Pathogenic E. coli inactivation in beef steaks using radiofrequency heating

Summary

Adequate cooking is one of the most effective means to eliminate foodborne pathogens from foods including Shiga toxin-producing Escherichia coli (STEC). Efficacy of radio frequency (RF) heating on inactivation of pathogens and quality studies on meat products were conducted. The steaks were inoculated with different serotypes of E. coli and packaged for RF treatment. The thickness and end point temperatures had effect on the quality of steaks and several treatments were effective in inactivating the STEC.

Situation

Meat products, particularly non-intact beef may carry a significant risk of contamination from STEC due to potential translocation of the pathogen from the skin and rumen of the carcass to the interior of the tissues during slaughter and dressing operations. Because of risks associated with consumption of contaminated beef, Escherichia coli O157:H7 as well as Escherichia coli serotypes O26, O45, O103, O111, O121 and O145 have been declared as adulterants in non-intact beef products by the United States Department of Agriculture, Food Service Inspection Service (USDA-FSIS).

Response

The effect of thickness (1.2 cm, 1.9 cm and 2.5 cm) and endpoint temperature (55°C, 65°C and 75°C) on quality of non-intact beefsteaks cooked in a RF oven was evaluated. Physicochemical characteristics were mainly affected by degree of doneness; however thickness had an effect on cooking time, heating rate, cooking and drip losses. Validation of nalidixic (Nal) acid for STEC and nonpathogenic Escherichia coli using RF heating in a model solution was conducted. Buffers were heated to three different endpoint temperatures (55°C, 60°C and 65°C). Furthermore, thermal inactivation of STEC and nonpathogenic E. coli in packaged non-intact steaks heated up to 60°C or 65°C was also carried out. A study for the USDA-FSIS cooking guidelines for mechanically tenderized product at 63°C holding at room temperature for five minutes was also performed for STEC strains.

Impact

STEC strains O157:H7, O26:H11 and O111 as well as nonpathogenic E. coli showed no significant differences compared to parent strains either before treatment or after heating therefore validating the use of Nal acid resistance as selective marker in RF studies. Results of packaged steaks indicated a log reduction of 0.99, 3.08, 2.85 and 5.02 for O157:H7, O26:H11, O111 and non-pathogenic E. coli respectively at 60°C and a 5.0 log reduction at 65°C. Validation of the protocol was effective for E. coli O157:H7 and E. coli O111 but not for E. coli O26:H11. Therefore, either adjustments to the present protocol or more heat treatment needs to be conducted for E. coli O26:H11 strains. Heating steaks to 65°C and holding at room temperature for five minutes resulted in a 5 log reduction for all strains; therefore, showing a potential validation temperature for non-intact steaks cooked with RF. The cooking protocol developed for the present study has a practical relevance for the industry since the experiments were carried on a pilot-scale RF oven and also the pathogens were tested under realistic processing conditions.

State Issue

Food Safety & Quality

Details

• Year: 2016
• Geographic Scope: Multi-State/Regional
• County: Clarke
• Program Areas:
  • Agriculture & Natural Resources