Microstructural changes in blanched, dehydrated, and rehydrated onion

Abstract

This study aims to explore the shrinkage of onion cells, single and multi-layer onion section, and expansion of intercellular pathways during dehydration. For macro and bulk-level studies, moisture analyzer and hot air convective dryer were used, respectively. Shrinkage, size retention, and color changes due to dehydration and rehydration of onion shreds were compared. At micro-level, CaCl2 and water blanched samples dehydrated at 70 °C, citric acid blanched samples dehydrated at 60 and 80 °C showed less shrinkage compared to unblanched samples. On rehydration, single layer section showed comparable cell size and intercellular space retention. Multi-layer section of CaCl2 blanched samples dehydrated at 70 °C retained better structure. At macro-level dehydration, shrinkage of CaCl2 blanched samples was the least. At bulk-level, all blanched samples shrank by 82–90%. Bulk level rehydration at 50 °C achieved better size retention. Blanching resulted a porous structure of onion shreds with an improved rehydration characteristics.