Melting Point Measurement of Edible Fats and Oils Using Electric Capacity

電気容量測定により油脂の融点測定を試みた. 油脂試料として, オリーブ油, ダイズ油, ナタネ油, ピーナツ油, トウモロコシ油, ゴマ油, トリオレインを使用した. 油脂試料の融解に伴う電気容量変化をキャパシタンスメータを使用して, -160～30℃の範囲で測定した. また, DSCを使用して油脂試料の融解に伴う熱量変化を-160～30℃の範囲で測定した. 油脂試料の電気容量は温度の上昇と供に大きくなった. 電気容量の温度依存性を表す曲線は, 全ての油脂において類似した形状であったが, 曲線の変曲点は, 油脂ごとに異なっていた. また, 油脂の融点付近において電気容量の変化が顕著であった. 温度変化に対する電気容量の変化を温度の増分で微分し, 電気容量の一次微分曲線を作成した. 電気容量の一次微分曲線とDSC曲線との間には類似性が見られた. 電気容量の一次微分曲線とDSC曲線からそれぞれ, 融解開始温度, 融解ピーク温度, 融解終了温度を読み取った. 電気容量測定により得られた融解温度はDSC測定により得られた融解温度と良好に一致していた. 電気容量測定により, 油脂の融点測定が可能であることが示唆された.Determination of the melting temperature of fats and oils was attempted by measuring electric capacity (capacitance). Olive oil, soybean oil, rapeseed oil, peanut oil, corn oil, sesame oil and triolein were used as samples. Capacitance change with melting of samples was measured in the temperature range, -160~30°C using a capacitance meter. Differential scanning calorimetry (DSC) was also used to examine the enthalpy change accompanying the melting. The capacitance of the fat and oil samples increased with increasing temperature. The temperature dependency curve of capacitance of each sample had a unique inflection point, though similar in its shape in all samples. The change in capacitance was remarkable around the melting point of each sample. The change in capacitance corresponding to temperature change was differentiated by the temperature increment, and the first derivative curve of capacitance thus obtained was quite similar to the DSC curve. Initial, peak and end temperatures of melting were read from the first derivative curve of capacitance and the DSC curve. These melting temperatures obtained from the capacitance measurement was consistent with those from DSC, thus suggesting that the melting temperatures of fats and oils can be determined accurately by measuring capacitance