NOVEL FREEZING TECHNIQUE USING COMBINED PULSED ELECTRIC AND MAGNETIC FIELDS TO MAINTAIN THE QUALITIES OF FRESH FRUITS AND VEGETABLES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: AFRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 1001343
• Grant No.: 2014-67017-21650
• Cumulative Award Amt.: $475,370.00
• Proposal No.: 2013-03842
• Project Start Date: Dec 1, 2013
• Project End Date: Nov 30, 2017
• Grant Year: 2014
• Program Code: [A1361]- Improving Food Quality

Recipient Organization
UNIV OF HAWAII
3190 MAILE WAY
HONOLULU,HI 96822

Performing Department
HNFAS

Non Technical Summary
The key objectives of this proposal are to (1) design and optimize the freezing chamber featured with combined pulsed electric and magnetic fields and (2) test and validate the control of the nucleation and growth of ice crystals in targeted fresh fruits and vegetables. Conventional freezing methods are used to retain the quality of food products over long storage periods. However, irreversible destruction of food tissue structures due to ice crystallization during freezing, i.e. freeze crack and drip loss from cryogenic freezing, remains a significant problem on the quality control for frozen fruits and vegetables. Thereby, we hypothesize (1) that the pulsed electric field would cause water molecules to be polarized and re-aligned, and oscillating magnetic waves would enhance the rearrangement of water molecules by diamagnetism of water molecules and (2) combined pulsed electric and magnetic fields would lead to a significant delay of ice nucleation at subzero temperatures, and finest ice crystallization in food matrix, resulting in full retention of food qualities. The emerging combination freezing technology will extend the freshness of targeted produce by inhibiting the ice crystal growth without the use of chemicals, and achieving rapid uniformity of temperature distribution within food tissues. The proposed technology can impact a majority of food industries and business sectors to deal with raw and frozen food products, i.e. fruits, vegetables, grains, meats, and dairy products, by extension.

Animal Health Component

40%

Research Effort Categories

Basic

20%

Applied

40%

Developmental

40%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
501	5010	2020	100%

Knowledge Area
501 - New and Improved Food Processing Technologies;

Subject Of Investigation
5010 - Food;

Field Of Science
2020 - Engineering;

Keywords

electric field

flavor retention

fresh produce

magnetic field

quick freezing

supercooling

Goals / Objectives
Project Goal: To preserve the original freshness of produce by controlling ice crystallization at subzero temperatures using combined pulsed electric and magnetic fields. Project Objectives: Objective 1: Design the proposed freezing chamber and optimize the operating parameters to decelerate the nucleation and growth of ice crystals in targeted fresh produce. Objective 2: Explore the mechanism of combined pulsed electric and magnetic fields on freezing process. Objective 3: Develop and validate the ice crystallization model under pulsed electric and magnetic fields at molecular levels. Objective 4: Test physiochemical properties of food samples as impacts of the proposed freezing technique. Objective 5: Organize and host annual project director's meetings for the USDA/NIFA-AFRI Improving Food Quality and Function and Efficacy of Nutrients programs. The primary activities will include dissemination and share of information, accomplishments and progress made through programs, development of a rapport with NIFA staffs, and discussion about the direction of food science research, education, and extension.

Project Methods
Task 1. Develop a novel freezing chamber equipped with a combination of pulsed electric and magnetic fields. (Objective 1) The freezing chamber with a proposed combination of independent units for generation of electric and magnetic forces will be composed of rectangular plates, a wall plate, electrodes, and magnet units. The main body will have a double wall structure comprising of freezing chamber walls, which define the inner-chamber space, and outer walls that surround the chamber walls at a distance to define an outer portion. Heat insulators, which are not shown, are arranged between the outer walls and the freezing chamber walls in order to enhance the cooling efficiency inside the chamber. A rack is located in the center of the chamber for pans where food products will be placed. Magnetic field units are installed on the top and bottom of the freezing chamber. An oscillating magnetic field (OMF) generator with an electromagnetic coil is aimed to apply an oscillating magnetic field to the central portion of the freezing chamber. Other key unit is an electric field module where food products will be placed under the influence of external electric field strength between the two electrodes. The electric field generator involves electrode plates that are arranged above each pan of the rack. The electrode plates are arranged in parallel direction so that the direction of the electric field is inverted periodically. The electric field is applied to the produce which is located in the space between the plates. The developed freezing chamber will be housed in a walk-in freezer located at Dr. Jun's research lab. Task 2. Test and optimize the operating parameters (field strength and orientation, frequency, and degree of supercooling) for control of ice crystallization in food samples. (Objective 1) The samples (pure water, strawberry and potato) will be placed on the shelves of the developed freezing chamber and the temperature will be recorded using thermocouples connected to a data acquisition system (34970A, Agilent Technologies). At selected freezing temperatures, the operating parameters (field strength and orientation, frequency and supercooling) will be tested for two key purposes: (1) to delay the phase transition so that water can be unfrozen at subzero temperatures, i.e. -10 degC (ice nucleation) and (2) to make the sizes of ice crystals smaller and uniform (ice crystal growth). Field strength, working frequency, pulses, air flow characteristics, treatment time and system schematics (i.e. electrode configurations and installation of magnetic field elements) will be tested. Basic 0.9% NaCl solution samples will be used to characterize the PEF treatment for control of ice nucleation and growth. The estimated field strength in need is 250 V/m Task 3. Explore transient changes in the structure of ice crystals and food samples (strawberry and potato). (Objective 2) In order to investigate the ice morphology at a microscopic level, a unique microscope stage device will be constructed. The measurement cell can be used to study the in situ effects of pulsed electric and magnetic fields treatment under controlled temperature conditions. It is principally composed of (i) a cold stage under different treatment, (ii) a temperature control system, and (iii) an optical and recording system. Every procedure will be conducted in a walk-in freezer to ensure a perfect cold condition with a standard knife blade that will be previously stored at the same freezer temperature. Fabricated cells will be observed with a microscope fitted with a digital camera. A direct technique will be used to observe the spaces left by the ice crystals in tissue. The ice crystal morphology will be analyzed by a photonic microscopy method by reflection with episcopic coaxial lighting. The direct observation will be performed in a cold chamber maintained at -25 degC when the microtome, the microscope, the digital camera and an optical fiber providing the episcopic coaxial lighting are placed. The obtained images will be numerically stored in the computer and then analyzed by Image J (v.1.34) software that allows the estimation of the equivalent and mean particle sizes. Task 4. Develop mathematical modeling for food freezing coupled with heat and mass transfer and multiscale molecular dynamics in food samples. (Objective 3) The mechanism of deterioration of food tissues caused by frost action (freezing and thawing cycles) is related to stresses from hydraulic pressure and/or pressure of ice created by the volume increase when water transforms into ice. Regarding the internal freezing damage of food tissues, there are still issues left unaddressed, such as how ice crystals form in the complex pore structure of food tissue, where and how the cracks are created in the microstructure of tissues, and how the microstructure of food tissues responds to the decreasing temperature. All the resultant forces on each hydrated food tissue will be reflected in the 3D microstructure, generated by the connectivity of the hydrated food tissues. Local damage will occur if the local stress in the solid skeleton is high enough to the local damage criterion. The computational procedure for determining the frost damage will be designed on the 3D lattice structure by a number of calculations that include the pore structure information at the current temperature step, ?Tk, ice crystals formed at the previous temperature step, cold air penetration into the pores whose entries satisfy ice critical size and the stresses and resultant forces on the pore walls. Task 5. Evaluate changes in food properties after frozen with combined pulsed electric and magnetic fields. (Objective 4) To validate the proposed concept for improvement of food quality, an analytical method based on physical, chemical, microbiological, and sensory measurements should be evaluated. Scanning electron microscopy (SEM) analysis Electrochemical Impedance spectroscopy (EIS) analysis Property Analysis 1. Thaw drip loss 2. Texture profile analysis (TPA) 3. Antioxidant capacity and phenolic content measurement Task 6. Organize and host annual project director's meetings for the USDA/NIFA-AFRI Improving Food Quality and Function and Efficacy of Nutrients programs (Objective 5) 1. Exchange information, accomplishments and progress made on AFRI/NRI Improving Food Quality and Value, and Function and Efficacy of Nutrients Programs 2. Develop a rapport with NIFA staff responsible for grants reviews and approvals to strengthen communications 3. Provide a forum for meeting the requirements of congressional mandate in terms of progress and completion of projects in a timely manner, and the reporting tools associated with this process 4. Improve the NIFA post-award management of competitive grants and the federal management of these awards 5. Exploring the direction of food science research, education, and extension

Progress 12/01/13 to 11/30/17

Outputs
Target Audience: Nothing Reported 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?Several research teams and refrigeration and freezer manufacturers from around the world including Korea, China, and Japanhave been contacting us based on our research paper and patent. We tried to disseminate the results of this study and present to 2-3 national/international conference meetings. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The developed invention equipped with engineered PEF and OMF was engineered to vibrate water molecules in a food product even below the freezing point, without the formation of ice crystals. We proved that supercooled beef was preserved as fresh as raw beef without exercising any ice crystals at -5°C for at least 14 days (two weeks). We also tested the supercooling process on a fresh yellowfin tuna (ahi) fillet, and so far, the fish has been preserved at -4°C for eight (8) days without any deterioration or compromise in quality. As a comparison, refrigerated fish at a supermarket can only be preserved for three (3) days before spoilage occurs. Pineapple, one of typical tropical fruits very susceptible to freeze injury, was successfully supercooled with preserved freshness at -6°C for 21 days. The supercooling technique was applied to test asparagus (Asparagus officinalis, L.) for quality factor analysis. The asparagus was chosen because it is popular and is considered highly perishable. Asparagus has one-week shelf life at refrigeration condition and the goal of the study is to enhance its shelf life up to 2-3 weeks while maintaining the fresh quality factors, including chemical analysis (lignin and anthocyanin), enzyme activity analysis, color measurement, weight loss, and texture measurement. These parameters were compared with those of fresh, refrigerated and frozen asparagus. It was observed that supercooled asparagus preserved for 2 weeks did not show significant quality changes compared to fresh samples.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Her, J-Y. Kang, T., and Jun, S. 2017. Supercooling of fresh-cut honeydew melon: Effect of oscillating magnetic field (OMF). Institute of Food Technologists (Las Vegas, 2017).
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Hoptowit, R. and Jun, S. 2017. Design and fabrication of a microcontroller based supercooling control unit for use in food preservation. Institute of Food Technologists (Las Vegas, 2017).
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Kang, T., Hoptowit, R., and Jun, S. 2017. Investigation of the effect of oscillating magnetic field on fresh-cut pineapple and agar gel as a model food during supercooling preservation. Institute of Food Technologists (Las Vegas, 2017)
• Type: Theses/Dissertations Status: Published Year Published: 2017 Citation: Hoptowit, R. 2017. Design, fabrication, and validation of a microcontroller based supercooling control unit for use in food preservation. 2017. Masters dissertation, University of Hawaii.
• Type: Journal Articles Status: Submitted Year Published: 2017 Citation: Kang, T., Her, J-Y., Hoptowit, R., and Jun, S. 2017. Investigation of the effect of oscillating magnetic field on fresh-cut pineapple and agar gel as a model food during supercooling preservation. Journal of Food Science.
• Type: Journal Articles Status: Submitted Year Published: 2017 Citation: Her, J-Y., Kang, T., Hoptowit, R., and Jun, S. 2017. Supercooling of fresh-cut honeydew melon: Oscillating magnetic fields (OMFs) effect. Journal of Food Engineering.
• Type: Journal Articles Status: Submitted Year Published: 2017 Citation: Her, Y-Y., Shafel, T., and Jun, S. 2017. Effect of the subzero nonfreezing preservation on the quality of beef steak (London broil). Food Research International.

Progress 12/01/15 to 11/30/16

Outputs
Target Audience:At present, more than 20 various business sectors including local food manufacturers, retailers, and distributors show their interests in the commercialization of the supercooling technology. Home appliance manufacturers include the LG, Hair and Samsung can be our target audiences. 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?Several research teams and refrigeration and freezer manufacturers from around the world including Korea, China, and Norway have been contacting us based on our research paper and patent. We tried to disseminate the results of this study and present to 2-3 national/international conference meetings. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? An oscillating magnetic field (OMF) was used to achieve an extension of a supercooled state within honeydew melon and pineapple. At a freezer temperature of -10 °C, the internal temperature of the honeydew melon under OMF treatment was -5 °C, approximately four degrees below its freezing point during the entire testing period (approximately 21 d). The pineapple was preserved in a supercooled state at around -7 °C and the supercooling phenomenon supported with OMF was maintained for 2 weeks, whereas the untreated sample was spontaneously nucleated within 24 h. To inhibit sudden ice nucleation, the OMF treatment was controlled using a repeating sequence of on/off cycles during the entire experiment time and the time duration of each cycle was 120/420 s, respectively. The microstructures of supercooled samples were measured to estimate physical structure and properties of the cells. In addition, quality factors such as, microbiological analysis, drip loss, color, pH, titration acidity and soluble solid contents for supercooled honeydew melon samples were evaluated and compared with fresh, refrigerated (at 3 °C) and frozen (at -7 °C) samples. Although few cells in the supercooled honeydew melon samples had undulated walls compared to fresh samples, the cells were closely bonded to each other and distorted cells which caused by ice crystal formation were not found. The qualities of the supercooled honeydew melon were not significantly different from those of the fresh samples (P > 0.05). In addition, the qualities of the supercooled pineapple samples were not significantly different from those of the fresh samples after 14 d of storage (P > 0.05). Based on this study we can contribute basic process for long-term preservation of fresh-cut fruit and vegetable in the real food industry.

Publications

• Type: Journal Articles Status: Published Year Published: 2016 Citation: Mok, J.H., Her, J.Y., Kang, T., Hoptowit, R., and Jun, S. 2016. Effects of pulsed electric field (PEF) and oscillating magnetic field (OMF) combination technology on the extension of supercooling for chicken breasts. Journal of Food Engineering, 196, 2735.
• Type: Journal Articles Status: Submitted Year Published: 2016 Citation: Her, J.Y., Kang, T., Hoptowit, R., and Jun, S. 2016. Supercooling of fresh-cut honeydew melon: Oscillating magnetic field (OMF) effect. LWT-Food Science and Technology
• Type: Journal Articles Status: Submitted Year Published: 2016 Citation: Her, J.Y., Shafel, T., and Jun, S. 2016. Effect of the subzero nonfreezing preservation on Quality and shelf life of beef steak. Meat Science.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Her, J., Hoptowit, R., Kang, T., and Jun, S. 2016. Supercooling of perishable foods for extended freshness and shelf life in the cold chain. FOOMA JAPAN International Food Machinery & Technology Exhibition, June 7-10, Tokyo, Japan
• Type: Theses/Dissertations Status: Published Year Published: 2016 Citation: Shafel, T. 2016. MS dissertation, Food Science, Combination pulsed electric field and oscillating magnetic field assisted supercooling of beef and fish: a novel preservation technique.

Progress 12/01/14 to 11/30/15

Outputs
Target Audience:Local farmers and entrepreneurs to turn their raw food materials into profitable value-added food products by enhancing the shelf life. Food refrigeration and freezer manufacturers. Food distributors (adapt supercooling chain as an alternative to 'cold chain') 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?In Spring of 2015, the group was selected and trained as the second cohort of XLR8UH Proof of Concept Center funded by the Vice President of Research and Innovation (VPRI) at University of Hawaii. The focus of XLR8UH was on investing in innovative ideas and providing a launch pad for commercialization. Also The PI's group was the first UH spinout to be invited to present at the First Look LA showcase of university technologies at UCLA's California NanoSystems Institute on June 24, 2015. 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 pulsed electric field (PEF) and an oscillating magnetic field (OMF) were used to achieve an extension of a supercooled state within strawberries. At a freezer temperature of -8°C (± 1°C), the internal temperature of the strawberry under PEF and OMF treatment was -3.5°C, approximately two degrees below its freezing point during the entire testing period (approximately 4 days). The general protocol for treatment is: (i) different duty stages with different time durations for the pulsed electric fields (PEF) and (ii) an oscillating magnetic field (OMF) stage applied during the PEF duty stage to inhibit sudden ice nucleation. To ensure reliable performance of each PEF/OMF stage, an IGBT (insulated-gate bipolar transistor) based H-bridge controlled by microcontroller was fabricated. A sample chamber containing electromagnets and electrodes for PEF and OMF generation was also fabricated to simulate compartmental housing in commercial freezers. To minimize thermal-stress induced ice nucleation, a custom predictive freezer control algorithm was developed to ensure chamber temperatures remained in the tolerance of ±0.5°C. Quality assessment factors such as microstructure and drip loss for supercooled strawberry samples were evaluated and compared with samples stored at refrigeration (4°C) and at freezing (-8°C). The structure and drip loss of the supercooled and refrigerated samples were respectively non-altered. However, the cell structures of the strawberry stored at -8°C were seriously damaged. In addition, drip loss of strawberries frozen at -8°C was the highest as 10.14%, compared with supercooled and fresh strawberries.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Mok, J.H., Choi, W., Park, S.H., Lee, S.H., and Jun, S. 2015. Emerging pulsed electric field (PEF) and static magnetic field (SMF) combination technology for food freezing. International Journal of Refrigeration 50: 137-145
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Shafel, T., Lee, S.H., and Jun, S. 2015. Food preservation technology at subzero temperatures: A review. Journal of Biosystems Engineering 40(3): 261-270
• Type: Journal Articles Status: Submitted Year Published: 2016 Citation: Mok, J.H., Choi, W., and Jun, S. 2015. Effects of Pulsed Electric Field (PEF) and Oscillating Magnetic Field (OMF) Combination Technology on the Extension of Supercooling on Chicken breasts. Journal of Food Engineering
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Shafel, T., Lee, S.H., and Jun, S. 2015. Extension of Supercooled State in Beef Steak using Pulsed Electric Fields and Oscillating Magnetic Fields as a Novel Preservation Technique. The 2015 IFT Annual Meeting, July 11-14, Chicago, IL

Progress 12/01/13 to 11/30/14

Outputs
Target Audience: Local farmers and entrepreneurs to turn their raw food materials into profitable value-added food products by enhancing the shelf life Food refrigeration and freezer manufacturers Food distributors (adapt supercooling chain as an alternative to 'cold chain') 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? 1. Test a combination of pulsed electric field (PEF) and oscillating magnetic field (OMF) to achieve an extension of the supercooled state in beef steak with an internal temperature of -4.5 °C for up to two weeks. 2. Test the existence of shock-induced freezing after physical manipulation of supercooled samples confirmed by scanning electron microscopy (SEM) or other microscopic analysis.

Impacts
What was accomplished under these goals? In this study, a combination of pulsed electric field (PEF) and oscillating magnetic field (OMF) was used to achieve an extension of the supercooled state in a chicken breast stored at a freezer temperature of -7°C (± 0.5). The combined use of PEF and OMF maintains the vibrational motion of water molecules thus affectively inhibiting sudden ice nucleation. Microbial, chemical, and physical tests were applied to access quality aspects of the supercooled chicken breast. Microbial analysis of aerobic mesophilic bacteria, coliform count, and Escherichia coli K12 was carried out on each sample at times of 0, 6, 12, 18, and 24 hours during the supercooling process using procedures by AOAC. There was a decrease in the cell viability of 20% after 6-hr of supercooling with a subsequent decrease to full lethality in 18 hrs storage. No microbial recovery was observed when cold temperature shock was removed from the samples. The microstructure (Scanning electron microscopy), drip loss, texture, and lipid oxidation (FFA and TBARS) for supercooled chicken breasts were evaluated as compared with control samples. The PEF and OMF supercooling was found to maintain the fresh chicken breast qualities, thus suggesting this preservation technique may be utilized to preserve the organoleptic qualities found in fresh meats.

Publications

• Type: Journal Articles Status: Published Year Published: 2014 Citation: Mok, J.H., Choi, W., Park, S.H., Lee, S.H., and Jun, S. 2015. Emerging pulsed electric field (PEF) and static magnetic field (SMF) combination technology for food freezing. International Journal of Refrigeration (Available online)
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Shafel, T., Mok, J.H., and Jun, S. 2014. Quality factor analysis of a chicken breast maintained at an extended supercooling state. The 2014 IFT Annual Meeting, June 21-24, New Orleans, LA (030-03)
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Jun, S. 2014. Quality factor control and analysis of a chicken breast maintained at an extended supercooling state below the freezing point. The 81th Annual Meeting of Korean Society of Food Science and Technology (KoSFoST) in Gwangju, Republic of Korea, August 25  27.