Abstract

A new pretreatment method using high humidity hot air impingement blanching (HHAIB) followed by pulsed vacuum drying (PVD) was employed for Thompson seedless drying. The effect of this dehydration technique on phytochemicals content (ascorbic acid, total phenols and chlorophyll), antioxidant capacity (tetraethylammonium chloride, TEAC, ferric ion-reducing antioxidant power, FRAP and 2,2-diphenyl-1-picrylhydracyl, DPPH) and rehydration kinetics of Thompson seedless grape was explored. Results revealed that both HHAIB and PVD had a significant influence on phytochemicals composition and antioxidant capacity. After blanching for 150 s, the ascorbic acid and total chlorophyll content reduced by about 33% and 51%, respectively, while the total phenols and antioxidant capacity increased significantly (p ＜ 0.05). Ultrastructure observations explained why the total phenols and antioxidant capacity increased even as the ascorbic acid and total chlorophyll decreased. The findings indicate that HHAIB can enhance the total phenols content and antioxidant capacity of seedless grapes during blanching process and after drying. This information could be useful to change the general believed hypothesis that thermal processes lower the nutritional value of fruits and vegetables.

摘要

Thompson 无核干燥采用高湿热风冲击烫漂 (HHAIB) 和脉冲真空干燥 (PVD) 的新预处理方法。这种脱水技术对植物化学物质含量（抗坏血酸、总酚和叶绿素）、抗氧化能力（氯化四乙铵、TEAC、降低铁离子的抗氧化能力、FRAP 和 2,2-diphenyl-1-picrylhydracyl, DPPH）和补液的影响研究了汤普森无核葡萄的动力学。结果表明，HHAIB 和 PVD ​​对植物化学成分和抗氧化能力都有显着影响。热烫 150 s 后，抗坏血酸和总叶绿素含量分别降低约 33% 和 51%，而总酚和抗氧化能力显着提高 ( p＜ 0.05)。超微结构观察解释了为什么即使抗坏血酸和总叶绿素减少，总酚和抗氧化能力也会增加。研究结果表明，HHAIB可以提高无核葡萄在热烫过程和干燥后的总酚含量和抗氧化能力。这些信息可能有助于改变普遍认为的假设，即热加工会降低水果和蔬菜的营养价值。