1,721,071 research outputs found
Influence of Different Aggregation States on Volatile Organic Compounds Released by Dairy Kluyveromyces marxianus Strains
No full textKluyveromyces marxianus has the ability to contribute to the aroma profile of foods and beverages since it is able to produce several volatile organic compounds (VOCs). In this study, 8 dairy K. marxianus strains, previously selected for their adhesion properties, were tested for VOCs production when grown in different conditions: planktonic, biofilm-detached, and MATS forming-cells. It was shown that biofilm-detached cells were mainly able to produce higher alcohols (64.57 mg/L), while esters were mainly produced by planktonic and MATS forming-cells (117.86 and 94.90 mg/L, respectively). Moreover, K. marxianus biofilm-detached cells were able to produce VOCs with flavor and odor impacts, such as ketons, phenols, and terpenes, which were not produced by planktonic cells. In addition, specific unique compounds were associated to the different conditions tested. Biofilm-detached cells were characterized by the production of 9 unique compounds, while planktonic and MATS forming-cells by 7 and 12, respectively. The obtained results should be exploited to modulate the volatilome of foods and beverages and improve the production of certain compounds at the industrial level. Further studies will be carried out to better understand the genetic mechanisms underlying the metabolic pathways activated under different conditions
γ-aminobutyric acid production by Kluyveromyces marxianus strains
No full textAims: Kluyveromyces marxianus dairy strains were tested for γ-aminobutyric acid (GABA) production. The genes involved in GABA catabolism (UGA1 and UGA2) and anabolism (GAD1) were found in K. marxianus genome. Their relative expression was evaluated with primer designed ad hoc. Methods and Results: Strains were grouped on the basis of GAD1 gene sequence. Representative strains for each group were tested for GABA production by high-performance liquid chromatography. All strains produced it at low levels. qRT-PCR showed the absence of a relation between GABA production and GAD1 gene expression. UGA1 and UGA2 genes were not upregulated and low amounts of succinic acid were detected. Conclusions: All strains released a low amount of GABA suggesting that probably it was stored within cells. The different behaviour of strains in terms of GABA and succinic acid production as well as gene expression highlighted the genetic and phenotypic biodiversity of this species. Significance and Impact of the Study: GABA production and genes involved in its catabolism and anabolism were described in a population of dairy K. marxianus for the first time. The variability observed in terms of genetic and phenotypic biodiversity is important especially to exploit this non-conventional yeast as microbial platform
Correlation between IRC7 gene expression and 4-mercapto-4-methylpentan-2-one production in Saccharomyces cerevisiae strains
No full textVolatile thiols are not present in must but are synthesized and released by wine yeasts during alcoholic fermentation. In this study, autochthonous and commercial Saccharomyces cerevisiae strains were characterized for the expression of the main genes involved in thiols metabolism and their production in wine. New primer sets were developed on the basis of the S288c genome to evaluate the expression of Cys3, Cys4, MET17 and IRC7 genes. Obtained data revealed the occurrence of some thiols, for example, 4-mercapto-4-methylpentan-2-one (4-MMP) and 3-mercaptohexan-1-ol (3-MH) in Pecorino white wine. All genes were upregulated, but only for IRC7 was found a correlation with 4-MMP release: strains with the highest production showed the highest transcription level. IRC7 gene could be proposed as target for the selection of S. cerevisiae strains to increase thiols content in wine
Contribution of Pichia manshurica strains to aroma profile of organic wines
No full textIn this study, the volatile compounds produced by 11 Pichia manshurica strains—isolated from spoiled bottled organic wines of Montepulciano d’Abruzzo and filter membranes—were evaluated in must and wine. Moreover, a quick, reliable and inexpensive method to identify this spoilage species was reported. In particular, a species-specific primer pair was developed using 26S rRNA as target gene. Primers were tested on different yeast species and a band of 300 bp was obtained only for P. manshurica strains. More than 70 volatile compounds were identified. The differences were quantitative rather than qualitative and the majority of the strains released compounds associated with off-flavours and off-odours in must and wine. The obtained data revealed the ability of P. manshurica strains to release compounds which could produce off-flavours and odours
Influence of FLO1 and FLO5 genes on aroma profile of sparkling wines
No full textThis study investigated the influence of S. cerevisiae F6789A strain and its derivative mutants – harbouring FLO1 gene deletion (F6789A-ΔFLO1) and FLO5 gene deletion (F6789A-ΔFLO5) – on secondary fermentation, autolysis outcome and aroma compounds production. Data revealed differences in terms of metabolic behaviour leading to the production of sparkling wines with different characteristics. F6789A showed the best fermentation kinetic reaching a pressure of 5 bar inside the bottle, while F6789A-ΔFLO1 and F6789A-ΔFLO5 reached 4 bar and 3.8 bar, respectively. Cell viability was in agreement with fermentation kinetics. In fact, F6789A showed the highest number of cells. An early autolysis was observed for F6789A-ΔFLO5. Differences were observed especially for esters in terms of number and quantity of esters released. In particular, the parental strains produced 39 different esters while F6789A-ΔFLO1 and F6789A-ΔFLO5 27 and 35, respectively. F6789A-ΔFLO5 was the main ester producer with a total amount of about 89 mg/L. Sensory analysis showed that all the strains produced balanced sparkling wines with negative and positive attributes arranged in good proportions, showing good aroma descriptors. Obtained data suggested that FLO1 or FLO5 genes had a pleiotropic effect affecting not only flocculation ability but also other metabolic traits
Investigation of a deteriorated reinforced concrete infrastructure and possible repair
No full textThe results of an extensive experimental investigation on reinforced concrete bridge decks of the Orte-Ravenna highway (E45) in Italy are reported in this paper. The main investigation object is the reinforced concrete slab of the “Fornello” viaduct which was destined to demolition, since it exhibited serious structural deficiencies. The investigation is carried out by using non-destructive techniques, based on ultrasonic evaluation and termography, as well as producing chemical, physical and mechanical characterization of specimens drawn from damaged and undamaged regions of the R/C bridge decks. The distribution of chlorides and sulphates into the slab thickness is analysed by means of ion chromatography, which has revealed also the presence of organic anions such as formiate and acetate. Frost sensitivity of cement paste is detected by mercury porosimetry. The study is aimed to evaluate the level of concrete damage, to investigate the causes of degradation, and to assess a possible strengthening technique for repair
Geopolymeric and cementitious mortars with the same mechanical strength class: Performances and corrosion behaviour of black and galvanized steel bars
No full textIn the prospect of reducing CO2 emissions and landfilling of waste materials, the preparation of sustainable mortars by alkali activation was studied. According to EN 1504-3:2005, geopolymeric and cementitious mortars belonging to different strength classes (R1 ≥ 10 MPa (1450 psi), R2 ≥ 15 MPa (2175 psi) and R3 ≥ 25 MPa (3625 psi)) were tested and compared. Geopolymers were obtained with fly ash or metakaolin and a blend of sodium silicate and NaOH (or KOH). Mortars were tested in terms of workability, dynamic modulus of elasticity, drying and restrained shrinkage and porosimetry. Durability was also investigated in terms of water vapour permeability, capillary water absorption and corrosion of possible embedded rebars during the curing period and wet-dry cycles in 3.5% NaCl solution. Results showed that geopolymers are subjected to higher drying shrinkage but lower restrained shrinkage than cementitious mortars. Water vapour permeability was higher in geopolymers and capillary water absorption was lower especially in fly ash geopolymers than those of cementitious mortars. During the first month, the high alkalinity of geopolymers extends the active state of both black and galvanized steel bars. However, when exposed to chlorides, fly ash geopolymers offer a higher protection to reinforcements than cementitious mortars
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