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Exploring Quality Changes of Fresh Asparagus when Preserved Unfrozen at Subzero Temperature Using the Supercooling Technology

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Title:Exploring Quality Changes of Fresh Asparagus when Preserved Unfrozen at Subzero Temperature Using the Supercooling Technology
Authors:Li, Muci
Contributors:Jun, Soojin (advisor)
Food Science (department)
Keywords:Food science
Food Preservation
Date Issued:Dec 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:Food waste is becoming a more and more critical problem in the United States. One of the methods to solve the food waste problem is cold storage for an enhanced shelf life of perishable food. However, when food is stored under cold storage conditions, there may also be some adverse changes of food quality, which can result in undesired degradation of alterations in odor, color, texture, and other quality factors. Although refrigeration storage can maintain the quality of perishable food for a longer period, the storage time and viable quality of food materials are still limited. On the other hand, although freezing storage can provide an extended preserving period for food, some food may lose their texture characteristic after freezing and thawing treatment. Therefore, it is beneficial to develop a technology for storage of fresh perishable food in order to increase the preservation period.
Supercooling refers to the state that the matrix without ice nucleation below its freezing point, which also has several names such as subcooling and undercooling. Since there is notice crystallization, quality degradation due to its freezing and thawing treatment can be excluded to maintain food fresh.
In this study, a supercooling technique combining oscillating magnetic field (OMF) and pulsed electric field (PEF) was applied to preserve asparagus, and the quality parameters before and after the storage were analyzed to determine the capability of supercooling technology for an enhanced preservation method of foods. The asparagus was chosen as a test sample because it is popular among consumers and perishable. In the study, 50 g asparagus samples (about 7 to 8 spears) were preserved in its supercooled state (-3ºC) at an ambient temperature of -6ºC for 2 weeks. The PEF was delivered to the samples via side electrodes made with titanium foils and the input voltage and frequency of PEF are 20 V and 20 kHz, respectively. Two electromagnets made with copper wire was set in the supercooling chamber to provide oscillating field and the voltage and frequency used for the OMF was 60 V and 1 Hz, respectively. After the treatment, the quality parameters of asparagus samples were measured and compared with controlled sample stored in refrigeration and freezing conditions. The quality parameters included color, drip loss, texture, chlorophyll, anthocyanin and enzymatic activities (superoxide dismutase (SOD) and catalase (CAT)). The results claimed that refrigeration storage made significant color changes for asparagus samples in 14-day storage, while the supercooling technique has a better ability in maintaining the color of samples. Furthermore, texture changes found in refrigerated samples were not found in supercooled samples, either. It was claimed that supercooling technique combined with PEF and OMF emission had the potential for improved preservation over refrigeration of samples without the damaging effects of ice formation and growth during freezing. Compared with refrigerated samples, supercooled samples had a higher chlorophyll content and lower anthocyanin contents, which kept samples fresher and maintained the enhanced qualities. After 14-day storage, SOD activities of supercooled and frozen samples were significantly higher than refrigerated samples, which showed supercooling technique process could significantly increase the activities of SOD and inhibit the increase of relative conductivity.
The results showed that supercooling technique combined with PEF and OMF could be applied on asparagus preservation for maintaining its quality for a longer period. As for color and texture, the supercooling technique had advantaged over refrigeration. Future works could address testing of diverse fresh produce using the developed supercooling technique. Furthermore, the supercooling temperature was approximately 2ºC below the equilibrium freezing temperature of the food sample in the study, and further study could focus on decreasing of supercooling temperature for an enhanced storage condition.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
Pages/Duration:72 pages
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Food Science

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