17A-10 |
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C. J. KUO, W. J. Harper, P. D. Courtney, A. E. Yousef, and Q. H. Zhang. Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Ct., 110 Parker Food Science Bldg., Columbus, OH 43210-1007 During the manufacture of whey protein concentrates (WPC), whey goes through ultrafiltration before spray drying. The microorganisms in the whey are concentrated and some can grow during the filtration. As a result, the microbial counts on the final product occasionally exceed the specifications. In order to reduce the microbial counts in the retentate after filtration, Pulsed Electric Field (PEF) treatment was chosen as an additional pasteurizing step. The objective of this study was to determine the effect of PEF on the death of S. thermophilus in WPC retentate. Twelve strains of S. thermophilus were tested in 0.1% saline solution. Selected strains also were tested in a reconstituted 20% solids solution of acid WPC (80% protein, pH 4.6). The tested microorganism included six strains of starter and six strains of non-starter cultures isolated from WPC retentate. The experimental setting of PEF was at 300pps (frequency) and 2.6us (duration time). The treated and untreated samples were collected to determine the microbial counts. The effect of PEF treatment on the characteristics of the WPC solution were evaluated for changes in particle size, viscosity, emulsion stability, and gel strength. Inactivation in both saline and WPC solutions increased as the field strength increased. In saline solution at the highest field strength (39KV), the log reduction ranged from 1.0 to 4.8 and averaged 2.9. In 20% T.S. WPC (36KV), log reduction ranged from 1.5 to 4.0 and averaged 2.5. PEF treatment of the WPC solutions reduced the particle size and the viscosity; but had no significant effect on emulsion stability or gel strength upon adjustment to pH 7.0. Overall, the data suggest the PEF treatment may be useful in reducing the microbial population in acid WPC retentate.
Session 17A, Dairy Foods: Cheese and microbiology
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