Browsing by Author "Gomes, A. M. P."
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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.
- Caracterização físico-química de queijos coalhos maturados: com leites caprino, bovino e mistoPublication . Nascimento, B. M. S.; Amaral, D. S.; Pereira, C. J. D.; Gomes, D. M. G. S.; Baptista, A. S. M.; Gomes, A. M. P.; Pintado, M.; Queiroga, R.The rennet matured cheese is a handmade product traditionally derived from cow's milk, with promising development with goat milk in the Northeast of Brazil. The purpose of this work was to develop and characterize the coalho matured cheese, by means of physical-chemical analysis. The content of total solids, fat and protein demonstrated having decreased along the maturation process, with difference at the level of 5% by the Tukey test between the product's shelf life periods. The reverse perceived with the salt and ashes content. The coalho cheese matured presents a dairy product alternative goats originated from traditional coalho cheese
- Characterization of the microstructure of Terrincho ewe cheesePublication . Gomes, A. M. P.; Braga, T. M.; Pintado, Ana I. E.; Pintado, Maria Manuela; Malcata, F. XavierThe microstructure of Terrincho cheese – a Portuguese traditional cheese bearing a Protected Denomination of Origin, was assessed by scanning electron microscopy (SEM). Terrincho cheese was manufactured according to the traditional protocol using pre-filtered, plain raw ewe’s milk of Churra da Terra Quente breed, without addition of starter of any other type of cultures, and coagulated with animal rennet. The cheeses were salted upon unmoulding, and placed in ripening chambers held at 10–12 °C and 88–89 % relative humidity for a period of 30 days. Cheeses were sampled at 0, 15 and 30 days. Cheese specimens were prepared for SEM by fixing small blocks of cheese (cut from freshly sampled cheeses) in formaldehyde, at room temperature for 1 month, cutting it into 1–2 mm thick slices using sharp razor blades and dehydrating in a graded ethanol series. Slices in absolute ethanol were critical point dried from carbon dioxide, mounted on SEM stubs using adhesive tabs, sputter-coated with gold, and examined using a JEOL scanning electron microscope. The microstructure of the (semi-soft) curd of Terrincho cheese appeared as a continuous casein network possessing a spongy appearance. The various microbial populations present within the cheese were found to grow in the form of colonies, embedded in the casein network and close to the void spaces originally occupied by fat. Microbial colonies were roughly spherical, with bacteria tightly packed in the centre. A similar pattern of microbial growth was observed throughout ripening. Other inclusions were also pinpointed, namely salt crystals.
- Exopolysaccharide production by lactobacillus acidophilus for potential applications in fresh cheesePublication . Pintado, A. I. E.; Truszkowska, K.; Pintado, M. M. E.; Gomes, A. M. P.; Malcata, F. X.Many strains belonging to the group of lactic acid bacteria (LAB) produce exopolysaccharides (EPS). The ability of EPS to act as viscosifying, stabilizing, and/or water-binding agents in various foods makes it an effective natural alternative to commercial synthetic stabilizers, so it may play an important role in the dairy industry. In fact, EPS-producing LAB are not only important in manufacture of yoghurt and fermented milks, but also in cheese production. Recent research efforts have shown that EPS cultures are useful to increase moisture retention and improve functional properties of low-fat Mozzarella cheese and whey cheese. In this work, the ability of Lb. acidophilus to produce EPS, and the performance of two different methods for EPS isolation was investigated. Fermentations were carried out in a Braun Biostat B 2-L fermentor, filled with 1.5 L of MRS broth containing 20 g/L lactose. The yield of the EPS isolation method was tested by adding xanthan gum to the medium. The experiments were carried out at 37 °C, 150 rpm, pH 5.5 under an N2 atmosphere. A 50 mL/L standard inoculum was prepared from a subculture of Lb. acidophilus, previously grown in the corresponding medium for 20 h at 37 °C, and was used to start-up every fermentation batch. Fermentation batches took 48 h, and samples were taken periodically. Growth was monitored spectrophotometrically and by plate enumeration. To optimise EPS isolation, cells and residual polypeptides were removed by centrifugation (4000 rpm for 20 min) upon precipitation via two different processes: addition of pronase E solution and one volume of 20 % trichloroacetic acid, or precipitation with 20 g/kg 5-sulfosalysilic acid. The EPS was precipitated by three volumes of cold ethanol and was collected by centrifugation. The weight of isolated and dried polymers was measured, and the total amount of carbohydrates was determined by the phenol-sulphuric method. Exponential growth took place for ca. 12 h, and EPS was produced mainly during the stationary phase.
- Improvement of whey cheese matrices via incorporation of Lactobacillus acidophilus — proteolytic and glycolytic activities and their impact upon sensory analysisPublication . Pintado, A. I. E.; Araújo, J. C. C.; Pintado, M. M. E.; Gomes, A. M. P.; Malcata, F. X.Requeijão is a highly nutritious soft Portuguese whey cheese, yet with such organoleptic limitations as poor flavour and grainy texture. Furthermore, it offers excellent conditions for survival and growth of lactic acid bacteria, owing to its high water activity, pH above 5.0 and low salt content. The objective of this research effort was thus to study the contribution of Lactobacillus acidophilus LAC 1 to the improvement of the organoleptic quality of Requeijão, via its proteolytic and glycolytic activities. Experimental whey cheese matrices were produced, and subsequently inoculated with L. acidophilus; these matrices, as well as a control curd, were stored at 7 °C, and samples were taken at 0, 2, 7, 14 and 21 d. Cell viability, pH, and fat, protein and moisture contents were assessed. The contents of water-soluble nitrogen (WSN), nitrogen soluble in 12 %(w/v) trichloroacetic acid (TCA) and nitrogen soluble in 5 %(w/v) phosphotungstic acid (PTA), as well as of lactose and organic acids were also determined. Sensory analysis was finally performed, using a five-point scale for the various attributes. L. acidophilus viable cells number remained constant up to 21 d, while pH decreased by ca. 0,6; this was consistent with an increase in lactic acid content up to 28 mg/g of whey cheese. Values of TCA and PTA in L. acidophilus matrices indicated relevant proteolytic breakdown of whey proteins. These matrices received the highest overall preference scores in sensory evaluation.
- Invited review: physiological properties of bioactive peptides obtained from whey proteinsPublication . Madureira, A. R.; Tavares, T.; Gomes, A. M. P.; Pintado, M. E.; Malcata, F. XavierProcessing of whey proteins yields several bioactive peptides that can trigger physiological effects in the human body: on the nervous system via their opiate and ileum-contracting activities; on the cardiovascular system via their antithrombotic and antihypertensive activities; on the immune system via their antimicrobial and antiviral activities; and on the nutrition system via their digestibility and hypocholesterolemic effects. The specific physiological effects, as well the mechanisms by which they are achieved and the stabilities of the peptides obtained from various whey fractions during their gastrointestinal route, are specifically discussed in this review.