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Volume 82, Number 2, March-April 2002
Page(s) 181 - 191

Lait 82 (2002) 181-191
DOI: 10.1051/lait:2002003

Contribution of plasmin to primary proteolysis during ripening of cheese: effect of milk heat treatment and cheese cooking temperature

Joanne M. Somers and Alan L. Kelly

Department of Food Science, Food Technology and Nutrition, University College Cork, Ireland

(Received 22 January 2001; accepted 26 June 2001)

The effects of milk heat treatment and cooking conditions during cheese manufacture on plasmin activity and proteolysis during ripening were determined. Milk heat treatments studied were raw (no heating), 63 °C for 30 min and 75 °C for 1, 5 or 10 min. In separate experiments, cooking temperatures of 38, 43, 48 and 55 °C were examined. Varying cooking temperature did not significantly affect cheese composition except that moisture content was significantly lower ( P < 0.05) at higher cooking temperatures and salt content also significantly ( P < 0.001) differed between treatments. Increasing cooking temperature increased plasmin activity and plasminogen activation during ripening, but decreased chymosin activity, as seen from urea-PAGE analysis. Increasing severity of milk heat treatment had no significant effects on cheese composition, but decreased plasmin activity in cheese and, overall, had less significant effects on proteolysis during ripening than cooking conditions. Thus, the importance of activators and inhibitors of the plasmin system, and their heat stability, in cheese ripening, and the effect of processing, conditions thereon, were apparent.

Contribution de la plasmine à la protéolyse primaire pendant l'affinage de fromage : effet du traitement thermique du lait et de la température de chauffage du caillé. Le présent travail traite des effets du traitement thermique du lait et des conditions de chauffage du caillé lors de la fabrication du fromage sur l'activité de la plasmine et la protéolyse pendant l'affinage. Les traitements thermiques ont été étudiés sur du lait cru (sans chauffage), du lait chauffé à 63 °C pendant 30 min et 75 °C pendant 1, 5 et 10 min. Différentes températures de chauffage du caillé ont été examinées séparément : 38, 43, 48 et 55 °C. Faire varier la température de chauffage du caillé n'a pas affecté significativement la composition du fromage, à l'exception de la teneur en humidité qui a significativement diminué ( P < 0,05) aux plus hautes températures et de la teneur en sels qui était significativement ( P < 0,001) différente entre les traitements. L'augmentation de la température de chauffage du caillé a entrainé l'augmentation de l'activité de la plasmine et de l'activation du plasminogène lors de l'affinage, mais a diminué l'activité de la chymosine, comme l'ont montré les déterminations enzymatiques spécifiques et l'analyse PAGE-urée. Augmenter la sévérité du traitement thermique du lait n'a eu aucun effet significatif sur la composition du fromage, mais a diminué l'activité de la plasmine, et, dans tous les cas, a eu un effet moins significatif sur la protéolyse lors de l'affinage que les conditions de chauffage du caillé. L'importance des activateurs et inhibiteurs du système de la plasmine, et de leur thermostabilité, pendant l'affinage et l'effet des conditions de fabrication a donc été mise en évidence.

Key words: cheese / pasteurisation / cooking / plasmin / proteolysis

Mots clés : fromage / pasteurisation / chauffage du caillé / plasmine / protéolyse

Correspondence and reprints: Alan L. Kelly Tel.: (353) 21 4903405; fax: (353) 21 4270213;

© INRA, EDP Sciences 2002

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