Browsing by Author "Silva, S. V."
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- Bioactive Peptides in Ovine and Caprine Cheeselike Systems Prepared with Proteases from Cynara cardunculusPublication . Silva, S. V.; Pihlanto, A.; Malcata, F. XavierThe potential angiotensin-converting enzyme (ACE)– inhibitory and antioxidant activities of peptides in water- soluble extracts, obtained from raw and sterilized ovine and caprine cheeselike systems coagulated with enzymes from the plant Cynara cardunculus, were assessed. Prior to the assay, the 3,000-Da permeate from 45-d-old cheeselike systems was fractionated by tandem chromatographic techniques. Several peaks were obtained in each chromatogram, but only some were associated with ACE-inhibitory or antioxidant activity or both. Peptides Tyr-Gln-Glu-Pro, Val-Pro-Lys-Val- Lys, and Tyr-Gln-Glu-Pro-Val-Leu-Gly-Pro-* from β-casein, as well as Arg-Pro-Lys and Arg-Pro-Lys-His-Pro- Ile-Lys-His-* from αs1-casein exhibited ACE-inhibitory activity. Peptides released upon cleavage of the peptide bond Leu190-Tyr191 (either in ovine or caprine β-casein), and corresponding to the β-casein sequence Tyr- Gln-Glu-Pro-*, possessed antioxidant activity.
- Hydrolysis of caseins by extracts of Cynara Cardunculus precipitated by ammonium sulfatePublication . Silva, S. V.; Barros, R. M.; Malcata, F. XavierPolyacrylamide gel electrophoresis (in the presence of urea) and gel permeation chromatography were employed to assess the profile of hydrolysis of caseins and the activity of enzymes contributed by the flowers of the plant Cynara cardunculus on bovine caseins, after previous precipitation with ammonium sulfate or in a plain crude aqueous extract. Results indicated that the qualitative degradation profile of bovine caseins by plant enzymes (cardosins) remains essentially unchanged upon extraction, and quantitative analysis showed that the precipitated fractions had a higher coagulant-to-proteolytic activity ratio; hence, the results showed that inexpensive precipitation with ammonium sulfate can successfully be used as a purification method in the production of that plant coagulant in standardized form.
- Influence of the coagulant level on early proteolysis in ovine cheese-like systems made with sterilized milk and Cynara cardunculusPublication . Silva, S. V.; Malcata, F. X.The effect of coagulant level on the quality and quantity of protein breakdown during the first 24 h of ripening of cheese-like systems, manufactured with sterilized ovine milk using crude aqueous extracts of Cynara cardunculus as coagulant, was experimentally assessed. Urea-polyacrylamide gel electrophoresis was performed on both water-soluble and water-insoluble cheese extracts to monitor the casein degradation pattern; the ripening extension index and the ripening depth index were thus calculated. Peptides from the water-soluble fraction were isolated by reverse-phase, high-performance liquid chromatography and partially sequenced by Edman degradation. Higher residual coagulant levels in curdled milk led to earlier breakdown of caseins, as expected. The primary cleavage sites were Phe105-Met106 in k-casein, Phe23-Val24 in s1-casein, and Leu127-Thr128, Ser142-Trp143, Leu165-Ser166, and Leu190-Tyr191 in β-casein.
- Partial identification of water-soluble peptides released at early stages of proteolysis in sterilized ovine cheese-like systems: Influence of type of coagulant and starterPublication . Silva, S. V.; Malcata, F. X.Cheese-like systems were manufactured from sterilized ovine milk, using crude aqueous extracts of Cynara cardunculus or cardosin A isolated therefrom as clotting agent. The effect of adding a commercial starter culture was also assessed. The impact of the type of coagulant used during the initial 24 h of proteolysis was evaluated via separation of peptides in the watersoluble extracts by reverse-phase HPLC, followed by partial sequencing via Edman degradation. Cardosin A accounted for most events of primary proteolysis. The major cleavage sites were Phe105-Met106 in κ-casein, and Leu127-Thr128, Ser142-Trp143, Leu165-Ser166, and Leu190-Tyr191 in β-casein. The starter culture did not play an active role during the initial stages of ripening.