标题：Effects of Protein Concentration in Ultrafiltration Milk Retentates and the Type of Protease Used for Coagulation on the Microstructure of Resulting Gels
摘要：Milk retentates (35~ total solids, 13~ protein) obtained by ultrafiltration were diluted with the permeate to 3 . 2, 5.0, 6.5, 10.0, and 13.0% protein and coagulated using conrnerc1al proteases. Rennet or one of microbial proteases isolated from Bacillus potymlxa , Endothla parasfttca, Mucor mtehel, or Mucor pusfllus were used . Coagulation times were decreased with the Mucor proteases as the protein concentrations in the retentates were increased but the coagulation times were increased with B. potymlxa and f. parasltlca proteases under similar conditions . Firmness was higher in gels made from homogenized retentates than from nonhomogenized retentates of the same protein concentrations. Scanning as well as transmission electron microscopy showed in creasing densities of the protein matrices in the gels as the protein concentrations were increased . Large fat globules and their clusters were noticeable in gels made from nonhomogenized retentates. Gelation of homogenized retentates resulted in uniform matrices with the dimensions of the disintegrated fat particles similar to those of casein micelles . These minute fat particles were closely associated with the protein matrix. Firm gels made by coagulating the retentates with rennet consisted of extensively branching casein particle chains whereas softer gels made with a pofymlxa protease consisted of small casein particle clusters.
关键词：Bacillus polymixa protease; Electron microscopy; endothia parasitica protease; gelation of milk; homogenization; microbial proteases; milk retentates; mucor miehel protease; mucor pusillus protease; proteolytic enzymes; ultrafiltration of milk
