Browsing by Author "Pimentel, L. L."
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- Acidifying and aromatic properties of enterococcus strains in ovine and bovine milksPublication . Pimentel, L. L.; Soares, J. C.; Pintado, M. M. E.; Pintado, A. I. E.; Gomes, A. M. P.; Ferreira, A. C.; Malcata, F. X.Enterococci are lactic acid bacteria present in a wide variety of dairy and other food products. Although their presence in the former has been considered an indicator of poor hygienic conditions, nowadays a number of biotechnological and probiotic useful characteristics are already known. A few compounds resulting from the bacterium metabolism contribute to the aroma of cheese. Knowledge of those components, as well as of the acidifying capacity is very important to the dairy industry, including application toward selection of strains as better starters. The aim of this research effort was to study the role of some enterococci in ovine and bovine milks, in terms of acidifying properties and aroma potential. A total of seven strains, previously isolated from traditional Portuguese cheeses, were assayed for: Enterococcus faecium 28A, E. durans 13 and E. faecalis 6 (from Serra da Estrela cheese); and E. faecium 42, E. durans 15, E. faecalis 3 and E. casseliflavus 40 (from Terrincho cheese). Sterilized ovine and bovine milks were inoculated with 2% (v/v) inoculum and incubated at 37 °C. Microbiological viable counts on M17 agar, pH and titrable acidity were determined in duplicate at 0, 1, 4 and 7 d of incubation. Free fatty acids, recognized as strong odorants in Serra da Estrela and other traditional Portuguese cheeses, were quantified in each sample using SPME – GC/MS. All strains showed similar growth patterns, either in bovine or ovine milks, and reached levels of 108 –109 cfu/ml by 1 d of incubation (except E. durans 13, which exhibited a better growth in bovine than ovine milk). An important decrease in pH was observed in both types of milk by 1 d, for all strains. The highest reduction was observed for E. casseliflavus 40 and E. durans 15 in bovine milk, and for E. faecium 42 and E. durans 13 in ovine milk. Enterococcus faecalis 6 revealed the poorest acidification power.
- Acidifying and aromatic properties of enterococcus strains in ovine and bovine milksPublication . Pimentel, L. L.; Soares, J. C.; Pintado, M. E.; Pintado, Ana I. E.; Gomes, Ana M. P.; Ferreira, A. C.; Malcata, F. X.
- Antimicrobial Susceptibility of Enterococci Isolated from Terrincho CheesePublication . Pimentel, L. L.; Novais, C.; Pintado, M. E.; Gomes, Ana M. P.; Coque, T.; Sousa, J. C; Malcata, F. Xavier; Peixe, L.
- Characterization of potential CLA-producing strains according to LA tolerancePublication . Fontes, A. L.; Pimentel, L. L.; Salsinha, A. S.; Cardoso, B.; Andrade, J. C.; Rodríguez-Alcalá, L. M.; Gomes, A. M.Introduction: Linoleic acid (LA) present in ruminants diet goes through a series of reactions within the rumen, called the biohydrogenation pathway. This pathway ends up converting LA to stearic acid (C18), but several intermediate products are formed, such as conjugated linoleic acid (CLA) isomers, which have been extensively studied for their potential bioactive properties1,2. Different ruminal bacteria are involved in this process, however, strains of lactobacilli, bifidobacteria and propionibacteria isolated from human intestine and dairy products have also demonstrated the ability to produce those fatty acids3. Most in vitro CLA production assays normally test potential producing strains by culturing them in the presence of a pure LA solution at 0.5 mg/mL or less4. However, possibly there are some strains that can tolerate higher concentrations of LA and if they are producers, CLA yields may probably be higher. Objective: The major aim of this work was to determine the maximum LA concentration that potential CLA-producing strains can tolerate in further in vitro production assays. Conclusions: In conclusion, potential CLA-producing strains exhibit different LA tolerance degrees, being lactobacilli the more tolerant at the highest LA concentration assayed. Currently overlooked, this is an important parameter to consider in future production tests.
- In situ CLA and CLNA production: a potential strategy to elaborate food products enriched in bioactive fatty acidsPublication . Pimentel, L. L.; Fontes, A. L.; Gomes, A.; Rodríguez-Alcalá, L. M.Conjugated linoleic acid (CLA) and, more recently, conjugated linolenic acid (CLNA) isomers have shown potential to be applied as new functional ingredients, given its bioactive potential to exert benefits to human health. These fatty acids are naturally produced by rumen bacteria that convert linoleic acid (LA) and linolenic acid (LNA) into their conjugated forms. However, strains of lactobacilli, bifidobacteria and propionibacteria have also revealed capacity to produce these compounds. Thus, the aim of this work was to test the in situ production of CLA and CLNA isomers in a dairy matrix using a potential producing strain, in order to verify the suitability of this strategy for CLA and CLNA enrichment in food products. Bifidobacterium breve NCIMB 702258 was selected for this study as previously showed CLA/CLnA production capacity. Its CLA/CLNA-producing ability was firstly tested by incubation in MRS medium containing LA, -LNA or both (at 0.5 mg/mL each) for 24 h at 37 ºC. Fatty acid concentration was analyzed in the supernatant through gas chromatography and it was revealed LA and -LNA conversion rates of, respectively, 30.36% and 67.33%, when substrates were added separately, and of 14.83% and 55.40%, when together, being CLNA production higher than CLA in both situations. Bifidobacterium breve producing capacity was then tested in a food matrix (semi- skimmed milk, 1.6% fat) under the same conditions applied in MRS medium. CLA/CLNA isomers production was positive although substrate conversion rates were lower than those obtained in MRS medium. -LNA conversion was higher than LA when the substrates were added separately (28.09% and 24.19%, respectively), but not when both LA and -LNA were assayed together (14.55% and 27.60%, respectively). In conclusion, in situ production of microbial CLA and CLNA isomers is a strategy with potential to be applied in the future elaboration of CLA- and CLNA-enriched food products.
- Optimization of linoleic acid emulsion preparation to reduce substrate losses after filter-sterilizationPublication . Fontes, A. L.; Pimentel, L. L.; Salsinha, A. S.; Cardoso, B.; Andrade, J. C.; Gomes, A. M.; Rodríguez-Alcalá, L. M.
- Stability of a lyophilized milk enriched with microbial CLA/CLNAPublication . Fontes, A. L.; Pimentel, L. L.; Rodríguez-Alcalá, L. M.; Gomes, A. M.Conjugated linoleic (CLA) and conjugated linolenic (CLNA) acids have been described with potential bioactive properties. Due limited availability in their natural sources (e.g. ruminants’ milk and meat or vegetable oils), in situ microbial production in dairy products may potentially improve CLA/CLNA daily intake. Several probiotic strains have been reported to produce CLA/CLNA isomers using linoleic (LA) and alpha-linolenic (α-LNA) acids as precursor substrates, respectively. Previous work by this research team led to the formulation of a CLA/CLNA-enriched lyophilized milk, using Bifidobacterium breve DSM 20091 and hydrolysed flaxseed oil (FSO; rich in α-LNA). Since CLA, CLNA, LA and α-LNA are polyunsaturated and prone to oxidation, this research aimed to investigate if this new functional milk product is stable at conditions mimicking shelf-life. Pasteurized cow milk (100 mL) inoculated with B. breve DSM 20091 and hydrolysed FSO or not (control) was fermented for 22 h at 37 ºC under anaerobic conditions. Afterwards, samples were lyophilized and stored at room temperature in an exicator, being air- and light-protected. Samples were taken at the beginning (T0wk) and every 4 weeks until the end of the assay (T12wk) for further microbial counting and fatty acid (FA) analysis. Concerning to B. breve DSM 20091 viable cell counting, counts remained below the countable range during the entire study, so as total microbial counting. As for FA analysis, in the non-esterified fraction, the CLA and CLNA contents in the enriched milk product increased after 4 weeks (up to 1.80 and 11.12 mg/g, respectively) and, thereafter, no significant differences were detected. The same was observed for total polyunsaturated FA, but, in the esterified fraction, its level increased significantly after 8 weeks (up to 6.01 mg/g) and then reduced to 5.18 mg/g at the end of the study. In conclusion, a lyophilised milk enriched with microbial CLA/CLNA is not entirely stable, including its CLA/CLNA content, which was inclusively enhanced.
- Study of virulence factors in Enterococci isolated from cheesePublication . Pimentel, L. L.; Semedo, T.; Gomes, Ana M. P.; Pintado, M. E.; Tenreiro, R.; Crespo, M. T. B.; Malcata, F. Xavier
- Survival of potentially probiotic enterococci in the GI tractPublication . Pimentel, L. L.; Matto, J.; Gomes, Ana M. P.; Pintado, M. E.; Malcata, F. Xavier; Saarela, M.
- Tolerance of Enterococci to bile saltsPublication . Pimentel, L. L.; Pintado, Manuela E.; Pintado, Ana I. E.; Gomes, Ana M. P.; Malcata, F. X.