29A-4 |
A rapid method for determining D and z values in a food processing laboratory course |
T. M. TALIAFERRO, L. J. Mauer, K. D. Hayes, and B. M. Applegate, Sr. Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009 Determination of D and z values for bacterial death is an integral part of thermal processing. Traditional methods for determining D and z values (such as the microscopic count of yeast death) are cumbersome and lengthy, and incorporation of these into the classroom is therefore difficult. While enzymatic methods can be used to generate data sets for students to work with, a rapid bacteriological-based D and z value experiment would be useful for students to use in a classroom setting. Our objective was to develop a rapid method for generating D and z value data sets for a junior-level food processing laboratory course. A bioluminescent Pseudomonas fluorescens 5RL containing a salicylate-inducible luxCDABE gene cassette was used as the bacterial culture. Cell death was monitored by measuring luminescence in a Zylux portable luminometer. Data were collected over time (0 – 2min) after bacterial cultures had been exposed to different temperature treatments (37, 40, 42.5, 45 C). Time at each temperature was empirically determined using an endpoint of 90% loss of light/culture as the most severe time/temperature combination. Excellent D and z data sets were generated using this bioluminescent approach to monitor time-temperature treatment effects on luminescence of the Pseudomonas fluorescens 5RL. Students were able to calculate D and z values from these data sets during the in-class lab exercise. Students also were able to see the effect of temperature-time combination treatments on bacterial death by observing decreasing luminescence visible when classroom lights were turned off. A rapid method for the determination of D and z values using a bioluminescent bacterial strain was successfully developed and implemented in a junior-level food processing course. Due to the rapid nature of this method, replicates were generated in-class for each time-temperature treatment.
Session 29A, Education: General
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