Drying of ‘yacon’ pretreated by pulsed vacuum osmotic dehydration

ABSTRACT In this study, the ‘yacon’ was dried using pulsed vacuum osmotic dehydration as pretreatment followed by vacuum drying (at different temperatures) or convective drying. The use of osmotic dehydration and vacuum drying had their influence evaluated concerning drying kinetics and quality of the final product, considering fructan retention, color, and water activity. Fick’s second law and Page’s equation were suitable for the fitting of drying evolution. It was observed that higher temperatures (60 °C) resulted in shorter drying time, higher diffusivity, and higher fructan retention when compared to 40 and 50 °C. The osmotic pretreatment and the vacuum drying differed in fructan retention (p ≤ 0.05). Moreover, the dried product, osmotically pretreated, presented a shorter drying time. The best condition was vacuum drying at 60 ºC, preceded by pulsed vacuum osmotic dehydration that resulted in fructan retention of approximately 38% in a quicker, higher diffusivity and lighter color product concerning the other tested conditions.

摘要：本研究以雪莲果（yacon）为试验材料，先以脉冲真空渗透脱水（pulsed vacuum osmotic dehydration）作为预处理工序，随后分别采用不同温度下的真空干燥或对流干燥完成最终干燥。本研究评估了渗透脱水与真空干燥的应用效果，考察指标包括干燥动力学特性、最终产品的果聚糖保留率（fructan retention）、色泽与水分活度（water activity）。结果表明，菲克第二定律（Fick’s second law）与佩奇方程（Page’s equation）均可较好拟合干燥过程的变化规律。与40℃、50℃的干燥温度相比，60℃条件下干燥时长更短、物料扩散系数更高，且果聚糖保留率更优。经渗透预处理的样品与未预处理的样品，其果聚糖保留率差异具有统计学意义（p ≤ 0.05）。此外，经渗透预处理的干燥样品干燥周期更短。综合所有测试工况，最优工艺为：先实施脉冲真空渗透脱水预处理，再以60℃进行真空干燥；该工艺下产品的果聚糖保留率约为38%，且相较于其他测试组，干燥速度更快、扩散系数更高，色泽更浅。