Browsing by Author "Quintas, Célia"
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- A model of the specific growth rate inhibition by weak acids in yeasts based on energy requirementsPublication . Quintas, Célia; Leyva, J. S.; Sotoca, R.; Loureiro Dias, M. C.; Peinado, J. M.Zygosaccharomyces bailii, a spoilage yeast, capable of metabolic activity in food environments with low pH, low a(W) and in the presence of weak acid preservatives was chosen for a study on the effect of benzoic acid on growth parameters. In batch cultures, under controlled pH, this food preservative inhibited growth, decreasing the specific growth rate (mu) and the yield coefficient (Y-S) on glucose. Data obtained at pH 3.5, 4.0 and 4.5 showed that this inhibition was exclusively promoted by the undissociated form of the acid since the effect was independent of pH when the concentration of the acid was expressed in this form. Moreover, the relationship between the values for mu and Y-S, provided evidence that the specific consumption rate of glucose (q(S)) was not affected by benzoic acid, indicating that the inhibition of growth should be completely explained by a decrease of Y-S. The outcome of parallel experiments performed in continuous culture was that the decrease of Y-S was due to an increase of the maintenance coefficient (m), defined as the fraction of q(S) diverted from growth to cope with stress, represented in this case by the presence of the preservative. Based on these results a model was built, assuming that m increased hyperbolically with the concentration of benzoic acid, from zero in the absence of the acid up to q(S) when growth was completely inhibited. The concentration of the acid, for which m=q(S)/2, is a constant (K-W), and represents a measure of the tolerance for a preservative, in this case benzoic acid. The simple equation mu/mu(0)=1 +/- W/K-W predicts the value of mu for a concentration (W) of the preservative, requiring the knowledge of two parameters: the specific growth rate in the absence of the preservative (mu(0)) and K-W. The equation fitted very well the data of the effect of benzoic acid on the specific growth rate of Z bailii, having K-W=0.96 mM benzoic acid. The model was also validated with other spoilage yeasts grown in the presence of benzoic acid in microtiter plates in an automated spectrophotometer. The values obtained for K-w under these conditions confirm Z bailii as the most tolerant (K-W=2.1 mM) followed by Pichia sp. (K-W=0.78 mM), Saccharomyces cerevisiae (K-W=0.53 mM) and Debaryomyces hansenii (K-W=0.11 mM). (c) 2004 Elsevier B.V All rights reserved.
- Antimicrobial activity of Drosophyllum lusitanicum, an endemic Mediterranean insectivorous plantPublication . Gonçalves, Sandra; Quintas, Célia; Gaspar, Maria Nelma; Nogueira, José Manuel F.; Romano, AnabelaThe aim of this study was to evaluate the antimicrobial activity of Drosophyllum lusitanicum leaf extract against various yeasts and bacteria species, including both standard and clinically isolated strains. The extract exhibited strong antimicrobial activity against all the tested yeast strains with inhibition zones ranging 23.67–42.23mm and with minimum inhibitory concentration (MIC) values ranging 31–63 mgL 1. All the Gram-positive bacteria studied were inhibited by the extract, showing inhibition zones ranging 17.67–43.00mm and MIC values comprising between 15.6 and 250 mgL 1. In contrast, the growth of the tested Gram-negative bacteria was not significantly affected by the extract. Among the microorganisms tested, Staphylococcus epidermidis ATCC 12228 was the most sensitive, presenting the lowest MIC value (15.6 mgL 1), while Enterococcus faecalis ATCC 29212 was the most tolerant (250 mgL 1). The extract of D. lusitanicum was analysed by gas chromatography-mass spectrometry and the major constituent found was plumbagin.
- beta-(1,3)-glucan synthase complex from Alternaria infectoria, a rare dematiaceous human pathogenPublication . Anjos, J.; Fernandes, C.; Silva, B. M. A.; Quintas, Célia; Abrunheiro, A.; Gow, N. A. R.; Gonçalves, TeresaThe fungal cell wall polymer beta-(1,3)-D-glucan is synthesized by the enzyme beta-(1,3)D-glucan synthase that is a complex composed of at least two proteins, Rho1p and Fks1p. Here, we report the nucleotide sequence of a single FKS gene and of the regulatory unit, RHO1 from the dematiaceous pathogenic fungus Alternaria infectoria. The predicted AiFks and AiRho share, respectively, 93% and 100% identity with that of Drechslera tritici-repentis. We also report that the sensitivity to caspofungin of eight different A. infectoria clinical strains is similar, with a MIC > 32 mu g/ml and a MEC of 1 mu g/ml, except for one strain which had a MEC of 1.4 mu g/ml. This same strain exhibited one substitution at the hot spot 2, S1405A, compatible with less susceptible phenotypes, with the other seven strains having no mutations in either hot spot 1 or 2. The relative quantification of the expression of AiFKS and of AiRHO demonstrated a decrease in response to an exposure to caspofungin at 0.5 mu g/ml.
- Bioethanol production using carob pod, as carbon source on submerged fermentationPublication . Lima-Costa, Maria Emília; Sousa, Catarina; Rodrigues, B.; Quintas, Célia; Raposo, SaraIn the latest years the research for new sources of carbon sources, among industry by-products as potential raw material for bioethanol production is a needful and a sustainable strategy for the success of 2nd generation biofuels.
- Chemical and microbial changes during the natural fermentation of strawberry tree (Arbutus unedo L.) fruitsPublication . Cavaco, Teresa; Longuinho, Carla; Quintas, Célia; Carvalho, Isabel Saraiva deAguardente de medronho is the name given in Portugal to a spirit made from the fermented fruit of Arbutus unedo (strawberry tree), a plant grown in the Mediterranean region. In order to gain a better understanding of the fermentation process, as it is performed in the farms, a natural fermentation with wild microbiota was carried out during 36 days, and some physicochemical and microbiological parameters were studied. The microbial parameters analyzed were total viable, lactic and acetic acids bacteria, and yeast counts. The physicochemical parameters monitored were sugars, minerals, ethanol, organic acids and pH. Yeasts were the main responsible for the fermentation of the fruits, as the lactic and acetic acids bacteria are absent. As the fermentation progressed, the sugars increased during the first 2 days and gradually decreased along the fermentation period. Maintaining the good quality of the product could contribute to the preservation and valorization of traditional resources that are of great importance to prevent their disappearance.
- Cost-effective bioethanol production at low content of nitrogen source from carob syrupPublication . Raposo, Sara; Sousa, Catarina; Rodrigues, B.; Lima-Costa, Maria Emília; Quintas, Célia; Rodrigues, F.Ethanol, as biofuel, has received great interest in the latest decades due to its potential as an alternative transport fuel. Nowadays, ethanol can be produced through fermentative processes, using sugar rich agricultural raw material and it may have a significant role in reducing environmental impact of fossil fuels.
- Cracked green table olive from the south of Portugal: the influence of diferent brining conditonsPublication . Rodrigues, Neusa; Cavaco, Teresa; Quintas, Célia; Nunes, CarlaIn the south of Portugal, cracked green olives represent a traditional way of processing table olives. After harvesting and sorting, the olives are washed, broken and immediately brined (Process A) or submitted to various washing steps with water prior to brining (Process B). The objective of this work was to study the effect of different processing treatments on the evolution of microbiological and physicochemical parameters during the fermentation of cracked green olives at a homemade scale and at different temperatures (25 ºC, room temperature and 18 ºC). Yeasts were found to be the dominant group in fermented cracked green table olives. Process A originated brines without countable Enterobacteria, with higher free acidity and higher phenolic content, when compared to brines resulting from Process B, suggesting that cracking and brining them straight away, represent a preferable way of processing olives which may guarantee the safety of the final product.
- The effect of calcium in the fermentation of white cabbage with salicorniaPublication . Pires-Cabral, Patrícia; Pires-Cabral, Paula; Mira, Helena; Quintas, CéliaThis study investigates the fermentation of white cabbage with salicornia and CaCl2 to assess its effect on the fermentation profiles and properties of the final products. Two sets of experiments were performed: A-cabbage with salt and salicornia, and B-cabbage with salt, salicornia, and CaCl2. The fermentative processes were studied through the microbial (lactic-acid bacteria (LAB), coliforms, and fungi), physicochemical (pH, total acidity), and mineral properties. A diminution of pH values (4.07, 3.58) and increased acidity values (0.70, 0.77 g lactic acid/100 mL) were registered at the end of the fermentation period (A and B, respectively). A stationary phase followed the exponential growth of LAB, and a slight decrease was observed (6.01, 5.51 Log CFU/g) in both experiments. A fungi decline was observed during the first week and the coliform populations disappeared after about 13 days of fermentation. Staphylococcus coagulase-positive, Escherichia coli, and Salmonella were not detected in the final products. The utilization of CaCl2 resulted in fermented cabbage with analogous microbial and sensorial characteristics to fermented cabbage without CaCl2 but with an increased hardness. However, Ca interfered with the diffusion of K, Mg, and Zn, resulting in lower levels of these elements in the final product, particularly Zn, which exhibited a reduction of 37%, reducing the nutritional value of the final products.
- Effect of chloride salts on the sensory and nutritional properties of cracked table olives of the Macanilha Algarvia cultivarPublication . Saúde, Cíntia; Barros, Tânia; Mateus, Tania; Quintas, Célia; Pires-Cabral, PaulaThe effect of sodium chloride replacement with potassium chloride and/or calcium chloride in the fermentation brines on the physicochemical, organoleptic and nutritional profiles of cracked table olives was studied using no more than 8% salt. Although all brines led to vigorous fermentation with the desired characteristics of acidity and saltiness, the sensory panel rated the olives fermented in 8%NaCl and 4%NaCl + 4%KCl as the best, in terms of flavor and overall attributes. The olives fermented in the other brines (4%NaCl + 4%CaCl2, 4%KCl + 4%CaCl2 and 2.7%NaCl + 2.7%KCl + 2.7%CaCl2) were not acceptable. Olives fermented in 4%NaCl + 4%KCl had lower fat, carbohydrates, dietary fiber, calories and similar amounts of phenolic compounds and Ca as the 8%NaCl treatment. In addition, the former had increased K (672%) and reduced Na (19%), making them more nutritionally acceptable. This alteration might be beneficial and allow the olive market to reach new customers or present current customers with a potentially healthier product.
- Effect of electrolyzed water as a disinfectant for fresh-cut fruitPublication . Graça, Ana; Salazar, Miguel; Quintas, Célia; Manso, Teresa; Nunes, Carla; Nunes, CarlaIn fresh-cut processing the disinfection is the most important step. This process can affect the quality and the safety of the end product as well as its shelf life. Chlorine is the most used disinfectant in fresh-cut industry but due to its association with environmental and health risks, the development of alternative sanitizers is emergent. Electrolyzed water (EW) may be an alternative to the use of chlorine sanitizers and both acidic electrolyzed water (AEW) and neutral electrolyzed water (NEW) can be used with this purpose. In fact, several studies have shown that EW can be effective in reducing pathogenic bacteria on the surface of fruits and vegetables. This manuscript presents a review of electrolyzed water approaches, its antimicrobial activity in fresh-cut produce and the results of a study undertaken in our laboratory to evaluate the disinfection efficacy of AEW and NEW on fresh-cut apples and oranges. Fresh-cut apples and fresh cut oranges were inoculated with a suspension of Listeria innocua and fresh-cut oranges with Escherichia coli at a concentration of 107 cfu mL-1 and treated with the different solutions. Untreated freshcut fruits were used as control. The best sanitizing treatment for both pathogens and fruits was AEW at 200 ppm of free chlorine applied during 5 minutes.