Browsing by Author "Pereira, V."
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- Characterization for enterotoxin production, virulence factors, and antibiotic susceptibility of Staphylococcus aureus isolates from various foods in PortugalPublication . Pereira, V.; Lopes, C.; Castro, A.; Silva, J.; Gibbs, P.; Teixeira, P.Staphylococcus aureus represents a public health challenge worldwide. The aim of this study was the characterization of different food isolates of S. aureus on the basis of their production of enterotoxins, hemolysins and resistance to antibiotics. A total of 148 coagulase-positive staphylococcal strains isolated from different food origins were identified to the species level. By multiplex PCR, 69% of the isolates were shown to be enterotoxigenic (SEs); the most common were sea seg, sea seg sei and seg sei. According to CLSI [CLSI, Clinical and Laboratory Standards Institute, 2007. Performance Standards for Antimicrobial Susceptibility Testing; Fifteenth Informational Supplement. CLSI document M100-S15. Clinical and Laboratory Standards Institute, Wayne, PA], 38% of the isolates were resistant to oxacillin ( 6 mg/mL; MRSA positives) but only 0.68% showed the presence of mecA gene. 70 and 73% of the S. aureus strains were resistant to b-lactams, ampicillin and penicillin, respectively. The virulence pattern was demonstrated to be origin and strain dependent. These findings emphasise the need to prevent the presence of S. aureus strains and SEs production in foods
- Evolution of 5-hydroxymethylfurfural (HMF) and furfural (F) in fortified wines submitted to overheating conditionsPublication . Pereira, V.; Albuquerque, F. M.; Ferreira, A. C.; Cacho, J.; Marques, J. C.As furfural (F) and 5-hydroxymethylfurfural (HMF) are essentially formed from sugar dehydration, especially in food submitted to heat, they can be found in beverages, as well as fortified sweet wines. In order to assess the impact of temperature on Madeira winemaking, three traditional varieties of Madeira wines (Malvasia, Sercial and Tinta Negra Mole) were studied to evaluate the F and HMF contents. The wines were produced by two vinification processes, following traditional and modern methodologies, heated at standard conditions (30 °C and 45 °C, for 4 months) and compared with the same wines submitted to overheating conditions (55 °C, for 4 months). The RP-HPLC-DAD methodology used for the control of F and HMF during the process showed no significant changes in the wines maintained at 30 °C (canteiro) and a noticeable but controlled increase in the wines heated at 45 °C (estufagem) where values up to about 150 mg/L of HMF could be found in sweet wines. The strong relation of this compound with the sugar content and baking temperature stood out in the wines submitted to overheating conditions where values higher than 1 g/L could be found for sweeter wines, with HMF level being in general higher than F. The results clearly suggest that the amount of HMF in these fortified wines can be easily controlled when submitted to adequate conditions of heating during estufagem and storage. Furthermore, different temperatures for the baking of sweet and dry wines may be considered.
- Evolution of Free Amino Acids in Young Madeira Wines Submited to Controlled Heating ConditionsPublication . Pontes, M.; Pereira, V.; Albuquerque, F.; Câmara, J. S.; Ferreira, A. C.; Marques, J. C.