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Cardoso Freitas Lopes de Freitas, Ana Cristina
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- Role of dominant microflora of Picante cheese on proteolysis and lipolysisPublication . Freitas, A. Cristina; Pintado, Ana I. E.; Pintado, Manuela; Malcata, F. XavierFour species of bacteria (Enterococcus faecium and E. faecalis, Lactobacillus plantarum and Lb. paracasei) and three species of yeasts (Debaryomyces hansenii, Yarrowia lipolytica and Cryptococcus laurentii) isolated from Picante cheese were assayed for proteolytic and lipolytic activities. The milk type (caprine or ovine), the ripening time (0–65 d) and the concentration of NaCl (0–14% (w/v)) have been studied in terms of their effects upon in vitro curdled milk. Proteolytic and peptidolytic activities were demonstrated to be high for Y. lipolytica, and at much lower levels for the other strains. Milk type, ripening time and content of NaCl appeared to be statistically significant processing factors in terms of proteolysis. Clear lipolytic activity was detected for Y. lipolytica, but release of free fatty acids to lesser extents was observed for the other strains under study. Ripening time was statistically significant for lipolysis but milk type was not. Lipolytic activities were strongly affected by NaCl content and the extent of fat hydrolysis was affected by the increase of NaCl from 0 to 7% (w/v) more than by change from 7 to 14% (w/v). In view of the experimental results, a mixed-strain starter for Picante cheese including Lb. plantarum, E. faecium (or E. faecalis) and D. hansenii (and/or Y. lipolytica) is of potential interest.
- How milk type, coagulant, salting procedure and ripening time affect the profile of free amino acids in Picante da Beira Baixa cheesePublication . Freitas, A. C.; Fresno, J. María; Prieto, Bernardo; Franco, Imaculada; Malcata, F. Xavier; Carballo, JavierThe concentration of total free amino acids (FAA) in Picante cheese increased with ripening time irrespective of the particular protocol used for manufacture (ie ratio of caprine to ovine milks, animal or plant rennet and number of salting steps). The experimental cheeses manufactured with 20% (v/v) caprine milk, coagulated with animal rennet and salted only once exhibited the highest content of total FAA by 120 days of ripening. All four manufacture parameters were statistically significant on the 0.5% level of significance in terms of total concentration of FAA. The dominating free amino acids present in the various experimental cheeses throughout the ripening period were valine, leucine and phenylalanine, each one representing more than 10% (w/w) of the total concentration of FAA. All four manufacture parameters were, in general, statistically significant with respect to the content of every single FAA, with particular emphasis on salting and ripening time.
- Michaelis-menten kinetics: explicit dependence of substrate concentration on reaction timePublication . Freitas, A. Cristina; Malcata, F. XavierThe nonlinear dependence of the rate expressions associated with enzymecatalysed reactions on the concentration of substrate implies that the corresponding integrated form of the substrate mass balance in a batch reactor cannot be expressed as an explicit function of time..This paper addresses this problem for the classical case of Michaelis—Menten kinetics by providing a self-pacing exploration of the characteristics of a Taylor expansion of the substrate concentration on time. The accuracy of such an approximation is discussed. The procedure presented is appropriate to model situations of technological and practical interest.
- Organic acids produced by lactobacilli, enterococci and yeasts isolated from Picante cheesePublication . Freitas, A. Cristina; Pintado, Ana I. E.; Pintado, Manuela E.; Malcata, F. XavierFour species of bacteria (Enterococcus faecium and Enterococcus faecalis, Lactobacillus plantarum and Lactobacillus paracasei) and three species of yeasts (Debaryomyces hansenii, Yarrowia lipolytica and Cryptococcus laurentii), previously isolated from Picante cheese, were cultured in ovine and in caprine milk and assayed for sugar and organic acids metabolism for 6 days. The results indicated that both milk types can be coagulated by the four strains of lactic acid bacteria. Lb. paracasei led to a faster and greater reduction in pH. Production of lactic acid correlated to lactose degradation, and was highest for Lb. paracasei followed by E. faecium; citrate metabolism was apparent for E. faecalis and, to a lesser extent, for E. faecium, Lb. plantarum and Lb. paracasei. Relatively high contents of formic acid were found when inoculation was with Enterococcus and with Lb. plantarum.
- Microbiological characterization of picante da Beira Baixa cheesePublication . Freitas, A. Cristina; Pais, Célia; Malcata, F. Xavier; Hogg, TimNinety cheeses of the type Picante da Beira Baixa (a hard, highly salted, and spicy traditional cheese produced in Portugal from a mixture of goat's and ewe's milks) were manufactured and analyzed for microbiological quality at different stages of the 180-day ripening period. The most abundant species of Enterobacteriaceae, staphylococci, enterococci, lactobacilli, and yeasts found in the Picante cheese were Hafnia alvei and Serratia liquefaciens; Staphylococcus hominis and S.xylosus; Enteroccus faecium, E. faecalis, and E. durans; Lactobacillus plantarum and L. paracasei; and Debaryomyces hansenii and Yarrowia lipolytica.
- Effects of ripening time and combination of ovine and caprine milks on proteolysis of Picante cheesePublication . Freitas, A. Cristina; Fresno, J. Maria; Prieto, Bernardo; Malcata, F. Xavier; Carballo, JavierProteolysis in Picante cheese was characterized by assaying for breakdown products throughout a 180 day ripening period using different combinations of ewe's and goat's milks. Parameters analysed were total nitrogen (TN), water-soluble nitrogen (WSN) and non-protein nitrogen (NPN) using Kjeldahl and spectro-photometric methods, and casein profile by electrophoresis. WSN at 180 days of ripening was 25–29% TN. The maximum NPN values were attained by 180 days of ripening and corresponded to 87% and 92% of the WSN in 0C and 100C, respectively (where iC denotes a cheese manufactured with i% caprine milk). Statistically significant correlations were obtained between the various analytical methods of assay for nitrogen and ripening time. The spectrophotometric methods using either trinitrobenzenesulphonic acid or cadmium-ninhydrin proved satisfactory in assessing the ripening index (instead of the Kjeldahl method). Degradation of β-caseins at 180 days was 18.8, 26.4, 40.2, 55.6 and 36.5% for 0C, 25C, 50C, 75C and 100C, respectively. Degradation of αs-caseins by 180 days was 35.9, 40.2, 81.8, 93.0 and 68.7% for 0C, 25C, 50C, 75C and 100C, respectively. In general, a higher cheesemaking milk fraction of caprine milk was associated with higher amounts of γ-caseins.
- Influence of milk type, coagulant, salting procedure and ripening time on the final characteristics of picante cheesePublication . Freitas, A. Cristina; Malcata, F. XavierPicante da Beira Baixa cheese is a hurd, spicy, salty traditional cheese with a minimum ripening time of 120 d that is manufactured in Portugal at a farm level 0nly. The purpose of this work was to study the influence of several manufacturing conditions (viz. mixture of ovine and caprine milks, source of coagulant, level of NaCl addition, and duration of ripening period) on the final characteristics of this cheese following a (replicated) factorial design. Milk type proved to be a statistically significant technological parameter in terms of numbers of viable microorganisms of various genera and the extent of proteolysis, probably us u consequence of higher initial contamination of caprine milk. The type of coagulant ad a major effect on proteolysis: values of water-soluble nitrogen for cheeses coagulated with animal rennet were in general lower than those for cheeses coagulated with plant rennet, but much smaller differences were detected between values of non-protein nitrogen; and breakdown of a3 and b-caseins was more extensive in Picante cheeses manufactured with plant rennet. The level of NaCl was a statistically significant parameter ,for all microbiological, physicochemical and chemical Characteristics measured, an observation that is probably due to its capacity to reduce water activity. Ripening time did not have a significant effect on the numbers of viable staphylococci.
- Influence of milk source and ripening time on free amino acid profile of Picante cheesePublication . Freitas, A. Cristina; Fresno, J. María; Prieto, Bernardo; Franco, Inmaculada; Malcata, F. Xavier; Carballo, JavierThe evolution of concentration of free amino acids in Picante cheese throughout ripening was studied for several volumetric ratios of ewe's and goat's milks. The concentrations of all free amino acids, except asparagine, γ-aminobutyric acid, and cysteine, generally increased as ripening time elapsed. Analyses of variance have indicated that ripening time and, to a lesser extent, milk composition have significant effects on the overall concentration of free amino acids. The major free amino acids present in the various cheeses along the ripening period were valine, leucine, and phenylalanine; these three amino acids accounted for 50, 49, 57, 46 and 42% of total free amino acids at 0 days and 42, 42, 43, 39 and 36% of total free amino acids at 180 days for cheeses manufactured with 0, 25, 50, 75 and 100% goat's milk, respectively. Significant differences could be detected in terms of amino acid profile when the relative proportions of ewe's and goat's milks were altered (eg valine changed from 251.79 ± 0.99 to 352.20 ± 16.49 mg/100 g of dry matter, leucine from 181.48 ± 1.77 to 226.00 ± 11.60 mg/100 g of dry matter, and phenylalanine from 120.39 ± 1.44 to 155.36 ± 8.39 mg/100 g of dry matter in 140-day ripened cheeses when plain ewe's milk was replaced by plain goat's milk). The correlation coefficients between the concentrations of valine, isoleucine, leucine and phenylalanine, on the one hand, and ripening time, on the other, were greater than 0.93.
- Technological optimisation of Picante cheese using microbiological, chemical and physical criteriaPublication . Freitas, A. Cristina; Malcata, F. XavierIn order to optimise the final quality of Picante cheese, several processing parameters (i.e., volumetric fraction of caprine milk, ripening time and percentage of salt added to fresh cheese) were manipulated and gave rise to a number of experimental cheeses produced according to a second-order, composite factorial design. Microbiological, physicochemical, biochemical and textural analyses were carried out in samples from all experimental cheeses. The most important effect in microbiological terms was produced by ripening time, in both linear and quadratic forms; caprine milk fraction and amount of salt added were also found to be significant factors, again in both linear and quadratic forms, especially with respect to total viable mesophilic microorganisms, Enterobacteriaceae and staphylococci. In terms of proteolysis and lipolysis, ripening time was the dominant factor, but caprine milk fraction and NaCl content were also significant at the 5% level. A higher content of caprine milk was associated with higher extents of proteolysis and lipolysis, but the reverse held for NaCl content. It was concluded that 50–80% (v/v) caprine milk, ripening for 195 days and 15% (w/wTS) NaCl provide safe counts of Enterobacteriaceae and staphylococci, while maximising proteolysis and lipolysis in Picante cheese.
- Lipolysis in Picante cheese: Influence of milk type and ripening time on free fatty acid profilePublication . Freitas, Ana C.; Malcata, F. XavierChanges in the profile of the major free fatty acids (FFA) were assayed by HPLC up to 180 days of ripening in batches of cheeses manufactured with different proportions of ewe's and goat's milks. Evolution of lipolysis was also monitored by ethanolic titration, and good linear correlations were found between the two methods. For every batch of cheese, concentrations of all FFA exhibited continuous increases throughout the ripening period; levels of total FFA by 180 days of ripening ranged from 50.3 to 62.3 g / kg of fat depending on the cheesemilk composition; C1o, C16, C18, and C18:1, were the most concentrated FFA throughout the whole ripening period. Values for the short chain FFA (C4, C6, and C8) ranged from 2.8 to 4.5 g / kg of fat; such concentrations, which were not significantly different between batches with different proportions of ewe's and goat's milks, contributed considerably to the characteristic piquant flavor of Picante cheese.