k-Casein Heterogeneity and Mild Heating Effects on Susceptibility to Chymosin Action

Authors

  • ZAHUR U. HAQUE,

    1. Author Haque is with the Dept. of Food Science & Technology, P.O. Drawer NH, Miss. State Univ., MS 39762. Author Khalifa's present address: Dairy Science Dept, Faculty of Agriculture, Tanta Univ., Kafr El-Sheikh City, Egypt. Address inquiries to Dr. Haque.
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  • MAHAMMED Y. KHALIFA

    1. Author Haque is with the Dept. of Food Science & Technology, P.O. Drawer NH, Miss. State Univ., MS 39762. Author Khalifa's present address: Dairy Science Dept, Faculty of Agriculture, Tanta Univ., Kafr El-Sheikh City, Egypt. Address inquiries to Dr. Haque.
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  • Journal article #J7739 of the Mississippi Aaricultural & Foreestry Experiment Station, Mississippi State, MS 39762.

  • A Peace fellowship for author Khalifa and a research grant from the National Dairy Promotion and Resesrch Board awarded to author Haque are gratefully acknowledged. Collaboration regarding computer programming was with Professor Yoshiro Kamata as part of a collaborative research agreement between MSU and Miyagi University, Sendai, Japan.

ABSTRACT

Bovine SH-k-casein (k-C-pool) was fractionated into five components based on carbohydrate and sialic acid contents (k-C-P1 < k-C-P2 < k-C-P3 < k-C-P4 < k-C-P5) by ion-exchange chromatography (DEAE-cellulose). Chymosin susceptibility observed by monitoring changes in optical density during enzyme action, varied among the components. This was a reflection of the difference in self-association of the proteins in aqueous dispersion as determined by hydrophobic interaction chromatograph. There was an inverse relationship between surface hydrophobicity of the protein polymers (k-C-P2 >k-C-P3 >k-C-P4 > k-C-P5 > k-C-P4 > k-C-pool) and their susceptibility to chymosin at 37°C, pH 6.8 (k-C-pool >k-C-P1 >k-C-P5 > k-C-P4 > k-C-P3 > k-C-P2). Mild heating decreased susceptibility and affected flocculation of all except the highly glycosilated components k-C-P4 and k-C-P5 reflecting amphipathicity imparted thermostability.

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