Novel Sonication Method to Enhance Food Safety

NON-TECHNICAL SUMMARY: USDA\'s Economic Research Service (ERS) reported in 2000 that the estimated annual economic costs of foodborne illnesses caused by five foodborne pathogens (Campylobacter spp., Salmonella, nontyphoidal, E. coli O157:H7, E. coli, non-O157 STEC, and Listeria monocytogenes) totaled $6.9 billion. The proposed research aims at the development of a new nonthermal process method to inactivate foodborne pathogens and provide food manufacturers with a new alternative food safety technology. <P>

APPROACH: Resonant Macrosonic Synthesis (RMS) is a new technique that can create high amplitude sound waves inside a resonant cavity. RMS can produce sound energy intensity hundreds of times higher than that can be achieved with conventional ultrasound generators. This makes RMS a potential alternative in inactivation and control of pathogenic microbes in foods. In this research, a lab-scale RMS apparatus will be developed in cooperation with the inventor of the technique to pasteurize liquid foods. The flow rate of the liquid, the inlet and outlet temperatures, and the sound power intensity will be monitored. In the experimental studies, we will use soymilk and apple cider as model foods. Listeria monocytogenes and Escherichia coli will be inoculated in the liquid foods. The RMS treatment parameters considered will include treatment time, power intensity, and product initial temperature. The kinetics of microbial reduction under RMS treatment will be studied. The D-value at different power intensities will first be determined. z(P) value, with P the sound energy intensity, will also be estimated from experimental results. An appropriate survival model will be proposed. Comparisons will be made with control, as well as with samples treated with conventional power ultrasound probes. The combination of RMS treatment with other preservation processes such as temperature and mild pressure will be explored to examine the synergistic effects. The optimal operating conditions to achieve specified microbial population reduction will be determined at the lab scale RMS apparatus. In a separate test, the effect of RMS treatment on the quality of the liquid foods will be examined. This will include color change, aroma retention, and nutrient degradation.
<P>
PROGRESS: 2001/10 TO 2006/09<BR>
Acoustic energy density and its role in a high intensity ultrasound (HIU) treatment was first examined. Studies in the 1940\'s reported very low killing rates when applying HIU to inactivate pathogens that stereotyped HIU as an ineffective tool in microbial inactivation. We found that previous HIU testing used very low energy densities (0.1 Watt/milliliter) due to the hardware limitation at that time. Experiments using much higher energy levels were conducted in the inactivation of Shigella boydii 18 IDPH. Five log cycles (99.999% killing) reduction in the population of Shigella, a benchmark required by the U.S. Food and Drug Administration for pasteurization, was achieved in 11 minutes when the energy level was 1.4 Watt/milliliter. The findings confirmed the importance of energy level in a HIU treatment. The most important was that, although further increasing the energy level could shorten the treatment time to less than one minute, the energy level needed for such a treatment (about 4 Watt/milliliter) is impossible to achieve with current HIU generation techniques. The combination of heat with HIU has thus been explored as a possible means of enhancing the efficacy of a HIU treatment. In thermo-sonication (TS) tests, we have shown that the inactivation rate of a pectin enzyme at 61C was increased by 288 fold compared to a treatment using only heat at the same temperature. A clear increase in the inactivation rate of foodborne pathogens has also been observed in E. coli and Listeria monocytogenes tests. In TS tests, we made a novel observation that there existed an upper temperature limit for TS inactivation of bacteria. Inactivation of the bacteria with HIU above this temperature would not result in any additional killing. These studies indicated the limitation of TS and the need to further enhance the efficacy of a HIU treatment at elevated temperatures. To overcome the limitation of TS, we developed a laboratory scale continuous mano-thermo-sonication (MTS) liquid food processing system and reduced the enzyme inactivation time from several minutes for TS to 30 seconds in tests to ensure the stability of orange juice. Five log cycles (99.999% killing) reduction in the population E coli K12 was achieved in 30 seconds.
<P>
IMPACT: 2001/10 TO 2006/09<BR>
The mano-thermo-sonication treatment (MTS) effectively reduced pectin enzyme activity. It also achieved an over 5-log reduction in the population of E. coli K12. It demonstrated that the MTS treatment can achieve duel inactivation of both quality degradation enzymes and pathogenic microorganisms, and thereby is a promising alternative to current liquid food processing methods. Since MTS uses mild treatment conditions compared to traditional thermal processing methods, the food processed with MTS will have an improved quality.