Psychrotolerant spore-forming bacterial spoilage of HTST milk pasteurized for 20 seconds at 75, 85, or 90°C and stored at different temperatures.
Psychrotolerant spore-forming bacterial spoilage of HTST milk pasteurized for 20 seconds at 75, 85, or 90ï¿½C and stored at different temperatures.
T. Lott*, N. Martin, S. Murphy, A. Trmcic, M. Wiedmann. Cornell University Ithaca, NY.
In the absence of post-pasteurization contamination (PPC), psychrotolerant, aerobic, gram-positive spore-forming bacteria (PASB) is what typically limits the shelf-life of fluid milk. Reducing spoilage due to PASB is difficult as these bacteria enter the fluid milk continuum in the raw milk and can survive HTST pasteurization. Currently, several strategies are used to reduce the spore levels in raw milk, which may include bactofugation, microfiltration, and controlling the entry of the spores into raw milk on the farm. The goal of the project was to see if shelf-life extension could be achieved with higher HTST temperatures. Approximately 70 L of raw milk from Texas were processed on a pilot-plant scale at 75ï¿½C/20s, 85ï¿½C/20s, or 90ï¿½C/20s. Pasteurized milk from each HTST temperature was then stored at 3ï¿½C, 6.5ï¿½C, or 10ï¿½C, and microbiological quality was monitored through 42 d or until samples reached maximum bacterial concentration. HTST milk was tested for (1) total bacteria count, (2) gram-negative count to test for the absence of post-pasteurization contamination, (3) pH, and (4) particle analysis for the confirmation of coagulation. Additionally, a sample of raw milk was taken to measure total bacteria count, mesophilic spore count (MSC), psychrotolerant spore count (PSC), and total bacteria count after preliminary incubation (13ï¿½C for 18h). Results of a one-way ANOVA showed there was no significant difference (P > 0.05) between total bacterial counts by HTST temperatures within each storage temperature over shelf-life. These results suggest that since there is no extension of shelf-life using HTST pasteurization temperatures above 80ï¿½C, 75ï¿½C is the optimal HTST pasteurization temperature tested as it requires the least energy input and based on other studies would result in reduced risk of cooked sensory defects. Further, it was found that bacterial concentrations exceeded 1,000,000 cfu/mL (where consumers typically begin to sense defects) before changes in other indicators of sensory characteristics were observed (i.e., pH and coagulation).
Keywords: spore, fluid milk, psychrotolerant.
Biography: Tim Lott is a 2nd year Ph.D. student in the Field of Food Science and Technology at Cornell University. He is part of the Milk Quality Improvement Program and his research focuses on shelf-life extension of HTST milk, school milk quality, and shelf-life modeling with Monte Carlo predictions. Tim conducts his research under the advisement of Martin Wiedmann (Dr. med. vet, Ph.D.) and the supervision of Nicole Martin (Ph.D.).