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P. M. TOMASULA1, D. Gregg2, B. Baxt2, L. Rodriguez2, M. Kozempel1, and R. Konstance1. (1) Dairy Processing & Products Research Unit, USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598, (2) Foot and Mouth Disease Research Unit, Plum Island Animal Disease Center/USDA/ARS, PO Box 848, Greenport, NY 11944 Previous studies made using laboratory simulation of High Temperature Short Time pasteurization (LabHTST) to eliminate FMDV in milk have shown that it is not completely inactivated at the legal minimum (71.7 C/15 sec) but was inactivated at times > 20 minutes and temperatures > 100 C. Some of the virus may be resistant to thermal inactivation because it is encapsulated by milk fat. However, LabHTST is a batch heating operation which can over or under predict the delivered thermal process. It is difficult to quantify for short holding times because it is a nonflow process and does not achieve the rapid come-up and cool-down times encountered in continuous flow HTST. The purpose of this study was to determine the effect on FMDV infectivity of pasteurizing whole milk obtained from FMDV-infected cows in a laboratory-scale continuous flow (HTST) pasteurizer equipped with a plate and frame heat exchanger and holding tube. Additional goals were to determine if the flow component enhances pasteurization and to quantify the holding time for the process. Residence time distribution studies were first carried out using tracer to establish holding times. Milk samples, containing FMDV at levels up to 104 pfu/ml, were pasteurized at 72 C and 80 C at nominal holding times of 15 and 45 sec using a 22 experimental design. Virus was not detectable by tissue culture in milk after all pasteurization conditions. However, residual infectivity was demonstrated in pasteurized milk samples inoculated into steers. The animals developed full-blown FMD symptoms. Results indicate that the outcome of continuous HTST, with nominal 15 or 45 sec holding time is similar to that of LabHTST, with up to 4 log of the virus being eliminated. However, even the longer holding time is not effective for complete elimination of viral infectivity as detected by direct animal inoculation.
Session 46, Dairy Foods: General
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