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P1-154 Thermal Resistance of the Histidine Decarboxylase Enzymes from High Histamine-producing Bacteria

Monday, August 1, 2016
America's Center - St. Louis
Kristin Bjornsdottir-Butler, U.S. Food and Drug Administration, Gulf Coast Seafood Laboratory, Dauphin Island, AL
F. Aladar Bencsath, U.S. Food and Drug Administration, Gulf Coast Seafood Laboratory, Dauphin Island, AL
Susan McCarthy, U.S. Food and Drug Administration, Gulf Coast Seafood Laboratory, Dauphin Island, AL
Ronald A. Benner, Jr, U.S. Food and Drug Administration, Gulf Coast Seafood Laboratory, Dauphin Island, AL
Introduction: Precooking of tuna is a potential critical control point (CCP) in commercial manufacturing of canned tuna.  An understanding of the thermal properties of histamine-producing bacteria (HPB) and histidine decarboxylase (HDC) enzymes is required to effectively evaluate the utility of this CCP.  The thermal properties of HPB have been determined, but the thermal resistance of the HDC enzymes is unknown.  

Purpose: The purpose of this study was to determine the D- and z-values of selected HDC enzymes in order to evaluate the CCP of precooking during the canning process and provide scientific data to support future FDA guidelines.   

Methods: Histidine decarboxylase (hdc) genes from three strains each of Morganella morganii, Enterobacter aerogenes, Raoultella planticola, and Photobacterium damselae were cloned, expressed, and purified using the Champion pET Directional TOPO Expression System, pET100 cloning vector, and HisPur Cobalt resin.  The heat resistance of all enzymes was compared at 50°C, and the D- and z-values from one strain of each HPB were determined from 50-60°C.  To evaluate heat inactivation during canned tuna processing, tuna tissue was inoculated with HDCs and heated to 60°C.

Results: There was no statistical difference in D-values at 50°C within HPB species (P=0.061-0.117).  The HDC from E. aerogenes had the highest D-value at all temperatures.  The ranges of D-values for the HDC enzymes from M. morganii, E. aerogenes, R. planticola, and P. damselae were 1.6-4.1, 1.6-6.3, 1.9-4.3, and 1.6-2.9 min at temperatures ranging from 50-60°C, respectively.  The z-values for M. morganii, E. aerogenes, R. planticola, and P. damselae were 19.2, 18.0, 22.0, and 13.3 min, respectively.  The HDCs from all HPB except E. aerogenes showed no significant activity after heat treatment to 60°C. 

Significance: The data generated in this study will help refine current guidelines for thermal destruction of the HDC enzyme.

Back to: Poster Session 1 – Produce, Meat, Poultry and Eggs, Non-microbial Food Safety; Laboratory and Detection Methods; Communication Outreach and Education; Seafood; Antimicrobials; Food Toxicology
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