food-related 'non-conventional' yeasts (NCY) represent a treasure trove for bioprospecting, with their huge untapped potential related to a great diversity of metabolic capabilities linked to niche adaptations. They are at the crossroad of bioprocesses and biorefineries, characterized by low biosafety risk and produce food and additives, being also able to contribute to production of building blocks and energy recovered from the generated waste and by-products. Considering that the usual pattern for bioprocess development focuses on single strains or species, in this review we suggest that bioprospecting at the genus level could be very promising. Candida, Starmerella, Kluyveromyces and Lachancea were briefly reviewed as case studies, showing that a taxonomy- and genome-based rationale could open multiple possibilities to unlock the biotechnological potential of NCY bioresources.

Emerging glyco-based strategies to steer immune responses.

Glycan structures are common posttranslational modifications of proteins, which serve multiple important structural roles (for instance in protein folding), but also are crucial participants in cell-cell communications and in the regulation of immune responses. Through the interaction with glycan-binding receptors, glycans are able to affect the activation status of antigen-presenting cells, leading either to induction of pro-inflammatory responses or to suppression of immunity and instigation of immune tolerance. This unique feature of glycans has attracted the interest and spurred collaborations of glyco-chemists and glyco-immunologists to develop glycan-based tools as potential therapeutic approaches in the fight against diseases such as cancer and autoimmune conditions. In this review, we highlight emerging advances in this field, and in particular, we discuss on how glycan-modified conjugates or glycoengineered cells can be employed as targeting devices to direct tumor antigens to lectin receptors on antigen-presenting cells, like dendritic cells. In addition, we address how glycan-based nanoparticles can act as delivery platforms to enhance immune responses. Finally, we discuss some of the latest developments in glycan-based therapies, including chimeric antigen receptor (CAR)-T cells to achieve targeting of tumor-associated glycan-specific epitopes, as well as the use of glycan moieties to suppress ongoing immune responses, especially in the context of autoimmunity.

Comparison of simple and rapid cell wall disruption methods for improving lipid extraction from yeast cells.

The present study examined the effect of six disruption methods of the cell wall (acid hydrolysis, ultrasonication, osmotic shock, pasteurization, homogenization with zirconia balls, and freezing/defrosting) on the efficiency of lipid extraction from yeast cells and the composition of fatty acids. Acid hydrolysis and sonication led to a significant increase in lipid extraction from Cyberlindnera jadinii ATCC 9950 and Rhodotorula glutinis LOCKR13 yeast cells. The amount of lipids extracted in these conditions increased for C. jadinii from 12.46 (biomass not subjected to any pretreatment) to 20.37 and 19.53 g/100 gd.w. after the application of acid hydrolysis and sonication, respectively, and for R. glutinis strain from 13.95 to 21.20 and 17.22 g/100 gd.w., respectively, for the same methods. Initial sonication of biomass led to a significant reduction in the percentage of unsaturated fatty acids. The largest differences in fatty acid composition were found for the sample homogenized with zirconium balls. This process resulted in the degradation of both oleic acid and linolenic acid. The obtained results revealed that the method that significantly increases lipid extraction and does not change the composition of fatty acids is acid hydrolysis with hydrochloric acid. In addition, it is easy, cheap, does not require specialized equipment, and therefore can be implemented in any laboratory.

Chemical changes that occur in Jerusalem artichoke silage.

The effects of 10 and 20 days of fermentation followed by freeze-drying on the vitamin C and fatty acids contents, chemical conversions and overall chemical composition of Jerusalem artichoke were studied. Fermentation between the 10th and 20th days increased content of all saturated fatty acids and two of the four unsaturated fatty acids. The only fatty acid content that decreased was that of C18:1 cis 9 acid, which was suggested to be converted to other fatty acids. The experimental data, which were supported by energetical feasibility, suggested the reaction pathways of the mutual conversions of fatty acids and confirmed the decreased vitamin C content during fermentation. Discriminant modelling of the spectral data successfully distinguished the fresh, 10 days and 20 days fermented samples. The correlation of the spectral and reference data allowed to construct reference models for predicting the content of vitamin C and C18:1 cis 9 fatty acid.

Candida utilis ATCC 9950 Cell Walls and ß(1,3)/(1,6)-Glucan Preparations Produced Using Agro-Waste as a Mycotoxins Trap.

Mycotoxins are harmful contaminants of food and feed worldwide. Feed additives with the abilities to trap mycotoxins are considered substances which regulate toxin transfer from feed to tissue, reducing its absorption in animal digestive tract. Market analysis emphasizes growing interest of feed producers in mycotoxins binders obtained from yeast biomass. The aim of the study was to prescreen cell walls (CW) and ß(1,3)/(1,6)-glucan (ß-G) preparations isolated from Candida utilis ATCC 9950 cultivated on waste potato juice water with glycerol as adsorbents for aflatoxin B1 (AFB1), zearalenone (ZEN), ochratoxin A (OTA), deoxynivalenol (DON), nivalenol (NIV), T-2 toxin (T-2) and fumonisin B1 (FB1). The adsorption was studied in single concentration tests at pH 3.0 and 6.0 in the presence of 1% of the adsorbent and 500 ng/mL of individual toxin. Evaluated CW and ß-G preparations had the potential to bind ZEN, OTA and AFB1 rather than DON, NIV, T-2 toxin and FB1. The highest percentage of adsorption (about 83%), adsorption capacity (approx. 41 µg/ g preparation) and distribution coefficient (458.7mL/g) was found for zearalenone when CW preparation was used under acidic conditions. Higher protein content in CW and smaller particles sizes of the formulation could influence more efficient binding of ZEN, OTA, DON and T-2 toxin at appropriate pH compared to purified ß-G. Obtained results show the possibility to transform the waste potato juice water into valuable Candida utilis ATCC 9950 preparation with mycotoxins adsorption properties. Further research is important to improve the binding capacity of studied preparations by increasing the active surface of adsorption.

Effect of selenium on growth and antioxidative system of yeast cells.

Selenium exhibits health-promoting properties in humans and animals. Therefore, the development of selenium-enriched dietary supplements has been growing worldwide. However, it may also exhibit toxicity at higher concentrations, causing increased oxidative stress. Different species of yeasts may exhibit different tolerances toward selenium. Therefore, in this study, we aimed to determine the effect of selenium on growth and on the antioxidative system in Candida utilis ATCC 9950 and Saccharomyces cerevisiae ATCC MYA-2200 yeast cells. The results of this study have demonstrated that high doses of selenium causes oxidative stress in yeasts, thereby increasing the process of lipid peroxidation. In addition, we obtained an increased level of GSSG from aqueous solutions of yeast biomass grown with selenium supplementation (40-60 mg/L). Increased levels of selenium in aqueous solutions resulted in an increase in the activity of antioxidant enzymes, including glutathione peroxidase and glutathione reductase. These results should encourage future research on the possibility of a thorough understanding of antioxidant system functioning in yeast cells.

Correction to: Effect of Selenium on Lipid and Amino Acid Metabolism in Yeast Cells.

The authors forgot to include the following information in Materials and Methods.

Effect of Selenium on Lipid and Amino Acid Metabolism in Yeast Cells.

This article discusses the effect of selenium in aqueous solutions on aspects of lipid and amino acid metabolism in the cell biomass of Saccharomyces cerevisiae MYA-2200 and Candida utilis ATCC 9950 yeasts. The yeast biomass was obtained by using waste products (potato wastewater and glycerol). Selenium, at a dose of 20 mg/L of aqueous solution, affected the differentiation of cellular morphology. Yeast enriched with selenium was characterized by a large functional diversity in terms of protein and amino acid content. The protein content in the biomass of S. cerevisiae enriched with selenium (42.6%) decreased slightly as compared to that in the control sample without additional selenium supplementation (48.4%). Moreover, yeasts of both strains enriched with selenium contained a large amount of glutamic acid, aspartic acid, lysine, and leucine. Analysis of fatty acid profiles in S. cerevisiae yeast supplemented with selenium showed an increase in the unsaturated fatty acid content (e.g., C18:1). The presence of margaric acid (C17:0) and hexadecanoic acid (C17:1) was found in the C. utilis biomass enriched with selenium, in contrast to that of S. cerevisiae. These results indicate that selenium may induce lipid peroxidation, which consequently affects the loss of integrity of the cytoplasmic membrane. Yeast enriched with selenium with optimal amino acid and lipid composition can be used to prepare a novel formula of dietary supplements, which can be applied directly to various diets for both humans and animals.

The scale-up cultivation of Candida utilis in waste potato juice water with glycerol affects biomass and ß(1,3)/(1,6)-glucan characteristic and yield.

New ideas on production of yeast origin ß-glucan preparations for industrial application are attracting interest considering market development of that high-value functional polysaccharide. Sellecting an efficient yeast producer and designing culture conditions are a prerequisite for obtaining high yield of ß-glucan. The aim of this study was to describe at the first time the influence of the mode of cultivation (shake-flasks and batch fermentation) and time of culture on characteristic and yield of biomass and ß(1,3)/(1,6)-glucan preparations of Candida utilis ATCC 9950 after cultivation in medium based on waste potato juice water supplemented with 10% of glycerol. After shake-flask culture, the biomass was characterized by higher protein content (app. 26.5%) compared to 19% after batch fermentation while the cultivation on a biofermentor scale promoted polysaccharides biosynthesis. The highest output of purified ß(1,3)/(1,6)-glucan preparation (5.3 gd.w./L), containing app. 85% of that polysaccharide, was found after 48 h cultivation in biofermentor. Batch fermentation promoted biosynthesis of alkali-insoluble ß(1,3)/(1,6)-glucan fraction, decreasing the content of ß(1,6)-glucan. The yield of ß(1,3)/(1,6)-glucan synthesis was 0.063 (g/g glycerol), while the productivity of that polysaccharide reached 0.094 (g/L/h). Longer batch fermentation (72 h) resulted in reduction of production efficiency of ß-glucan preparation under studied conditions. The results of the study provide a new efficient biotechnological solution to produce high-value ß-glucan preparations of C. utilis origin based on valorization of agro-waste potato juice water with glycerol.

Modification of the cell wall structure of Saccharomyces cerevisiae strains during cultivation on waste potato juice water and glycerol towards biosynthesis of functional polysaccharides.

Changes in cell wall structure of four strains of Sacccharomyces cerevisiae species (brewer's, baker's and probiotic yeast) after culturing on deproteinated potato juice water (DPJW) with diverse addition of glycerol and different pH were investigated. It allowed to select conditions intensifying biosynthesis of ß(1,3)/(1,6)-glucan and mannoproteins of cell walls of tested strains. Yeast cell wall structural polysaccharides show biological activity and technological usability in food industry but also decide about therapeutic properties of yeast biomass. The highest increase in the thickness of walls (by about 100%) and ß-glucan layer (by about 120%) was stated after cultivation of S. cerevisiae R9 brewer's yeast in DPJW supplemented with 5 and 10% (w/v) of glycerol and pH 7.0 while S. cerevisiae var. boulardi PAN yeast synthesized by ab. 70% thicker ß-glucan layer when the pH of growth medium was equal to 5.0. The cells of brewer's yeast (S. cerevisiae R9), probiotic (S. cerevisiae CNCM 1-745) and baker's (S. cerevisiae 102) intensified the ratio of mannoproteins in the structure of cell walls cultivated in mediums supplemented with above 15% of glycerol what point out the protective action of glycoprotein's under osmotic stress conditions. The study confirms at the first time the possibility of using agro-industrial waste in biosynthesis of functional polysaccharides of S. cerevisiae cell wall. It could be an new advantage in production of yeast biomass with therapeutic properties or ß-glucan preparation as a novel food ingredient.

Research on the ability of propionic acid and vitamin B12 biosynthesis by Propionibacterium freudenreichii strain T82.

The purpose of this study was to determine the potential for biosynthesis of propionic acid and vitamin B12 by Propionibacterium freudenreichii T82 in a medium containing various sources of carbon (glucose, fructose, and saccharose). These sugars are present in apple pomaces, which are the waste from the production of apple juice. Using statistical analysis design of experiments (DoE), the results allowed us to determine which sugars (carbon sources) exert the most beneficial influence on the biosynthesis of propionic acid and cobalamin. The highest production of propionic acid by the tested bacterial strain was obtained in a medium in which glucose accounted for at least 50% of the available carbon sources. Depending on the culture medium, the concentration of this metabolite ranged from 23 to 40 g/L. P. freudenreichii T82 produced the smallest amount of acid in medium in which the dominant nutrient source was saccharose. The results obtained indicated an inverse relationship between the amount of acid produced by the bacteria and vitamin B12 biosynthesis. Because of the high efficiency of propionic acid biosynthesis by P. freudenreichii T82, the prospect of using this strain to obtain propionate with the simultaneous disposal of waste materials (such as apple pomaces) which contain glucose and/or fructose is very promising.

Effect of initial pH of medium with potato wastewater and glycerol on protein, lipid and carotenoid biosynthesis by Rhodotorula glutinis

Background: Rhodotorula glutinis is capable of synthesizing numerous valuable metabolites with extensive potential industrial usage. This paper reports the effect of initial culture medium pH on growth and protein, lipid, and carotenoid biosynthesis by R. glutinis. Results: The highest biomass yield was obtained in media with pH 4.0­7.0, and the value after 72 h was 17.2­19.4 gd.w./L. An initial pH of the medium in the range of 4.0­7.0 has no significant effect on the protein (38.5­41.3 g/100 gd.w.), lipid (10.2­12.7 g/100 gd.w.), or carotenoid (191.7­202.9 µg/gd.w.) content in the biomass or on the profile of synthesized fatty acids and carotenoids. The whole pool of fatty acids was dominated by oleic (48.1­53.4%), linoleic (21.4­25.1%), and palmitic acids (13.0­15.8%). In these conditions, the yeast mainly synthesized torulene (43.5­47.7%) and ß-carotene (34.7­38.6%), whereas the contribution of torularhodin was only 12.1­16.8%. Cultivation in medium with initial pH 3.0 resulted in a reduction in growth (13.0 gd.w./L) and total carotenoid (115.8 µg/gd.w.), linoleic acid (11.5%), and torularhodin (4.5%) biosynthesis. Conclusion: The different values of initial pH of the culture medium with glycerol and deproteinized potato wastewater had a significant effect on the growth and protein, lipid, and carotenoid biosynthesis by R. glutinis.

Utilization of a waste glycerol fraction using and reusing immobilized Gluconobacter oxydans ATCC 621 cell extract

Background: Depletion of petroleum resources has enforced the search for alternative sources of renewable energy. Introduction of biofuels into the market was expected to become a solution to this disadvantageous situation. Attempts to cover fuel demand have, however, caused another severe problem­the waste glycerol generated during biodiesel production at a concentration of approximately 10% w/w. This, in turn, prompted a global search for effective methods of valorization of the waste fraction of glycerol. Results: Utilization of the waste fraction at 48 h with an initial glycerol concentration of 30 g·L-1 and proceeding with 62% efficiency enabled the production of 9 g·L-1 dihydroxyacetone at 50% substrate consumption. The re-use of the immobilized biocatalyst resulted in a similar concentration of dihydroxyacetone (8.7 g·L-1) in two-fold shorter time, with an efficiency of 85% and lower substrate consumption (35%). Conclusions: The method proposed in this work is based on the conversion of waste glycerol to dihydroxyacetone in a reaction catalyzed by immobilized Gluconobacter oxydans cell extract with glycerol dehydrogenase activity, and it could be an effective way to convert waste glycerol into a valuable product.

Effect of Magnesium Acetate on the Antimold Activity of Lactobacillus.

The antimold activity of lactic acid bacteria (LAB) is used in food biopreservation. The aim of this study was to evaluate the effect of magnesium acetate added to de Man Rogosa Sharpe (MRS) medium on the antimold activity of three LAB strains ( Lactobacillus plantarum , Lactobacillus brevis , and Lactobacillus fermentum ) against molds contaminating food ( Aspergillus oryzae , Aspergillus niger , Penicillium chrysogenum , Fusarium avenaceum , and Rhizopus arrhizus ) and their ability to produce organic acids (acetic acid, lactic acid, and phenyllactic acid). The antimold activity of LAB strains was evaluated using the overlay method, and the concentration of the organic acids was determined with the gas chromatography technique. Changes in viable cell counts and the pH of LAB culture also were monitored over a 48-h period. The results show that the growth inhibition of all the molds (except R. arrhizus ) was higher in LAB strain cultures on MRS with magnesium acetate agar than on MRS agar, and inhibition increased over the 48 h. Magnesium acetate added to MRS broth stimulated the production of acetic acid by all LAB strains in the first 8 h and slightly stimulated the production of lactic acid by L. plantarum during the first 24 h. No adverse effect of magnesium acetate on growth of LAB strains was noted. The results confirm that magnesium acetate enhances the antimold activity of LAB strains.

The Effect of Pullulan on the Growth and Acidifying Activity of Selected Stool Microflora of Human.

BACKGROUND: Pullulan is a microbial polysaccharide of low energy value, which can component of low-calorie foods and in dietary snacks for diabetics. The objective of the study was to determine the effect of pullulan on the growth and fermentation activity of selected human intestinal bacteria. METHODS: Commercial pullulan purchased from Focubase (China) of a molecular weight of 100,000 Da constituted as experimental material. Food grade pullulan 99% purity. Two control media were prepared: the first standard RCM composed of (g/100 ml): 0.5 glucose, 0.1 soluble starch, 1.0 peptone, 1.0 meat extract, 0.3 yeast extract, 0.3 sodium acetate, 0.05 cysteine hydrochloride, 0.5 NaCl, pH 6.8; and the second modified RCM, wherein the soluble starch was replaced by increased glucose concentration to 2.0% (RCM+G). Experimental medium was the modified RCM medium, wherein the soluble starch and glucose were replaced by pullulan at a concentration of 2.0% (RCM+P). Stool suspensions were prepared from fresh stool samples (1 g) in peptone water (9 g), which were previously homogenized. Then, suspensions at a volume of 300 µl were transferred to the media (RCM, RCM+G, and RCM+P). After mixing, flasks were placed in anaerobic tubes with AnaeroGenTM 2.5 l sachets. Incubation of samples was carried out at 37°C for 48 h. RESULTS: The number of Bifidobacterium, Lactobacillus, and Escherichia coli bacteria, as well as pH and total acidity of the culture during 0, 24, and 48 h were measured. It was found that the numbers of bacteria of the Bifidobacterium and Lactobacillus genus in medium with pullulan were one logarithmic cycle lower in comparison to their numbers in the control media. Higher total acidity (1.48 g/100 ml) of pullulan culture in comparison to the control media was obtained (1.10 and 0.60 g/100 ml), and lower pH values than RCM medium, particularly 4.15 and 4.70, respectively. Pullulan exhibited selective effect on the natural microflora of the colon. Increase in the fermentation activity of bacteria in medium with pullulan favorably influenced modification of the composition of gut microbiota. CONCLUSION: In summary, pullulan exhibited a selective effect on the natural microflora of the infants' colon. Although no stimulating effect of pullulan on the growth of Bifidobacterium and Lactobacillus was observed, their increased acidifying activity, which probably was the cause of reduction in the number of E. coli bacteria, was confirmed.

The exopolysaccharides biosynthesis by Candida yeast depends on carbon sources

Background: The exopolysaccharides (EPS) produced by yeast exhibit physico-chemical and rheological properties, which are useful in the production of food and in the cosmetic and pharmaceutical industries as well. The effect was investigated of selected carbon sources on the biosynthesis of EPS by Candida famata and Candida guilliermondii strains originally isolated from kefirs. Results: The biomass yields were dependent on carbon source (sucrose, maltose, lactose, glycerol, sorbitol) and ranged from 4.13 to 7.15 g/L. The highest biomass yield was reported for C. guilliermondii after cultivation on maltose. The maximum specific productivity of EPS during cultivation on maltose was 0.505 and 0.321 for C. guilliermondii and C. famata, respectively. The highest EPS yield was found for C. guilliermondii strain. The EPS produced under these conditions contained 65.4% and 61.5% carbohydrates, respectively. The specific growth rate (µ) of C. famata in medium containing EPS as a sole carbon source was 0.0068 h-1 and 0.0138 h-1 for C. guilliermondii strain. Conclusions: The most preferred carbon source in the synthesis of EPS for both Candida strains was maltose, wherein C. guilliermondii strain showed the higher yield of EPS biosynthesis. The carbon source affected the chemical composition of the resulting EPS and the contribution of carbohydrate in the precipitated preparation of polymers was higher during supplementation of maltose as compared to sucrose. It was also found that the EPS can be a source of carbon for the producing strains.