Microbial Safety in Radio‐frequency Processing of Packaged Foods

Abstract

Thermal resistance of Clostridium sporogenes (PA 3679) was determined at 115.6°C, 118.3°C, and 121.1°C (240°F, 245°F, and 250°F, respectively) in phosphate buffer (pH 7.0) and mashed potatoes (pH 6.3) using aluminum thermal-death-time (TDT) tubes developed at Washington State Univ. D-values were 1.8, 1.1, and 0.62 min in phosphate buffer and 2.2, 1.1, and 0.61 min in mashed potatoes at 115.6°C, 118.3°C, and 121.1°C, respectively. Z-values were 12°C and 10°C in phosphate buffer and mashed potatoes, respectively. The thermal inactivation kinetic results were then used to validate a novel thermal process based on 27.12 MHz radio frequency (RF) energy. Trays of mashed potatoes inoculated with PA 3679 were subjected to 3 processing levels: target process (F 0~4 .3), under-target process (F 0~2 .4), and over-target process (F 0~7 . 3). The microbial challenge test data showed that microbial destruction from the RF process agreed with the calculated sterilization values. This study suggests that thermal processes based on RF energy can produce safe and shelf-stable packaged foods.

Performance evaluation of aluminum test cell designed for determining the heat resistance of bacterial spores in foods

“…The results indicate that the temperature at the center of the test cell reached within 0.5 °C of 121 °C after 60 s of heating and within 0.2 °C of 121 °C after 80 s of heating. Experimentally measured CUT for the mashed potato in the test cell was 65 s, which was approximately half of the CUT for the aluminum TDT tubes (Luechapattanaporn et al, 2004). Although the test cell CUT time was still larger than the typical D-value of the microorganisms, but for given sample volume of the solids, the CUT was reasonably short.…”

“…The 2 mm cylindrical gap between the tube's inner wall and solid bar provided a holding capacity of up to 3 ml. The sample CUT was about 2.5 min when heated in an oil bath at 121 o C. Detailed information on the design of this aluminum TDT tube can be found in Luechapattanaporn et al (2004). For the capillary tube method, a 25 µl phosphate buffer solution (pH 7.0) or mashed potato (0.25 g ± 0.05) inoculated with C. sporogenes spores at ~10 6 CFU/ml was carefully injected into the tubes, as described earlier.…”

“…Thermoresistometers are specialized and expensive, hence available in only a few laboratories worldwide. Recently, Luechapattanaporn, Wang, Wang, Tang & Hallberg (2004) described a novel aluminum tube for evaluating the heat resistance of bacterial spores in semi-solid and solid foods at sterilization temperatures. A major drawback of this aluminum tube was a long CUT of about 2.5 min, which may have compromised the accuracy of the test results.…”

Radiofrequency pasteurization of inoculated ground beef homogenate

“…Several studies (Guo et al, 2006;Luechapattanaporn et al, 2004Luechapattanaporn et al, , 2005Nagaraj et al, 2015;Zhao, Flugstad, Kolbe, Park and Wells, 2000) have evaluated the effectiveness of RF heating on pasteurizing sausage (Houben, Schoenmakers, Van Putten, Van Roon and Krol, 1991); cured hams (Bengtsson, Green and Valle, 1970;Orsat, Bai, & Raghavan, 1999); and skinless meatloaf (Zhao et al, 2000); sterilizing inoculated mashed potatoes and scrambled eggs with Clostridium sporogenes (PA 3679) (Luechapattanaporn et al, 2004(Luechapattanaporn et al, , 2005 and achieved sufficient microbial inactivation while producing foods with a higher quality than conventionally treated products.…”

Optimization and evaluation of heat-shock condition for spore enumeration being used in thermal-process verification: Differential responses of spores and vegetative cells of Clostridium sporogenes to heat shock

“…In general, the viable spores of C. sporogenes are counted after subjecting samples to a heatshock (or heat-activation) treatment, i.e., a condition of 90 o C for 10 min used in other studies validating thermal sterilization processes (6,7), and conventional conditions of 70 o C for 30 min (8,9) and of 80 o C for 20 min (10)(11)(12); the spores are used in the unheated controls in these studies and not the samples that are heated. Any of the cited combinations are believed to be sufficient to activate spores and to inactivate vegetative cells of any strains tested.…”