Effects of acidification by traditional Jiaozi starter and neutralization with alkali (Na2CO3) on whole wheat dough properties.

BACKGROUND: Whole wheat steamed bread has been recommended for its potential nutritional benefits to human health. Given the positive role of both organic acid and alkali in improving dough development and product quality, the present study investigated the effects of neutralization by addition of alkali (Na2CO3) after dough acidification with traditional Jiaozi starter on the properties of whole wheat dough. RESULTS: The population of yeast and lactic acid bacteria and the acidification level of the dough increased significantly after fermentation with Jiaozi. Incorporation of alkali greatly improved the leavening capacity of the remixed dough and the quality of steamed bread. Jiaozi fermentation and alkali addition changed the water distribution patterns (T2) and affected the secondary structures of gluten protein, starch crystallinity and pasting properties. The storage modulus (G') of the dough increased significantly with the alkali addition, which could be attributed to the promoted cross-linking of the gluten structure and the altered hydration state of the macromolecules. CONCLUSION: The results of the present study indicate that a combination of Jiaozi fermentation and alkali addition could improve the technological properties of whole wheat dough and the quality of steamed bread. The results will help us to further explore the potential application of moderate acidification and alkali addition in the production of leavened whole wheat products. © 2024 Society of Chemical Industry.

Nile red-based lipid fluorometry protocol and its use for statistical optimization of lipids in oleaginous yeasts.

As lipogenic yeasts are becoming increasingly harnessed as biofactories of oleochemicals, the availability of efficient protocols for the determination and optimization of lipid titers in these organisms is necessary. In this study, we optimized a quick, reliable, and high-throughput Nile red-based lipid fluorometry protocol adapted for oleaginous yeasts and validated it using different approaches, the most important of which is using gas chromatography coupled to flame ionization detection and mass spectrometry. This protocol was applied in the optimization of the concentrations of ammonium chloride and glycerol for attaining highest lipid titers in Rhodotorula toruloides NRRL Y-6987 and Yarrowia lipolytica W29 using response surface central composite design (CCD). Results of this optimization showed that the optimal concentration of ammonium chloride and glycerol is 4 and 123 g/L achieving a C/N ratio of 57 for R. toruloides, whereas for Y. lipolytica, concentrations are 4 and 139 g/L with a C/N ratio of 61 for Y. lipolytica. Outside the C/N of 33 to 74 and 45 to 75, respectively, for R. toruloides and Y. lipolytica, lipid productions decrease by more than 10%. The developed regression models and response surface plots show the importance of the careful selection of C/N ratio to attain maximal lipid production. KEY POINTS: • Nile red (NR)-based lipid fluorometry is efficient, rapid, cheap, high-throughput. • NR-based lipid fluorometry can be well used for large-scale experiments like DoE. • Optimal molar C/N ratio for maximum lipid production in lipogenic yeasts is ~60.

Michler's hydrol blue elucidates structural differences in prion strains.

Yeast prions provide self-templating protein-based mechanisms of inheritance whose conformational changes lead to the acquisition of diverse new phenotypes. The best studied of these is the prion domain (NM) of Sup35, which forms an amyloid that can adopt several distinct conformations (strains) that confer distinct phenotypes when introduced into cells that do not carry the prion. Classic dyes, such as thioflavin T and Congo red, exhibit large increases in fluorescence when bound to amyloids, but these dyes are not sensitive to local structural differences that distinguish amyloid strains. Here we describe the use of Michler's hydrol blue (MHB) to investigate fibrils formed by the weak and strong prion fibrils of Sup35NM and find that MHB differentiates between these two polymorphs. Quantum mechanical time-dependent density functional theory (TDDFT) calculations indicate that the fluorescence properties of amyloid-bound MHB can be correlated to the change of binding site polarity and that a tyrosine to phenylalanine substitution at a binding site could be detected. Through the use of site-specific mutants, we demonstrate that MHB is a site-specific environmentally sensitive probe that can provide structural details about amyloid fibrils and their polymorphs.

Identification of yeasts in fermented foods and beverages using MALDI-TOF MS.

Yeasts are an important group of microorganisms and contribute to the fermentation of a broad range of foods and beverages spontaneously or as a starter culture. Rapid and reliable microbial species identification is essential to evaluate biodiversity in fermented foods and beverages. Nowadays, high-throughput omics technologies and bioinformatics tools produce large-scale molecular-level data in many fields. These omics technologies generate data at different expression levels and are used to identify microorganisms. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a powerful analytical technique in proteomic technology. It is a tool used to analyze the peptides or proteins of microorganisms for identification. MALDI-TOF MS has been used for the taxonomic identification of microorganisms as a fast, high-throughput, and cost-effective method. This review briefly discussed the application of MALDI-TOF MS in identifying yeasts in fermented foods and beverages.

Single-nucleotide control of tRNA folding cooperativity under near-cellular conditions.

RNA folding is often studied by renaturing full-length RNA in vitro and tracking folding transitions. However, the intracellular transcript folds as it emerges from the RNA polymerase. Here, we investigate the folding pathways and stability of numerous late-transcriptional intermediates of yeast and Escherichia coli transfer RNAs (tRNAs). Transfer RNA is a highly regulated functional RNA that undergoes multiple steps of posttranscriptional processing and is found in very different lengths during its lifetime in the cell. The precursor transcript is extended on both the 5' and 3' ends of the cloverleaf core, and these extensions get trimmed before addition of the 3'-CCA and aminoacylation. We studied the thermodynamics and structures of the precursor tRNA and of late-transcriptional intermediates of the cloverleaf structure. We examined RNA folding at both the secondary and tertiary structural levels using multiple biochemical and biophysical approaches. Our findings suggest that perhaps nature has selected for a single-base addition to control folding to the functional 3D structure. In near-cellular conditions, yeast tRNAPhe and E. coli tRNAAla transcripts fold in a single, cooperative transition only when nearly all of the nucleotides in the cloverleaf are transcribed by indirectly enhancing folding cooperativity. Furthermore, native extensions on the 5' and 3' ends do not interfere with cooperative core folding. This highly controlled cooperative folding has implications for recognition of tRNA by processing and modification enzymes and quality control of tRNA in cells.

Study on the Incorporation of Oat and Yeast ß-Glucan into Shortbread Biscuits as a Basis for Designing Healthier and High Quality Food Products.

According to international health and food organizations and authorities, people should limit fat intake since fat is the most caloric component of food and it is often a source of unsafe saturated fatty acids (FA) and trans isomers. The greatest health benefits come from replacing shorts with dietary fiber molecules. The aim of the study was to determine the possibility of reducing shortening content, which has an undesirable profile of FA, by addition of ß-glucan molecules in shortbread biscuits. The effect of oat and yeast ß-glucan supplementation on physical and sensory quality of products with reduced fat content (max 15%) were studied. It was shown that the substitution of shortening by ß-glucan in shortbread biscuits is possible to a limited extent. Reduction in product energy value (up to 36 kcal/100 g) and content of undesirable FA (maximum 2.1 g/100 g) and increased of ß-glucan content, regardless of the type, caused deterioration of biscuits quality and affected changes during storage. The substitution of shortening by ß-glucan in food is a good way to improve nutritional value by increasing the amount of dietary fiber molecules, reducing calories, and amount of SFA in diets.

Induction of amylase and protease as antibiofilm agents by starch, casein, and yeast extract in Arthrobacter sp. CW01.

BACKGROUND: In unfavourable environment, such as nutrient limitation, some bacteria encased themselves into a three dimensional polymer matrix called biofilm. The majority of microbial infections in human are biofilm related, including chronic lung, wound, and ear infections. The matrix of biofilm which consists of extracellular polymeric substances (EPS) causes bacterial colonization on medical implanted device in patients, such as catheter and lead to patient's death. Biofilm infections are harder to treat due to increasing antibiotic resistance compared to planktonic microbial cells and escalating the antibiotic concentration may result into in vivo toxicity for the patients. Special compounds which are non-microbicidal that could inhibit or destroy biofilm formation are called antibiofilm compounds, for example enzymes, anti-quorum sensing, and anti-adhesins. Arthrobacter sp. CW01 produced antibiofilm compound known as amylase. This time our preliminary study proved that the antibiofilm compound was not only amylase, but also protease. Therefore, this research aimed to optimize the production of antibiofilm agents using amylase and protease inducing media. The five types of production media used in this research were brain heart infusion (BHI) (Oxoid), BHI with starch (BHIS), casein with starch (CS), yeast extract with starch (YS), and casein-yeast extract with starch (CYS). Biofilm eradication and inhibition activities were assayed against Pseudomonas aeruginosa (ATCC 27,853) and Staphylococcus aureus (ATCC 25,923). RESULTS: The results showed that different production media influenced the antibiofilm activity. Addition of starch, casein and yeast extract increased the production of amylase and protease significantly. Higher amylase activity would gradually increase the antibiofilm activity until it reached the certain optimum point. It was shown that crude extracts which contained amylase only (BHI, BHIS and YS) had the optimum eradication activity against P. aeruginosa and S. aureus biofilm around 60-70 %. Meanwhile, CS and CYS crude extracts which contained both amylase and protease increased the biofilm eradication activity against both pathogens, which were around 70-90 %. CONCLUSIONS: It was concluded that the combination of amylase and protease was more effective as antibiofilm agents against P. aeruginosa and S. aureus rather than amylase only.

Yeast carotenoids: production and activity as antimicrobial biomolecule.

Carotenoids are a large group of organic, pigmented, isoprenoid-type compounds that play biological activities in plants and microorganisms (yeasts, bacteria, and microalgae). Literature reported it as vitamin A precursors and antioxidant activity. Carotenoids also can act as antimicrobial agents and few reports showed quantitative measurements of Minimal Inhibitory Concentrations against different pathogens. In this sense, some carotenoids were added to medical-surgical materials. The demand for scale-up of different naturally obtained carotenoids has increased due to the concern about the detrimental health effects caused by synthetic molecules and antimicrobial resistance. In this review, we reported the variability in pigment production and culture conditions, extraction methods used in laboratory, and we discussed the antimicrobial activity carried out by these molecules and the promising acting as new molecules to be scaled-up to industry.

Multicenter evaluation of the VITEK MS matrix-assisted laser desorption/ionization-time of flight mass spectrometry system for identification of bacteria, including Brucella, and yeasts.

The use of matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry has proven to be rapid and accurate for the majority of clinical isolates. Some gaps remain concerning rare, emerging, or highly pathogenic species, showing the need to continuously expand the databases. In this multicenter study, we evaluated the accuracy of the VITEK MS v3.2 database in identifying 1172 unique isolates compared to identification by DNA sequence analysis. A total of 93.6% of the isolates were identified to species or group/complex level. A remaining 5.2% of the isolates were identified to the genus level. Forty tests gave a result of no identification (0.9%) and 12 tests (0.3%) gave a discordant identification compared to the reference identification. VITEK MS is also the first MALDI-TOF MS system that is able to delineate the four members of the Acinetobacter baumannii complex at species level without any specific protocol or special analysis method. These findings demonstrate that the VITEK MS v3.2 database is highly accurate for the identification of bacteria and fungi encountered in the clinical laboratory as well as emerging species like Candida auris and the highly pathogenic Brucella species.

Human gut Bacteroidetes can utilize yeast mannan through a selfish mechanism.

Yeasts, which have been a component of the human diet for at least 7,000 years, possess an elaborate cell wall α-mannan. The influence of yeast mannan on the ecology of the human microbiota is unknown. Here we show that yeast α-mannan is a viable food source for the Gram-negative bacterium Bacteroides thetaiotaomicron, a dominant member of the microbiota. Detailed biochemical analysis and targeted gene disruption studies support a model whereby limited cleavage of α-mannan on the surface generates large oligosaccharides that are subsequently depolymerized to mannose by the action of periplasmic enzymes. Co-culturing studies showed that metabolism of yeast mannan by B. thetaiotaomicron presents a 'selfish' model for the catabolism of this difficult to breakdown polysaccharide. Genomic comparison with B. thetaiotaomicron in conjunction with cell culture studies show that a cohort of highly successful members of the microbiota has evolved to consume sterically-restricted yeast glycans, an adaptation that may reflect the incorporation of eukaryotic microorganisms into the human diet.

The coming age of complete, accurate, and ubiquitous proteomes.

High-resolution mass spectrometry (MS)-based proteomics has progressed tremendously over the years. For model organisms like yeast, we can now quantify complete proteomes in just a few hours. Developments discussed in this Perspective will soon enable complete proteome analysis of mammalian cells, as well, with profound impact on biology and biomedicine.

Enhancement of LacI binding in vivo.

Transcription factors (TFs) bind to specific sequences in DNA to regulate transcription. Despite extensive measurements of TFs' dissociation constant (Kd) in vitro, their apparent Kdin vivo are usually unknown. LacI, a bacterial TF, is often used to artificially recruit proteins onto eukaryotic genomes. As LacI binds tightly to its recognition site (LacO) in vitro with a Kd about 10 picomolar (pM), it is often assumed that LacI also has high affinity to LacO in vivo. In this work, we measured LacI binding in living yeast cells using a fluorescent repressor operator system and found an apparent Kd of ∼0.6 µM, four orders of magnitude higher than that in vitro. By genetically altering (i) GFP-LacI structure, (ii) GFP-LacI stability, (iii) chromosome accessibility and (iv) LacO sequence, we reduced the apparent Kd to <10 nM. It turns out that the GFP tagging location and the fusion protein stability have a large effect on LacI binding, but surprisingly, chromosome accessibility only plays a mild role. These findings contribute to our quantitative understanding of the features that affect the apparent Kd of TF in cells. They also provide guidance for future design of more specific chromosomal recruitment through high-affinity TFs.

Improvement of glutathione production by a metabolically engineered Yarrowia lipolytica strain using a small-scale optimization approach.

OBJECTIVE: In this study, we aimed to maximize glutathione (GSH) production by a metabolically engineered Yarrowia lipolytica strain using a small-scale optimization approach. RESULTS: A three levels four factorial Box-Behnken Design was used to assess the effect of pH, inulin extract, yeast extract and ammonium sulfate concentrations on cell growth and to generate a mathematical model which predict optimal conditions to maximize biomass production and thus GSH titer. The obtained results revealed that only yeast and inulin extract concentrations significantly affect biomass production. Based on the generated model, a medium composed of 10 g/L of yeast extract and 10 g/L of inulin extract from Jerusalem artichoke was used to conduct batch cultures in 2 L bioreactor. After 48 h of culture, the biomass and the glutathione titer increased by 55% (5.8 gDCW/L) and 61% (1011.4 mg/L), respectively, as compared to non-optimized conditions. CONCLUSION: From the obtained results, it could be observed that the model established from small scale culture (i.e. 2 mL) is able to predict performance at larger scale (i.e. 2 L bioreactor, two orders of magnitude scale-up). Moreover, the results highlight the ability of the optimized process to ensure high titer of glutathione using a low-cost carbon source.

Application of MALDI-TOF analysis to reveal diversity and dynamics of winemaking yeast species in wild-fermented, organically produced, New Zealand Pinot Noir wine.

Rapid yeast identification is of particular importance in monitoring wine fermentation and assessing strain application in winemaking. We used MALDI-TOF MS analysis supported by 26 S rRNA gene sequence analysis and Saccharomyces-specific PCR testing to differentiate reference and field strains recovered from organic wine production facilities in Waipara, New Zealand, in which Pinot Noir wine was produced by spontaneous fermentations in the vineyard and in the winery. Strains were isolated from each of four key stages of each ferment to evaluate changes in taxonomic diversity. MALDI-TOF MS analysis was confirmed as an excellent yeast identification method, with even closely related Saccharomyces species readily distinguished. A total of 13 indigenous species belonging to eight genera were identified from Pinot Noir ferments, with taxonomic diversity generally reducing as fermentation progressed. However, differences between the taxa recovered were observed between the vineyard and winery ferments, despite the grapes used being from the same batch. Furthermore, some consistent proteomic differences between strains of S. cerevisiae, Hanseniasporum uvarum, Candida californica, Pichia membranifaciens and Starmerella bacillaris correlated with the different fermentation systems used. The high speed, low cost, taxonomic resolution and ability to characterise subtle changes in phenotype that may result from variations in environmental conditions makes MALDI-TOF analysis an attractive tool for further and wider applications in the wine industry. Such applications may include monitoring wine fermentation to actively support the consistency of high-quality wine products, and potentially for the development of such products too.

Screening for heat-resistant reference yeast isolate in orange juice.

This study details a screening process for yeast species that may be used as reference microorganisms for mild thermal processing of orange juice. In the initial step, 17 different strains of spoilage yeasts with similar initial populations (6.0-7.0 log CFU/mL) and growth stage (middle stationary phase) were subjected to equal heating process (55 °C, 5 min) in Yeast Peptone Glucose Broth (pH 6.06). The change in populations observed ranged from 3.33 log CFU/mL (Pichia fermentans BFE-38) to 6.53 log CFU/mL (Torulaspora delbrueckii BFE-37). In the second step of the screening, 6 of the most resistant strains were further challenged in an orange juice suspending medium (pH 3.88, 10.02 °Brix, 0.82% citric acid) at different heating temperatures (50, 53, 55, 57, and 60 °C). The decimal reduction times (DT values) and thermal resistant constants (z values) were determined. Results showed that all tested yeasts exhibited first-order, log-linear inactivation behavior (R2 0.90-0.99). As expected, significant (P < 0.05) reduction in the DT values were observed with increasing temperature. P. fermentans BFE-38 exhibited the greatest Dvalues at 50-55 °C. However, the test isolate with the greatest z-value was found to be P. anomala (BIOTECH 2205).

One-step synthesis of N, S-doped carbon dots with orange emission and their application in tetracycline antibiotics, quercetin sensing, and cell imaging.

Water soluble N, S-doped carbon dots (N, S-CDs) with orange emission were synthesized from basic fuchsin and sulfosalicylic acid by the typical hydrothermal route. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for sensitive determination of tetracycline antibiotics (for example, chlortetracycline (CTC)) and quercetin. The proposed sensor was utilized to realize the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm) with satisfactory recoveries and relative standard deviations (RSD). The linear range and detection limit (LOD) of CTC is 1.24-165 µM and 32.36 nM, respectively. For quercetin, the linear ranges are 0.98-34 µM and 34-165 µΜ, and the LOD is 6.87 nM (3σ/m). By virtue of the good biocompatibility and long-wavelength emission, N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bio-imaging and sensing. In this paper, N, S-doped carbon dots (N, S-CDs) with orange emission (λem = 605 nm) were synthesized from basic fuchsin and sulfosalicylic acid. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for the sensing of tetracycline antibiotics (for example: chlortetracycline (CTC)) and quercetin. The sensor has been successfully applied to the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm). The linear range and detection limit (LOD) of CTC is 1.24-165 µM and 32.36 nM respectively. For quercetin, the linear ranges are 0.98-34 µM and 34-165 µΜ, and the LOD is 6.87 nM (3σ/m). In addition, due to the characteristics of good biocompatibility and long-wavelength emission, the N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bioimaging and sensing.

The Role of Bioactive Phenolic Compounds on the Impact of Beer on Health.

This review reports recent knowledge on the role of ingredients (barley, hop and yeasts), including genetic factors, on the final yield of phenolic compounds in beer, and how these molecules generally affect resulting beer attributes, focusing mainly on new attempts at the enrichment of beer phenols, with fruits or cereals other than barley. An entire section is dedicated to health-related effects, analyzing the degree up to which studies, investigating phenols-related health effects of beer, have appropriately considered the contribution of alcohol (pure or spirits) intake. For such purpose, we searched Scopus.com for any kind of experimental model (in vitro, animal, human observational or intervention) using beer and considering phenols. Overall, data reported so far support the existence of the somehow additive or synergistic effects of phenols and ethanol present in beer. However, findings are inconclusive and thus deserve further animal and human studies.

Potential probiotic and food protection role of wild yeasts isolated from pistachio fruits (Pistacia vera).

BACKGROUND: The biotechnological potential of yeasts from nuts such as pistachio, not only for health applications but also for industry use, has been scarcely studied. Interest in the probiotic capability of yeasts has increased in the past years as well as their utilization as food or feed preservatives. Their capabilities as biocontrol against problematic (spoilage or toxigenic) microorganisms or as antioxidants have been revalued. As a result, both abilities would be desirable to develop a new potential probiotic microorganism which could be added to food or feed to improve their properties. RESULTS: Molecular techniques allowed the identification of a total of seven different species and 15 strains. A screening of the probiotic potential of these strains was carried out. It was found that 65% of the strains resisted the gastrointestinal conditions as well as presented a generation time of < 22 h. Additionally, some strains showed better kinetic parameters than Saccharomyces boulardii (positive control). Complementary tests were done to determine their auto-aggregation capacity, cell surface hydrophobicity, behaviour in a sequential simulated digestion, biofilm formation capability and carbon source assimilation. Finally, 67% and 13% of the studied yeasts showed biocontrol and antioxidant activities, respectively. CONCLUSIONS: Diutina rugosa 14 followed by Diutina rugosa 8 were the best wild yeast from Pistacia vera as potential probiotic and in carbon source utilization. However, Hanseniaspora guilliermondii 6 and Aureobasidium proteae 5 could be used to improve food or feed product preservation because of their notable biocontrol and antioxidant capabilities. © 2020 Society of Chemical Industry.