Browsing by Author "Mendes-Ferreira, A."
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- 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.
- 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.