Percorrer por autor "Sousa, M. J."
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- Comparison of plant and animal rennets in terms of microbiological, chemical, and proteolysis characteristics of ovine cheesePublication . Sousa, M. J.; Malcata, F. X.Cheeses manufactured from ovine raw milk using crude aqueous extracts of flowers of Cynara cardunculus as rennet were compared with cheeses manufactured with a commercial animal rennet. Changes in a number of microbiological, chemical, and biochemical characteristics throughout ripening were followed in attempts to get scientific insight especially into the primary proteolysis brought about by this plant rennet in cheese. Using averages and corresponding 95% confidence intervals, it was concluded that the type of rennet had no significant effect on cheese composition (e.g., moisture, fat, protein, salt, and pH at the center and at the surface) over the ripening period but lower microbiological counts of Enterobacteria, Lactococci, and Lactobacilli were obtained for cheese manufactured with plant rennet until 28 days of the ripening. Conversely, several biochemical differences in cheese became apparent as ripening progressed. Electrophoretic analyses of the water insoluble fractions from cheeses manufactured with either rennet showed that β-caseins were less susceptible to proteolysis than αs-caseins and that the animal rennet was more proteolytic on β- and αs-caseins than the plant rennet; cheeses manufactured with the plant rennet exhibited higher levels of WSN/TN than cheeses manufactured with the animal rennet, although the former showed lower levels of TCA/TN and lower levels of PTA/TN. The peptide profiles of water-soluble extracts of the cheeses obtained by reversed-phase HPLC exhibited different patterns at all stages of ripening for the two rennets utilized, thus conveying important qualitative information for fundamental differentiation of proteolysis effected by either rennet.
- Effect of storage and lyophilization on ovine and caprine casein degradation by extracts of Cynara cardunculus (L.)Publication . Tavaria, F. K.; Sousa, M. J.; Malcata, F. X.
- Effects of processing conditions on the caseinolytic activity of crude extracts of Cynara cardunculus LPublication . Sousa, M. J.; Malcata, F. X.Four processing parameters (time of grinding, pH of buffer, salt concentration of buffer, and homogenization time) involved in the liquid extraction of proteinases from flowers of the wild thistle (Cynara cardunculus), were studied for their effects on final caseinolytic activity by a surface response method. The caseinolytic activity was assayed spectrophotometrically using o-phthal dialdehyde. An empirical quadratic model was applied to experimental data pertaining to the average enzymatic activity and equations describing the optimal conditions were obtained. Simultaneous solution of these equations for the local maxima indicated that, within the range tested, the maximum (estimated) specific caseinolytic activity (around 9.5 μmol of equivalent leucine/min.g of thistle flower) was obtained by grinding the flowers for 36 s, using an extrac tion buffer with a pH of 5.9 and a salt content of 0% (w/w), and homogenizing the ground flower/buffer suspension for 15 min. These data are of use in the optimization of extraction proce dures, which are of relevance to the production of standardized plant rennets suitable for the large scale manufacture of ewe's milk cheese.
- Identification of peptides from ovine milk cheese manufactured with animal rennet or extracts of Cynara Cardunculus as coagulantPublication . Sousa, M. J.; Malcata, F. X.Urea-PAGE of the water-insoluble extract (WISE) of ovine raw milk cheeses manufactured with proteinases of Cynara cardunculus or with commercial animal rennet indicated that the animal rennet acts more intensively, in quantitative terms, on ovine â-, Rs1-, and Rs2-caseins than the plant rennet. The water-soluble extract (WSE) from cheese produced by plant rennet was constituted by fragments of ovine â- and Rs2-caseins; peptides â-(f128-*), â-(f166-*), and â-(f191-*) were produced only by plant rennet, whereas peptides â-(f164-*) and â-(f191-*) were produced only by animal rennet. The peptide â-(f1-190) was identified as the primary product of ovine â-casein degradation in the WISE for both rennets. The complementary peptides Rs1-(f1-23) and Rs1-(f24-191) were produced by both rennets from ovine Rs1-casein; however, the bond Phe23-Val24 was cleaved by as early as 7 days in cheese manufactured with C. cardunculus, whereas 28 days had to elapse before that could be detected in the case of animal rennet. The peptide Rs1-(f24-165) was produced only by plant rennet, whereas the peptide Rs1-(f120-191) was produced only by animal rennet. The peptides produced from bovine Rs2-casein in cheese could not be traced as deriving from the action of proteinases from either rennet, so their existence is likely due to proteinases or peptidases released in cheese as a result of its indigenous microflora.
- Influence of pasteurization of milk and addition of starter cultures on protein breakdown in ovine cheeses manufactured with extracts from flowers of Cynara cardunculusPublication . Sousa, M. J.; Malcata, F. X.Ovine cheeses were manufactured from raw milk (R), pasteurized milk without starter addition (P), and pasteurized milk with starter addition (PS), using in all cases extracts of Cynara cardunculus as rennet and mimicking as far as possible the traditional manufacture process. The microbial counts were higher in (R) cheeses than in (P) cheeses, and the lowest microbial counts were found for (PS) cheeses. Such physicochemical characteristics as moisture, fat, protein, NaCl content, and pH of the three types of cheeses were similar to one another at each sampling time. In particular, pasteurization had no significant effect on protein breakdown as evaluated by either the water-soluble nitrogen, the trichloroaceticacid (TCA)-soluble nitrogen, or the phosphotungstic acid (PTA)-soluble nitrogen fractions. However, the TCA-soluble and the PTA-soluble fractions for the PS cheeses ripened for more than 28 days were higher than those for the (R) or (P) cheeses at similar ripening times. The cheeses and their water-soluble extracts could not be distinguished by urea-polyacrylamide gel electrophoresis for up to 7 days, but clear differences were apparent at 68 days of ripening for the (PS) cheeses with respect to the (R) and (P) cheeses.