Effect of high-humidity hot air impingement blanching and pulsed vacuum drying on phytochemicals content, antioxidant capacity, rehydration kinetics and ultrastructure of Thompson seedless grape

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.

Keywords:

• High-humidity hot air impingement blanching (HHAIB)
• pulsed vacuum drying (PVD)
• antioxidant capacity
• chlorophyll degradation
• transmission electron microscope (TEM)
• low field nuclear magnetic resonance (LF-NMR)

Declaration of interest

Authors declare that this manuscript is original and authors have no known conflict of interest associated with this manuscript. The results reported in this manuscript have not been influenced by any financial support. We have not excluded any individual who satisfied the authorship criteria. We confirm that all the listed authors have read and approved the content of the manuscript. The corresponding author would be the sole contact for the editorial process.

Additional information

Funding

This research was supported by the National Natural Science Foundation of China (Nos. 31772026, 31760471), the National Key Research and Development Program of China (No. 2017YFD0400905), and the basic scientific research program for public welfare scientific research institutes in Xinjiang Uygur Autonomous Region (KY2019027).