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Effect of high pressure homogenization on skim milk proteins
Abstract
Skim milk was heated to 40 and 75'C and homogenized at 0, 20, 40, 60, 80 and 1 00 MPa. Residual milk fat was removed by centrifugation at 4400xg for 10 min. A heat treatment control not exposed to homogenization was prepared by heating milk to simulate the time and temperature profile to which samples were subjected during homogenization and cooling. The protein concentration of each sample was determined using the Coomassie Blue Protein Assay Reagent. The protein concentration of samples was equalized and the samples were denatured using reducing and nonreducing buffer before electrophoresis using 10, 14 and 16% acrylamide gels. Gels were stained and scanned to obtain the densities of protein bands for a.-casein, 0-casein, K-casein, []lactoglobulin, []-lactalbumin, bovine serum albumin, lactoferrin and unidentified proteins with molecular weights of 161.9, 124.4, 81.5, 74.4 and 56.3 kd. Protein concentrations were determined by comparing the density of stained bands to the density of a standard with a known concentration. Homogenization inlet temperature significantly (P<.Ol) affected the percentage of the proteins in milk. The greatest changes in the distribution of proteins were observed between inlet temperatures of 40 and 75'C when the protein concentration was determined using nonreducing electrophoresis. The effect of homogenization pressure on the distribution of proteins was significant (P<.01) for all proteins except (X.-casein and the effect of the interaction of homogenization pressure and inlet temperature on the percentage of protein was significant (P<.O I) for all proteins except 0-casein when the protein concentration was determined using nonreducing electrophoresis. The variations in protein concentration were mainly caused by heat denaturation which resulted from homogenization at an inlet temperature of 75'C. For milk homogenized at 75'C, data obtained using reducing electrophoresis showed a significant change in the concentration of proteins, which indicates that disulfide interactions were generated during homogenization. However, the results from the heat simulation study indicated that effects due to homogenization pressure in addition to temperature contributed to the changes in the distribution of proteins in the samples, denaturation and interaction. These effects were possibly due to a pressure effect or a valve design effect.
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Citation
Liu, Yen-Hsiao (1995). Effect of high pressure homogenization on skim milk proteins. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -L5725.
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