Progress 01/01/21 to 12/31/22
Outputs
Target Audience: Researchers: This project will design and build a continuous flow thermo-ultrasonic reactor with a short pasteurization time. Therefore, it will substantially advance the emerging technology of ultrasonic pasteurization of liquid foods. Consumers: The continuous flow thermo-ultrasonic reactor will retain more sensory and nutritional properties of liquid foods and thus provide consumers with high-quality, healthy foods. Food processors: The continuous flow thermo-ultrasonic reactor will considerably increase the production rate, making the process economically feasible. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
A prototype continuous flow high-intensity thermo-ultrasonic reactor was successfully built and tested. 1. Designed and built a lab-scale continuous flow thermo-ultrasonic reactor The reactor system mainly consists of three sub-systems. In the pre-treatment system, a coil heat exchanger is used to preheat the product to a selected inlet temperature. A peristaltic pump was used to transport the product to the ultrasonic reactor system. In the ultrasonic reactor system, the flow cell (key component) was designed and built. Several 3D-printed flow cells with different positions of inlet and outlet were built. By observing the flow field in the flow cells through slow-motion video, the optimal positions of the inlet and outlet were determined. The optimal height of flow cell is 18 mm which is about ¼ of the wavelength of ultrasound at 20 kHz in water. A customized ultrasonic probe with a diameter of 1 inch was used to generate a 20 kHz ultrasound. For a single reactor, experiments were performed to test the acoustic energy density (AED) and heat transfer capacity. Two flow cells were serially connected to provide the required length of processing times. In the post-treatment system, the product was cooled down to room temperature using a heat exchanger and collected in a tank. 2. Investigated effects of thermosonication on Escherichia coli, Listeria monocytogenes, and a surrogatefor psychrotrophic Clostridium botulinum spores in apple, watermelon, and carrot juices 2.1. Materials and methods 2.1.1. Juice preparation Red delicious apples, fresh seedless watermelons, and fresh whole carrots were rinsed and sanitized by soaking in 200 ppm chlorine solution for 1-2 min and then rinsed thoroughly and towel-dried. A slow juicer was used for making juice. The juice samples were filtered through a filter with a nominal opening of 150 µm. The solid content and average particle sizefor each fruit juice was 15.17%, 8.47%, and 10.0%, 78.6 µm, 26.9 µm, and 46.8 µm, respectively. 2.1.2. Bacteria preparation Freeze-dried nonpathogenic cultures of E.coli 25922, L.innocua 33090 (as a surrogate for L.monocytogents), and C.sporogenes 7955 spores (as a surrogate for C.botulinum spores) were purchased from ATCC. After rehydrating the microorganisms following the protocols, the bacteria strains were used to inoculate the juices to the bacterial density of about 108 CFU/mL. 2.1.3. Thermosonication of juices To maintain a nearly constant processing temperature (±1 °C), the maximum AEDthat can be applied was 26.2 W/(mL liquid), which was 4-12 times of those used in reported studies. This AED was applied to the sonication of the juices. The temperature for ultrasonication of each bacteria was the highest one at which about 15 s of sole heat treatment resulted in negligible microbial reduction (<1 log). Each inoculated juice was ultrasonicated for different times (from 6 s to 18 s) through changing volumetric flow rates of the juice, and a survival curvewas obtained. 2.2. Effects of thermosonication on E. coli The sonication temperature was 60 °C. For 12 s of treatment, it reached 3.71/3.82/2.43 log-reductions in apple/watermelon/carrot juices, and 4.88/3.30 log-reductions in apply/carrot juices were reached in 15 s. By fitting the Weibull model to the survival data, the estimated 5 log-reductions time for E. coli in apple, watermelon, and carrot juices was 16.0 s, 15.1 s, and 32.0 s, respectively. 2.3. Effects of thermosonication on L. innocua The sonication temperature was 61°C. For 12 s of treatment, it reached 4.14, 2.21, and 3.53 log-reductions in apple, watermelon, and carrot juices, respectively, and 6.09/4.10 log-reductions in apple/carrot juices were reached in 15 s. By fitting the Weibull model to the survival data, the estimated 5 log-reduction time in apple and carrot juices was 13.2 s and 18.5 s, respectively. The 5 log-reduction time in watermelon juice was not able to be obtained from the curve fitting because the data was so scattered, but it should be around 15 s. 2.4. Effects of thermosonication on C.sporogenes spores At 60 °C, thermosonication could not inactivate C. sporogenes spores in three juices. To the best of our knowledge, there was not a successful study in the literature that used ultrasound to inactivate bacteria spores at mild temperatures. 3. Examined effects of thermosonication on color, antioxidant activity (AA), and total phenolic content (TPC) in juices The ultrasonic treatment was performed at 60 °Cfor 12 s. The AA for untreated apple/watermelon/carrot samples were 2.75/0.31/0.53 (Trolox Equivalent (TE) mM/mL), and changed to 2.55/0.38/0.55 (TE mM/mL) after the treatment. As to the TPC, treated apple and carrot samples showed lower content of TPC (0.67/0.29 Ferulic Acid Equivalent (FAE) mg/L) than the untreated ones (0.80/0.32 FAE mg/L), whereas the TPC of watermelon samples was not significantly affected by the treatment (0.09/0.11 FAE mg/L,untreated/treated). The color for apple samples were 40.59/46.76 (L*), 1.92/11.52 (a*), and 24.95/37.56 (b*)(untreated/treated), for watermelon samples were 28.57/39.33 (L*), 20.74/30.16 (a*), and 15.74/23.66 (b*), and for carrot samples were 59.64/61.21 (L*), 42.74/45.06 (a*), and 63.88/68.73 (b*). In summary, the extremely high-intensity ultrasonic treatment did not significantly change the AA, TPC, and color in juices. 4. Tested changes in the total plate count of microorganisms (TPCM), color, AA,and TPCin thermosonicated juices during 28 d of storage at 4 °C. 1) TPCM The TPCM in untreated apple/watermelon/carrot juice on day 0 was 2.25/1.91/2.44 log CFU/mL. The untreated carrot and apple juice samples started to spoil from day 14 and 21, respectively, and the TPCM was unmeasurable because of the spoilage, while untreated watermelon juice samples did not show apparent spoilage. After the treatment, the TPCM decreased to 1.16 and 1.79 log CFU/mL for apple and carrot juice, respectively, which remained unchanged during the storage time. The TPCM in treated watermelon juice was nearly zero or below the detection limit after 28 d of storage. 2) Color The lightness (L*) of the samples barely changed (around 28.07/28.47, 20.42/27.46, 42.64/38.58 for untreated/treated apple, watermelon, and carrot samples) and significantly decreased compared with day 0 during the entire storage period. The redness (a*) of the treated apple juice samples (11.52) was significantly higher than the untreated ones (1.92) right after the treatment, but both samples had very similar a* during the rest of storage period (around 12.50/12.02 for untreated/treated samples). For watermelon samples, during the storage period, a* decreased from 30.16 to 23.41 for treated samples and increased from 20.74 to 24.98 for the untreated ones. The a* of carrot samples showed no significant changes after day 7 (around 32.43/27.83 for untreated/treated samples). The yellowness (b*) of the samples was higher on day 0 than the rest of the storage period, the color of the samples seemed to stabilize after day 0 and did not experience significant changes (around 26.32/25.11, 17.91/13.21, 43.36/42.81 for untreated/treated apple, watermelon, and carrot samples, respectively). 3) AA The AA in the juice samples decreased significantly during the storage time (from 2.75/2.55, 0.31/0.38, 0.53/0.55 TE mM/mL to 1.48/1.45, -0.09/-0.07, 0.34/-0.03 TE mM/mL for untreated/treated apple, watermelon, carrot samples, respectively). Overall, treated samples showed a slightly lower AA content compared with the untreated ones. The apple samples, both treated and untreated, showed a higher AA than the watermelon and carrot samples. 4) TPC The TPC of apple samples decreased during the storage time (from 0.80/0.67 FAE mg/L to 0.49/0.46 FAE mg/L for untreated/treated samples), and a similar trend was found for carrot samples. However, the TPC of watermelon samples were slightly increased after the storage.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Chen, G., Gao, Y., & Zhu, S. Design of an extremely high-intensity ultrasonic reactor for processing of liquid foods. Conference of Food Engineering 2022, Raleigh, NC, September 18-22,2022.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Chen, G., Gao, Y., & Zhu, S. A novel design of a batch thermosonic pasteurization process for apple juice. Innovations and Recent Development in Ultrasound Technology for Ensuring Food Safety and Quality, 2021 IFT annual meeting, Virtual. (July 2021)
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Progress 01/01/21 to 12/31/21
Outputs
Target Audience: Researchers. This project will design and build a continuous flow thermo-ultrasonic reactor with a short pasteurization time. Therefore, it will substantially advance the emerging technology of ultrasonic pasteurization of liquid foods. Consumers. The continuous flow thermo-ultrasonic reactor will retain more sensory and nutritional properties of liquid foods and thus provide consumers with high-quality, healthy foods. Food processors. The continuous flow thermo-ultrasonic reactor will considerably increase the production rate, making the process economically feasible. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?In the next reporting period, we plan to finish the following goals. 1. Investigating effects of thermosonication on Escherichia coli and Listeria monocytogenes in apple juice (pH 3.8-4), watermelon juice (pH 5.2-5.7), and carrot juice (pH 6.4-6.7) and a surrogate for psychrotrophic Clostridium botulinum spores in watermelon and carrot juices under different combinations of acoustic energy density and temperature; 2. Examining effects of thermosonication on color, antioxidant activity, and total phenolic content in the three juices; 3. Testing changes in the total plate count of microorganisms, color, antioxidant activity, and total phenolic content in thermosonicated juices during 28 d of storage at 4 °C and changes in the total plate count of microorganisms during storage under a temperature abuse condition.
Impacts
What was accomplished under these goals?
A lab-scale continuous thermo-ultrasonic reactor system was designed and built. The reactor system mainly consists of four sub-systems which are pre-treatment system, ultrasonic reactor system, post-treatment system, and cooling system. The detailed accomplishments are described below. 1. Designing and building of the pre-treatment system A jacketed vessel (Chemglass Life Sciences, 1000mL Reaction Vessel, Model No. CG193024), which connected to a Julabo F12-ED Refrigerated/Heating Circulator, was used to preheat the product to a selected inlet temperature. A stirrer (Caframo, Model No. BDC2002) was used to mix the product inside of the jacketed vessel to obtain a uniform temperature profile. A thermocouple (Omega Engineering, Model No. TJ36-CASS-040U-6) was installed to monitor the product temperature. Then a peristaltic pump (Masterflex L/S Digital Dispensing Pump System) was used to move the product from the jacketed vessel to the ultrasonic reactor system. 2. Designing and building of the ultrasonic reactor system For the ultrasonic reactor system, the key component, flow cell, was designed. Several clear 3D printed flow cells with different positions of inlet and outlet were built. By observing the flow field in the flow cells through slow-motion video, the optimal positions of the inlet and outlet were determined. The wall thickness of the flow cell was also optimized to enhance the heat transfer. Based on our recent work, the optimal height of a flow cell is 18 mm which is about ¼ of the wavelength of ultrasound at 20 kHz in water. A customized ultrasonic probe with a diameter of 1-inch (Sonics, Model No. A14101PRB20) was used to generate a 20 kHz ultrasound. For a single reactor, experiments were performed to test the ultrasonic energy and heat transfer capacity. Different product inlet temperatures (Tp, in) were applied to test the synergistic effects with ultrasound. Expected results were obtained, which confirmed that our current design meets the project requirement. Six flow cells will be serially connected, and the volumetric flow rate of the product will be adjusted to achieve a 5-log reduction of a target microorganism. Meanwhile, the flow rate of the cooling water will be adjusted to control the product outlet temperature (Tp, out) (Tp, out - Tp, in < 3 oC). 3. Designing and building of the post-treatment system For the post-treatment system, the product will be cooled down to room temperature using a heat exchanger and collected in a tank. 4. Designing and building of the cooling system Two Fisherbrand Isotemp Refrigerated/Heated Bath Circulators (Fisherbrand, Model No. 13874182, 500 W, at 20 oC) were used to provide cold water to cool down the product. Flowmeters (Omega, Model No. FP2011-RT) were connected to measure the flow rate of the cold water through the cooling vessel. Then the heat transfer between the cooling vessel and reactor can be calculated.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Chen, G. A novel design of a batch thermosonic pasteurization process for apple juice. Innovations and Recent Development in Ultrasound Technology for Ensuring Food Safety and Quality, 2021 IFT annual meeting, Virtual. (July 2021).
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