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Cardoso Freitas Lopes de Freitas, Ana Cristina
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- 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.
- 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 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.