The effect of immunoglobulins and somatic cells on the gravity separation of fat, bacteria, and spores in pasteurized whole milk

Abstract Text: Our objective was to determine the role that Ig and somatic cells (SC) play in the gravity separation of milk. There were 9 treatments: (1) low temperature pasteurized (LTP) (72°C for 17.31s) whole milk, (2) LTP (72°C for 17.31s) whole milk with added bacteria and spores, (3) recombined  LTP (72°C for 17.31s) whole milk with added bacteria and spores, (4) high temperature pasteurized (HTP) (76°C for 7 min) whole milk with added bacteria and spores, (5) HTP (76°C for 7 min) whole milk with added bacteria and spores and added colostrum, (6) HTP (76°C for 7 min) centrifugal-separated gravity-separated (CS GS) skim milk with HTP (76°C for 7 min)  low SC cream with added bacteria and spores, (7) HTP (76°C for 7 min) CS GS skim milk with HTP (76°C for 7 min)  high SC cream with added bacteria and spores, (8) HTP (76°C for 7 min) CS GS skim milk with HTP (76°C for 7 min) low SC cream with added bacteria and spores and added colostrum, and (9) HTP (76°C for 7 min) CS GS skim milk with HTP (76°C for 7 min) high SC cream with added bacteria and spores and added colostrum. The milks in 9 treatments were gravity separated at 4°C for 23 h.  Five fractions were collected by weight from each of the columns treatments starting from the bottom of the column:  0 to 5%, 5 to 90%, 90 to 96%, 96 to 98%, 98 to 100%. The SC, fat, bacteria, and spores were measured in each of the fractions.  The experiment was replicated in 3 different weeks using a different batch of milk and colostrum. Portions of the same batch of the frozen bacteria and spore solutions were used for all 3 replicates.  The presence of both SC and Ig were necessary for normal gravity separation (i.e., rising to the top) of fat, bacteria, and spores in whole milk. The presence of Ig without somatic cells was not sufficient to cause bacteria, fat and spores to rise to the top without SC.  The interaction between SC and Ig was necessary to cause aggregates of fat, SC, bacteria, and spores to rise during gravity separation. The SC may provide the buoyancy required for the aggregates to rise to the top due to gas within the SC. More research is needed to understand the mechanism of the gravity separation process.

Keywords: Immunoglobulin, somatic cells, gravity separation