Percorrer por autor "Mendes-Faia, Arlete"
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- Efeito do etanol no crescimento de bactérias lácticasPublication . Estevinho, Leticia M.; Loureiro, Virgílio; Mendes-Faia, ArleteNeste trabalho foi estudado o efeito do etanol no crescimento-taxa de crescimento, duração da fase lag e produção de biomassa total (medida em absorvância a 600 nm)- de espécies do género Leuconostoc, Pediococcus e Lactobacillus, isoladas de vinhos. This study deals with the effect of ethanol on the growth rate, lag phase and biomass production by several strains classified under the genera Leuconostoc. Pediococcus and Lactobaciflus. Low concentrations of ethanol significantly increased the growth rate of all strains, which intensity was variable with the pH and among the strains. The repressive effect of ethanol, at higher concentrations, on the bacterial growth was more relevant in Leuconostoc than with Lactobaciflus and Pediococcus. Besides, this effect was significantly dependent of the initial pH of the culture medium.
- Effect of different fining agents and additives in white wine protein stabilityPublication . Ribeiro, Tânia Isabel Monteiro; Cosme, Fernanda; Filipe-Ribeiro, Luis; Fernandes, Conceição; Mendes-Faia, ArleteProteins in white wine could become insoluble and precipitate causing the appearance of a haze in bottled wine. Protein instability may be due to intrinsically or extrinsically factor such as protein molecular weight, isoelectric point, ionic strength, alcohol degree and wine pH or storage temperature. These modifications may occur during aging, storage or when diverse wines are blended. The type and concentration of proteins in the wine depends on grape variety, maturation degree and winemaking operations (pre-fem1entative grape maceration, application of tannins, enzymes or bentonite fining). Usually, the treatment for wine protein instability is sodium bentonite fining. The adsorption of wine proteins onto bentonite is due to the cationic exchange capacity of bentonite, which carries a net negative charge and the wine proteins are mostly positive charged at wine pH, and thus can be exchanged onto bentonite. Sometimes even with high level of sodium bentonite wines do not stabilize. Thus, the main purpose of this work is to understand the interaction of different types of bentonites, tannins, carboxylmethylcellulose (CMC) and mannoproteins on white wine protein stability, to get new approaches to stabilize them. Some trials were performed in four white wines with high protein instability. Preliminary results showed that sodium bentonite and mannoproteins increase protein stability, in opposition, CMC and tannins seems to increase turbidity after stability tests, which means more instability. Final results could provide important information to the wine industry to select alternative treatments to remove unstable proteins to maintain or improve wine quality.
- Effect of different fining agents and additives in white wine protein stabilityPublication . Ribeiro, Tânia Isabel Monteiro; Fernandes, Conceição; Filipe-Ribeiro, Luis; Cosme, Fernanda; Mendes-Faia, ArleteOne of the most common physical instability is the development of protein hazes in white wines. Bentonite (B) is widely used for the treatment of protein instability however in excess it adversely affects its sensorial properties. Thus, the main objective of this study was to compare the efficiency of different B and mannoproteins (MP) on removal protein hazes, and then developing new strategies for protein stabilization. Two tests have been used to assess the stability of wines: heat-test and TCA-test. The effects of treatments on phenolic compounds, chromatic and sensory characteristics of wines were evaluated. Results showed that both B and MP increased protein stability but, MP also improved the sensorial characteristics of wines, indicating that can be an alternative to stabilize wine proteins.
- Effect of ethanol on the growth of lactic acid bacteria from winePublication . Estevinho, Leticia M.; Loureiro, Virgílio; Mendes-Faia, ArleteThe effect of ethanol on the growth of lactic acid bacteria isolated from wine was studied in different strains classified under the genera Leuconostoc (A, B), Pediococus (C) and Lactobacillus (D). A factorial analysis was used to study eight ethanol concentrations (0, 2, 4, 6, 8, lO, 12 and 14%) under three different pH values (3.5, 4.0, 4.5).
- Effect of Saccharomyces cerevisiae cells immobilisation on mead productionPublication . Pereira, Ana Paula; Mendes-Ferreira, A.; Oliveira, João Manuel; Estevinho, Leticia M.; Mendes-Faia, ArleteMead is a traditional alcoholic beverage obtained by the fermentation of diluted honey performed by yeasts. In this work the potential of application of immobilised yeast cells on single-layer Ca-alginate or double-layer alginate-chitosan for mead production was assessed for th e first time. The meads produced either with entrapped or free cells were evaluated in terms of quality and aroma profile. The immobilisation procedure had no adverse effect on cell viability, since minor differences were found in fermentation kinetics among the strains and immobilisation systems. The double-layer alginate-chitosan had no advantage compared with the single-layer Ca-alginate, as the number of free cells in the medium, resulting from cell leakage, was similar. Although meads obtained with entrapped yeast cells presented less ethanol and glycerol and more acetic acid, it exhibited larger amounts of volatile compounds. Immobilised cells produced meads with more compounds with fruity characteristics, such as ethyl octanoate and ethyl hexanoate; however the concentrations of undesirable compounds in such meads were also higher. The effect of immobilisation on the aroma profile was important, but the strain contribution was also of major importance. Thus, the sensory analysis of final product gives an important insight on the overall quality.
- High-cell-density fermentation of Saccharomyces cerevisiae for the optimisation of mead productionPublication . Pereira, Ana Paula; Mendes-Ferreira, Alexandra; Oliveira, José M.; Estevinho, Leticia M.; Mendes-Faia, ArleteMead is a traditional drink that contains 8%e18% (v/v) of ethanol, resulting from the alcoholic fermentation of diluted honey by yeasts. Mead fermentation is a time-consuming process and the quality of the final product is highly variable. Therefore, the present investigation had two main objectives: first, to determine the adequate inoculum size of two commercial wine-making strains of Saccharomyces cerevisiae for the optimisation of mead fermentation; and second, to determine if an increase in yeast pitching rates in batch fermentations altered the resulting aroma profiles. Minor differences were detected in the growth kinetics between the two strains at the lowest pitching rate. With increasing pitching rates net growth of the strain ICV D47 progressively decreased, whereas for the QA23 the increasing inoculum size had no influence on its net growth. The time required to reach the same stage of fermentation ranged from 24 to 96 h depending on the inoculum size. The final aroma composition was dependent on the yeast strain and inoculum size. Fourteen of the twenty-seven volatile compounds quantified could contribute to mead aroma and flavour because their concentrations rose above their respective thresholds. The formation of these compounds was particularly pronounced at low pitching rates, except in mead fermented by strain ICV D47, at 106 CFUs/mL. The esters isoamyl acetate, ethyl octanoate and ethyl hexanoate were the major powerful odourants found in the meads. The results obtained in this study demonstrate that yeast strain and inoculum size can favourably impact mead’s flavour and aroma profiles.
- Improvement of mead fermentation by honey-must supplementationPublication . Pereira, Ana Paula; Mendes-Ferreira, Ana; Estevinho, Leticia M.; Mendes-Faia, ArleteThrough honey's fermentation, diverse beverages can be obtained, among which is mead, an alcoholic drink with 8 to 18% of ethanol (v/v). Since honey is a matrix with a low nutrient concentration and other unfavourable growth conditions, several problems are usually encountered, namely delayed or arrested fermentations, unsatisfactory quality parameters and lack of uniformity of the final product, as well as unpleasant sensory properties. In this context, the aim of this work was to optimize mead production through honey-must supplementation with (a) salts, (b) vitamins or (c) salts+vitamins. The effects of the honey-must formulation on the fermentation kinetics, growth profile and physicochemical characteristics of final meads were evaluated. The results showed minor differences in the fermentation profile and time between fermentations with the different formulations. The growth profile was influenced more by the yeast strain than by the supplements added to the honey-must. In general, the honey-must composition did not influence meads' final characteristics, except regarding the SO < inf > 2 < /inf > concentration of the meads produced using the strain QA23. In summary, the addition of salts and/or vitamins to honey-must had no positive effects on the fermentation, growth profile or characteristics of the final products.
- Mead production: effect of nitrogen supplementation on growth, fermentation profile and aroma formation by yeasts in mead fermentationPublication . Pereira, Ana Paula; Mendes-Ferreira, A.; Oliveira, João Manuel; Estevinho, Leticia M.; Mendes-Faia, ArleteMead is an alcoholic beverage, produced since ancient times, resulting from an alcoholic fermentation of diluted honey by yeasts. When it is produced in a traditional manner, mead producers can encounter several problems related to a lack of essential nutrients, such as available nitrogen. Thus, the aim of this study was to evaluate the effect of nitrogen addition to honey-must on the fermentation performance of two Saccharomyces cerevisiae wine yeasts, QA23 and ICV D47, as well as on the mead composition and production of volatile aroma compounds. A portion of honey-must was supplemented with diammonium phosphate (DAP) to achieve the nitrogen concentration required by yeast to complete alcoholic fermentation. The supplementation with DAP reduced the fermentation length to around 7 days, but not all sugars were fully consumed, suggesting that other factors could be interfering with yeast growth. For both yeasts the specific growth rate and final biomass were higher in musts supplemented with DAP. Mead final composition was similar under the two experimental conditions. Analysis of the volatile profile revealed that the concentrations of the volatile fatty acids and volatile phenols were higher in meads supplemented with DAP. The concentrations of ethyl hexanoate, ethyl octanoate and isoamyl acetate were above their perception threshold and were higher in meads supplemented with DAP, which could contribute to the enhancement of the fruity character. This study could be useful for the optimization of mead production and quality improvement.
- Mead production: Fermentative performance of yeasts entrapped in different concentrations of alginatePublication . Pereira, Ana Paula; Mendes-Ferreira, A.; Estevinho, Leticia M.; Mendes-Faia, ArleteMead is an alcoholic drink known since ancient times, produced by yeast fermenting diluted honey. However, the production of mead has suffered in recent years, partially owing to the lack of scientific progress in this field. In this study, two strains of Saccharomyces cerevisiae, QA23 and ICVD47, were immobilized in 2 or 4% (w/v) alginate beads to assess the most effective alginate concentration for yeast immobilization to produce mead. Neither of the alginate concentrations was able to prevent cell leakage from the beads. The fermentation length was 120h for both yeast strains. In all cases, at the end of the fermentation, the number of cells entrapped in the beads was higher than the number of free cells, and the total 4% alginate bead wet weight was significantly higher than the 2% alginate bead wet weight. In addition, the evaluation of mead quality showed that the yeast strain had significantly more influence on the physicochemical characteristics than the alginate concentration. Although the yeasts immobilized in the two alginate concentrations were able to perform the fermentation, further research is needed in order to understand the evolution of the yeast population inside the beads throughout the fermentative process.
- Mead production: selection and characterization assays of Saccharomyces cerevisiaePublication . Pereira, Ana Paula; Dias, Teresa; Andrade, João Verdial; Ramalhosa, Elsa; Mendes-Ferreira, Ana; Mendes-Faia, Arlete; Estevinho, Leticia M.Mead is a traditional alcoholic drink which results from the fermentation of diluted honey. Yeasts used in mead production are, usually, wine Saccharomyces cerevisiae strains. Most of these yeasts are not adapted to the conditions of mead production namely, high sugar levels, low pH values and reduced nitrogen concentrations. The inability of yeast strains to respond and adapt to unfavorable stressful growth conditions, leads to several problems, such as lack of uniformity of the final product, delays and “pouts” fermentations, as well as the production of off-flavors by the yeasts. Therefore, it is necessary to find yeast strains more suitable for mead production.