A Relationship Between Weight and Capacitance Changes during Freeze-drying Process of Food

凍結乾燥機内の食品の乾燥状態(重量変化)の非破壊測定法を検討した. 食品のモデルとして10%デキストリン水溶液を用いた. まず始めに, 食品を凍結乾燥したときの重量変化と温度変化を同時に測定して, 温度測定の有効性を検討した. 次に, 凍結乾燥機内の加熱用のステンレススチール製棚板2枚を電極板として利用して, 凍結乾燥過程における食品の電気容量変化を測定した. その結果, 凍結乾燥中の食品の温度変化は, 温度センサーの設置場所によって異なり, 正確に乾燥状態を表していないことが明らかとなった. また, 電気容量変化と重量変化との間には, 良好な相関関係があった. 凍結乾燥過程における食品の電気容量を測定することにより, 凍結乾燥機内の食品の乾燥状態を把握できる可能性が示唆された.The development of a non-destructive method was attempted for the measurement of food weight change (i.e. moisture content change) in a freeze-dryer. An aqueous solution of 10% dextrin was used as a food sample. Changes in both weight and temperature of the sample were simultaneously measured during a freeze-drying process. The capacitance of sample was also measured using two stainless steel heating shelf boards as a pair of electrode plates. Sample temperature histories varied with the sample position in the dryer. Sample temperature did not precisely indicate the freeze-drying state of the sample. Determining the endpoint of freeze-drying based solely on the results of sample temperature measurements remained practical problems. The capacitance change showed a good correlation with the weight change. Thus, it is feasible to monitor the weight of a sample during freeze-drying by measuring its capacitance