Effect of immunoglobulin and milk fat globule membrane on culture agglutination

A model system where homogenized skim was added to heat treated skim was used to determine how various components interact resulting in culture agglutination.;Study 1. The effect of heating skim milk (32, 49, 65, and 82°C) prior to homogenization on culture agglutination (Lactococcus lactis CH970 or E72) was investigated. Homogenization of skim milk heated (49 and 65°C prior to homogenization) reduced agglutination as compared to the unheated control (P < 0.005). When skim milk was heated to 82°C agglutination was inhibited. These data suggested that heat changes the configuration of homogenization active component that interacts with the heat activated component to decrease culture agglutination.;Study 2. The effect of homogenization of skim milk containing added immunoglobulin on culture agglutination was determined. Homogenization of skim milk containing added immunoglobulin reduced culture agglutination. These data showed that sufficient material was present in skim milk that when homogenized, the components were able to tie up the added immunoglobulin sufficiently to decreased the total culture agglutination response.;Study 3. The effect of heating immunoglobulin prior to addition to skim milk on culture agglutination was studied. Immunoglobulin was heated to 65, 70, 75, 80, and 85°C for 5 min. Heated immunoglobulin was added to skim milk, and cultured. Immunoglobulin heated at 65°C before being added to skim milk was less agglutinated (25%) than immunoglobulin heated to higher temperature (70, 75, 80, 85°C). These data suggested that immunoglobulin heated to above 70°C was more active in bridging cells than native immunoglobulin.;Study 4. The effect of added milk fat globular membrane (MFGM) with and without homogenization on culture agglutination was investigated. Addition of MFGM to skim milk increased agglutination at 2% concentration. Homogenization of MFGM enriched skim milk dramatically decreased the agglutination response (P < 0.0001). These data suggested that MFGM decreases the bridging between culture cells. Homogenization of skim milk containing MFGM appears to cause the MFGM to unfold which increases its ability to bind native immunoglobulin. When native immunoglobulin is bound to MFGM less free immunoglobulin is available to bind with culture cells, and culture agglutination is reduced.