29D-8 |
Come-up lethality credit in the tubular heat exchanger during HTST processing |
G. B. AWUAH1, Z. Weng2, and S. Economides1. (1) Center for the Development of Research Policy & New Technologies, National Food Processors Association, 1350 I St. N.W., Ste. 300, Washington, DC 20005, (2) Food Processing Systems Div., FMC Corp., 2300 Industrial Ave., Box A, Madera, CA 93639 The motivation for aseptic processing (HTST) has been the achievement of a high quality product compared to traditional techniques. The HTST concept involves rapid heating, holding and cooling to minimize the impact of temperature on heat sensitive nutrients. In typical industrial operations, heat exchanger exit temperatures could range from 270 to 300 F. Currently, the Food and Drug Administration (FDA) recognizes lethality achieved in the holding tube alone. However, such lethal come-up temperatures could contribute significantly to expected lethality. Our objectives were to: (i) conduct microbiological tests to determine come-up contribution to overall lethality at the end of the holding tube, and (ii) verify experimental results using computer simulated data. A 0.5% w/w sodium carboxymethylcellulose (Sigma Chemical Co., St. Louis, MO) solution with Bacillus stearothermophilus spores was chosen for the study. A lab-scale simulator (MicroThermics Inc, Raleigh, NC) operated at temperatures ranging from 250 to 270 F was used for the study. Fluid residence times ranged from 30 to 89, and, 4 to 14 sec in the heat exchanger and holding tube, respectively. A commercial software package (AseptiCAL, FMC FoodTech, Madera, CA) was used to simulate product cumulative lethality. Our results showed that come-up lethality depended on product initial temperature, residence time and temperature in the heat exchanger. Fluid residence time in the heat exchanger could potentially compensate for the effect of comparatively low product initial temperatures. Our results also suggest the existence of a “threshold” residence time below which come-up lethality may not be achieved for a pre-determined heat exchanger exit temperature. It was observed that between 40 to 51% lethality was contributed by come-up to overall lethality. This contribution was based on achieving an Fo of 8.5 min in the holding tube alone. Generally, computer-simulated data gave conservative estimates of cumulative lethality, and compared favorably with experimental results.
Session 29D, Food Engineering: Thermal processes
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