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1 Riddet Centre, Massey University, Palmerston North, New Zealand
2 Fonterra Research Centre, Palmerston North, New Zealand
Corresponding author: H. Singh; e-mail: H.Singh{at}massey.ac.nz.
The association of ß-lactoglobulin (ß-LG) and
-lactalbumin (
-LA) with milk fat globule membrane (MFGM), when whole milk was treated by high pressure in the range 100 to 800 MPa, was investigated using sodium dodecyl sulfate (SDS)-PAGE under reducing and nonreducing conditions. In SDS-PAGE under reducing conditions, ß-LG was observed in the MFGM material isolated from milk treated at 100 to 800 MPa for 30 min, and small amounts of
-LA and
-casein were also observed at pressures >600 MPa for 30 min. However, these proteins were not observed in SDS-PAGE under nonreducing conditions. These results indicate that ß-LG and
-LA associated with MFGM proteins via disulfide bonds during the high-pressure treatment of whole milk. The amount of ß-LG associated with the MFGM increased with an increase in pressure up to 800 MPa and with increasing time of pressure treatment. The maximum value for ß-LG association with the MFGM was approximately 0.75 mg/g of fat. Of the major original MFGM proteins, no change in butyrophilin was observed during the high-pressure treatment of whole milk, whereas xanthine oxidase was reduced to some extent beyond 400 MPa. In contrast to the behavior during heat treatment, PAS 6 and PAS 7 were stable during high-pressure treatment, and they remained associated with the MFGM.
Key Words: milk fat globule membrane ß-lactoglobulin high pressure sulfydryldisulfide interchange
Abbreviation key: MFGM = milk fat globule membrane, SMUF = simulated milk ultrafiltrate.
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