- 期刊
- OpenAccess
濃度對圓柱形食品冷凍乾燥速率之影響
Effect of Concentration on Freeze-Drying Rate of Cylindrical Foods
摘要
本研究採用「均一冰鋒退縮(URIF)」模式，以不同濃度的圓柱形洋菜膠試品為基本試驗材料，探討濃度對冷凍乾燥速率的影響。 實驗結果顯示試品乾燥層的水蒸汽擴散係數隨著初濃度的增加而遞減。在預冷凍溫度-60℃、乾燥室壓力12Pa、冷凝器溫度-51℃、加熱板溫度40℃條件下；初濃度1.2%～7.8%的洋菜膠試品乾燥層的水蒸汽擴散係數(m^2/s)=(-0.00744)×初濃度%+0.087179。 得到單位乾物重量洋菜膠成品所需的「乾燥時間及試品昇華面與冷凝器表面間之蒸汽壓差」隨著初濃度的增加而呈對數遞減。提高初濃度以減少初含水量，對乾燥速率的助益大於因為提高初濃度所造成乾燥層水蒸汽擴散係數降低的不利影響。液體食品冷凍乾燥，在不影響乾燥後成品品質及操作方便性原則下，應儘可能提高初濃度，以提高乾燥速率及節省製造成本。
並列摘要
The URIF (Uniformly Retreating Ice Front) model was applied in this study. This study adopted cylindrical agar samples of different concentration as basic materials to compare the effect of concentration on freeze-drying rate. The experimental results showed that water vapor diffusivity within samples was decreased with increasing initial concentration. Under prefreezing temperature. -60℃, drying chamber pressure 12Pa, condensor temperature -51℃, heating-plate temperature 40℃ and initial concentration from 1.2% to 7.8%, the water vapor diffusivities within agar samples being dried could be expressed as water vapor diffusivity (m^2/s) = (-0.00744) ) × initial concentration % + 0.087179. Required drying time and vapor pressure difference between sample's sublimation interface and condensor surface to obtain unit-weight dry agar was decreased with increasing initial concentration as logarithmic function. Increasing initial concentration to decrease water content is good for increasing drying rate, although it would also decrease water vapor diffusivity. If there are no bad influence on the quality of dried foods and the convenience of operation, freeze drying for liquid food should be tried to increase the initial concentration as high as possible for increasing the drying rate as well as decreasing the production cost.