Physicochemical Characterization and Changes in Nutritional Composition of Onions Depending on Type of Freezing Process
2014
Jang, M.Y., Konkuk University, Seoul, Republic of Korea | Jo, Y.J., Konkuk University, Seoul, Republic of Korea | Hwang, I.G., National Academy of Agricultural Science, Rural Development Administration, Jeonju, Republic of Korea | Yoo, S.M., National Academy of Agricultural Science, Rural Development Administration, Jeonju, Republic of Korea | Choi, M.J., Konkuk University, Seoul, Republic of Korea | Min, S.G., Konkuk University, Seoul, Republic of Korea
Innovative freezing technology is currently applied to preserve foodstuffs for long-term storage. Generally, the quality of frozen food is closely related to the types of freezing and thawing processes. In this study, we characterized the physicochemical properties of onions depending on freezing rate. When onions were frozen at -40¡�, freezing rates were 0.1, 0.5, and 0.7¡�/min depending on air-blast quick freezer mode. Onions were thawed by microwave irradiation at 400 W. Hardness of onion dramatically decreased after freezing and thawing compared with blanched onion. However, the fastest freezing rate did not affect hardness. Thawing loss of onion decreased with a faster freezing rate. For morphological observation, onion frozen at a faster rate showed a smaller ice-crystal size. Vitamin C content decreased upon blanching or freezing, but there was no significant difference according to freezing rate. Although free sugar content also decreased upon blanching and freezing, its highest content was at 0.7¡�/min freezing. Among organic acids, malic acid content was highest at 0.7¡�/min freezing. Based on this study, it could be suggested that a faster freezing rate is effective to improve frozen food quality in accordance with preventing tissue damage or minimizing destruction of nutrients.
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