@article{oai:ir.kagoshima-u.ac.jp:00007840,
 author = {御木, 英昌},
 issue = {2},
 journal = {鹿児島大学水産学部紀要=Memoirs of Faculty of Fisheries Kagoshima University},
 month = {2016-10-28},
 note = {The thawing techniques of frozen fish have a great effect upon the quality of the thawed
fish. Therefore, in order to obtain the optimum condition to thaw the frozen fish, the relation of chemical changes in frozen fish to the temperature and time were examined, i. e., the
changes of temperature and quality by time in frozen skipjack (Katsuwonus pelamis) during
the thawing by heating from the outside were numerically calculated and compared with
experimental results.
The first, the temperature changes by time during thawing was examined. Highly accurate
values of the thermal properties (density, specific heat and heat conductivity) of unfrozen food were obtained by improved method. However, These measurements of thermal
property during freezing and thawing were difficult because of accompanying phase change
of water in food. Therefore, in order to obtain the thermal properties with phase change,
approximations on the three major components (moisture content, lipid and protein) and the
temperature were applied to calculate the heat conduction during freezing and thawing of
fishery food.
By the finite element method (FEM) introduced to solve the multi-dimensional unsteady
heat conduction equation, the thawing curves of a skipjack body (two dimensional) and a
Kamaboko (three dimensional) were simulated. The two and three dimensinal solutions were
found to agree with the measured values. Therefore, it is concluded that the pratical
approximation adopted in the numerical calculation (FEM) can explain well the actual time
change of frozen food during the freezing and thawing process.
The second, the time change of quality during thawing were examined to be predicted
based on kinetic parameters of chemical change in frozen fish, and the optimum thawing
conditions for keeping the desired freshness and color of skipjack muscles after thawing were
discussed. Organoleptic tests showed that the chemical properties such as the K-value
(nucleotide decomposition ratio) and metMb% (metmyoglobin formation percent) were good
indicators of freshness and discoloration for frozen skipjack respectively. The change with
time in the K value of muscles of mackerel (Scomber japonicus), sea bream (Evynnis japonica) and skipjack, and the metMb% of muscles of skipjack was examined at various
storage temperatures (-40~+20°C). These changes in quality were found to be expressible by the equation of first-order reaction, and the rate constant of freshness-lowering (Kf) and
rate constant of discoloration (Kc) were obtained. Since the temperature dependence of the
Kf and Kc of frozen skipjack were related by ARRHENIUS's formula, the kinetic parameters (Ea: activation energy, A: frequency factor) were obtained. Thus the rate of the change in K
value and metMb% after fluctuating temperature of frozen skipjack muscles could be
calculated from the temperature history. In this way, the hitherto recommended thawing
conditions such as a medium temperatures (about 15~20°C) and a final thawing temperature
(about -3~-5°C at center of thawed fish) were theoretically supported to be optimum for the frozen fish to be thawed by heating from the outside.
The present study made it possible to determine the optimum condition for thawing any
frozen fish evenly without deterioration its quality., 凍結魚の解凍の巧拙は解凍後の品質に重大な影響を与える。よって,解凍条件の最適化をはかるため,食品学的品質変化を温度－時間との関連でとらえ,解凍カツオを対象に外部加熱による解凍過程の品温および品質変化を数値計算でシュミレーションした。はじめに,食品の熱物性値について検討し,未凍結の場合は従来法を改良した方法により精度の高い測定値を得た。しかし,水分の相変化を伴った凍結・解凍の場合は測定が困難なため,主要三成分(水分,脂質,タンパク質)および温度の関数で求まる推算式を導き,熱物性値を得,熱伝導の数値計算に適用した。次に,相変化を伴う多次元非定常熱伝導問題の解法へ有限要素法(FEM)を導入し,カツオ魚体(2次元)およびカマボコ(3次元)における解凍曲線をシュミレーションした。その結果,実測値と良く近似した2・3次元の解が得られ,水産食品の凍結･解凍過程における熱伝導問題の解法がFEMによってより実用的なものとなった。一方,凍結カツオ筋肉のK値(ヌクレオチド分解度)およびmetMb%(メトミオグロビン生成率)の化学的特性値が鮮度および色変の指標として有用なことが官能検査から知られたので,マサバ,チダイおよびカツオのK値ならびにカツオのmetMb%の経時的変化を各種保管温度(-40°C~+20°C)について調べた。その結果,これらの品質変化を1次反応式で表わせることを見出し,各温度における鮮度低下速度定数(Kf)および色変速度定数(Kc)をそれぞれ求めた。そのために凍結カツオのKfおよびKcの温度依存性がアレニウスの式によって関係づけられるので,動力学的特性値(Ea: 活性化エネルギー, A: 頻度因子)を求めた。その結果,凍結カツオ筋肉において品温変動後のK値およびmetMb%の変化率が品温履歴から計算可能となり,従来経験的に推奨されてきた外部加熱解凍法における凍結魚の解凍媒体温度(約15~20°C)および解凍終温度(約-3~-5°C)の妥当性が理論的に裏付けられた。したがって,本研究の成果から凍結魚を均一に,しかも高品質に解凍する最適解凍条件を魚体の形状に応じて事前に設定可能となった。},
 pages = {155--266},
 title = {凍結魚の最適解凍条件に関する研究},
 volume = {33},
 year = {}
}