Interactions of whey proteins with milk fat globule membrane proteins during heat treatment of whole milk

摘要

The association of beta-lactoglobulin (beta-Lg) and alpha-lactalbumin (alpha-La) with milk fat globule membrane (MFGM), when whole milk was heated in the temperature range 60-95 degreesC, was investigated using one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and non-reducing conditions. In SDS-PAGE under reducing conditions, beta-Lg was observed in MFGM material isolated from milk heated at greater than or equal to60 degreesC for 10 min; small amounts of alpha-La and kappa-casein were also observed in the MFGM material of milk heated at greater than or equal to 65 degreesC for 10 min and greater than or equal to75 degreesC for 10 min, respectively. However, these proteins were not observed in SDS-PAGE under non-reducing conditions. Two-dimensional SDS-PAGE of MFGM material isolated from heated milk showed that the protein complexes that remained at the top of the nonreducing gel (first dimension) were resolved into beta-Lg, alpha-La and the major original MFGM proteins in the reducing gel (second dimension). These results indicate that beta-Lg and alpha-La associated with MFGM proteins via disulfide bonds during the heat treatment of whole milk. The amounts of beta-Lg and a-La that associated increased with an increase in the temperature up to 80 C, and then remained almost constant. These maximum values for beta-Lg and alpha-La were similar to1.0 mg.g(-1) fat and similar to0.2 mg.g(-1) fat, respectively. Of the major original MFGM proteins, xanthine oxidase and butyrophilin were not affected by the heat treatment of whole milk, whereas PAS 7 was heat labile and PAS 6 decreased to some extent during heating.