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Uncommonly Thorough Hydrolysis of Peptides during Ripening of Ragusano Cheese Revealed by Tandem Mass Spectrometry

Valérie Gagnaire,*,†,‡ Stefania Carpino,§ Concetta Pediliggieri,§ Julien Jardin,†,‡ Sylvie Lortal,†,‡ and Giuseppe Licitra§,∇

†UMR 1253, INRA, Science et Technologie du Lait et de l’0uf, 65 rue de Saint Brieuc, F-35042 Rennes, France
‡UMR 1253, Agrocampus Ouest, Science et Technologie du Lait et de l’0uf, 65 rue de Saint Brieuc, F-35042 Rennes, France
§CoRFiLaC, 25 Km 5, Ragusa Mare, 97100 Ragusa, Italy
∇ Department of Agriculture and Food Production Science, Catania University, via Valdisavoia 5, 95100 Catania, Sicily, Italy

Abstract

Ragusano is a pasta filata cheese produced from raw milk in Sicily. The proteolysis was extensively analyzed after stretching (day 0), at 4 and 7 months of ripening through soluble nitrogen, urea-PAGE, and peptide identification by tandem mass spectrometry. After stretching, 123 peptides were identified: 72 arising from β-casein, 34 from αs1-casein, and 17 from αs2-casein. The main protein splitting corresponded to the action of plasmin, chymosin, cathepsin D, cell envelope proteinase, and peptidase activities of lactic acid bacteria. Unlike other types of cheeses, <10% residual β- and αs-caseins remained intact at 7 months, indicating original network organization based on large casein fragments. The number of identified soluble peptides also dramatically decreased after 4 and 7 months of ripening, to 47 and 25, respectively. Among them, bioactive peptides were found, that is, mineral carrier, antihypertensive, and immunomodulating peptides and phosphopeptides.

KEYWORDS: Ragusano cheese, tandem mass spectrometry, peptide, proteolysis, ripening

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Valérie Gagnaire