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Acoustic Energy as a Practical Juice Safety Intervention for Inactivation of Acid Tolerant Pathogenic Microorganisms

Feng, Hao
University of Illinois - Urbana-Champaign
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The long-term goal of the proposed research is to develop a novel and practical food safety intervention, manothermosonication (MTS), to pasteurize fruit and vegetable juices to achieve a 5-log reduction and at the same time to maintain product quality. This proposal requests funding for a three-year period to implement the following specific objectives:
  1. To develop a variable frequency (MMM) manothermosonication (MTS) experimental prototype with maximized cavitation to facilitate pasteurization of fruit and vegetable juices;
  2. To evaluate the efficacy of MMM and single frequency ultrasound technique on inactivation of acid tolerant Escherichia coli K-12 and Salmonella spp. in apple and orange juices, and to study the inactivation kinetics;
  3. To examine the sublethal injury of acid tolerant pathogens after MTS treatment, the acid tolerance of injured cells, and survival of injured cells during storage at 4 and 22 degrees C;
  4. To study the MTS inactivation mechanisms by characterizing cavitation activity in an MTS treatment chamber, and by examining cell damage using scanning electron microscopy and fluorescence staining techniques;
  5. To compare quality attributes of MTS-processed apple and orange juice samples to counterparts processed with a thermal pasteurization method;
  6. To determine the energy requirement of an MTS process compared to thermal pasteurization to achieve the same level of microbial destruction.
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NON-TECHNICAL SUMMARY: Consumers' need for safe, fresh, and nutritious foods continues to stimulate the development of novel food safety concepts. In this proposed study, by exploring the efficacy of a novel concept, the combination of mild heat, low pressure, and acoustic energy using a multiple frequency technique, we will acquire important knowledge about the interaction between acoustic energy and bacteria, and the potential use of this new technology in food safety applications.

APPROACH: In this proposed study, by testing the efficacy of a novel concept, multifrequency, multimode, and modulated (MMM) manothermosonication (MST), we will mainly explore the technical feasibility of this technology as a juice safety intervention. The inactivation kinetics of MMM+MST will first be studied with optimal operation conditions determined by measuring the cavitation activity. The quality of the product processed with MMM+MST will be compared with counterparts treated with traditional pasteurization technologies. Two model food systems used in this study include apple juice and orange juice. Target microorganisms that will be tested are Escherichia coli K-12 and Salmonella spp. The sublethal injury of the cells, as well as the inactivation mechanisms will also be studied.

PROGRESS: 2007/09 TO 2008/09
OUTPUTS: The responses of Escherichia coli K12 to four types of ultrasonic treatments (sonication, manosonication (MS), thermosonication (TS), and manothermosonication (MTS)) were investigated at 40, 47, 54, 61 degrres C and 100, 300, 400, 500 kPa, in comparison with heat only treatments at the same temperatures. The effect of pH on inactivation of E. coli K12 by sonication at 0 kPa/40 degrees C, MS at 300 kPa/40 degrees C, TS at 0 kPa/61 degrres C, and MTS at 300 kPa/61 degrees C was also investigated. The inactivation kinetics were evaluated with five selected models and two statistical indices. Within the time frame (4 minutes) and temperature range used in this study, inactivation of E. coli K12 with a single lethal factor (heat or sonication) can be described by a first-order kinetic equation. For treatments with more than one lethal factor, non-linear inactivation curves were observed. Based on visual inspections, the non-linear survival curves of E. coli K12 cells were featured by a fast initial inactivation followed by a slow reduction in microbial survival counts. The biphasic model produced the best fit of the inactivation data compared to other non-linear models. Environmental scanning electron microscopy images showed extensive cell damage and breakage on E. coli K12 cells treated by MS, TS, and MTS. At all pH levels, the inactivation rates of E. coli K12 in a buffer by TS and MTS were significantly higher than those by sonication and MS. A 5-log reduction of E. coli K12 population by TS and MTS was achieved in 0.5 and 0.25 minutes, respectively. With an initial count of 108 CFU/ml, no colonies were detected at pH 3 after a 0.25-minute MTS treatment. The lethal effect of MTS was enhanced at low pH (pH 3 and 4), whereas at non-lethal temperature of 40 degrees C, no increased killing was observed. The biphasic linear, log-logistic, and modified Gompertz kinetic models allowed better fitting of the inactivation data for MTS, TS, and MS treatments at different pH than the first order and Weibull models. The survival counts of sonication-treated E. coli K12 at all pH levels fitted well to a first-order kinetic model.

IMPACT: 2007/09 TO 2008/09
The kinetics study will provide a useful tool for finding the optimal operation conditions to reach a 5-log reduction required by USFDA. The MTS treatment may provide a promising alternative to current thermal methods for pasteurization of liquid foods.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Natural Toxins
Viruses and Prions
Bacterial Pathogens
Chemical Contaminants