凍結乾燥食品のコラプス防止のための電気容量変化を用いた氷結率の設定 <技術論文>

Control of ice fraction by capacitance measurement for prevention of collapse during freeze drying of food

Tohi Sadao

Hagura Yoshio

Suzuki Kanichi

日本食品科学工学会誌

We evaluated a non-destructive determination for preventing collapse (foaming and shrinking phenomena through evaporation to dryness) in freeze-dried food products. Three different types of miso (soy-bean paste) soup prepared with different contents on a dry solid basis were used as the food product model. Differential Scanning Calorimetry (DSC) determination was used to evaluate the freezing ratio of the miso soup. The soup was freeze-dried to evaluate the relationship between the incident of collapse and the freezing ratio. We found that collapse was completely prevented when the freezing ratio was about 95% or greater. At any solid content of the soup collapse was also prevented when the freezing ratio was 95% or greater. Freeze-dried temperature of the miso soup was changed to determine the capacitance variation, and its relationship with the incidences of collapse was evaluated. The result revealed that the incidence of collapse was about 50% at a temperature where capacitance was maximal. Additionally, capacitance of the soup was graphically differentiated, and we found that the incidence of collapse was 0% at freezing temperatures lower than the inflection point where the soup exhibited a freezing ratio of 95%. These results suggested that in preparing freeze-dried food products, collapse during freeze-drying could be prevented by continuously monitoring the capacitance of food products during freezing process, and by freezing them to a temperature at which collapse can be suppressed.

凍結乾燥食品のコラプス(蒸発乾燥による発泡・収縮現象)発生を防止するための非破壊測定法を検討した. コラプスの発生は, 凍結乾燥前工程(凍結工程)での凍結不足が主な要因である. 食品のモデルとして固形分含有量が異なる3種類の味噌汁を用いた. まず, 味噌汁の氷結率をDSC測定により調べ, さらに味噌汁を凍結乾燥し, コラプス発生率と氷結率との関係を検討した. その結果, 氷結率が約95%以上でコラプスの発生が抑えられることが明らかとなった. 味噌汁の固形分含有量を変えた場合も同様に氷結率が95%以上でコラプスの発生が抑えられた. 次に, 味噌汁の凍結温度を変えて電気容量を測定し, コラプス発生率との関係を検討した. その結果, 電気容量が極大値を示す温度でコラプス発生率が約50%となった. 電気容量変化とコラプス発生率との間には何らかの関係があることから, 電気容量変化からコラプス発生を予測できる可能性が示唆された. さらに, 味噌汁の電気容量変化のグラフを図微分すると, 低温側の変曲点以下の凍結温度範囲ではコラプス発生率が0%になることがわかり, このとき, 味噌汁の氷結率が95%に達していることが明らかとなった. 以上の結果から, 凍結乾燥食品の製造において, 凍結過程の食品の電気容量を連続で測定し, コラプスの発生を抑制できる温度まで冷却することにより, 凍結乾燥過程のコラプス発生を防止できる可能性が示唆された.

Domestic arts and sciences [ 590 ]

jpn

日本食品科学工学会

[ISSN] 1341-027X

[NCID] AN10467499

[URI] http://www.journalarchive.jst.go.jp/japanese/jnlabstract_ja.php?cdjournal=nskkk1995&cdvol=50&noissue=8&startpage=356