Kinetics of colour changes of dehydrated spinaches during storage

In order to study the relationship between chlorophyll changes and visual green colour loss in dehydrated spinaches, fresh spinaches were freeze-dried and packed after being blanched. Chlorophyll and colour loss of dehydrated spinaches were investigated for deciding their kinetics during storage at 25, 35, 45 and 55℃. The results showed that chlorophyll degradation and colour loss followed a first-order reaction. A significant relationship was found between the colour loss and chlorophyll destruction (R2＞0.95, p＜0.05) whether or not blanching prior to dehydration. The activation energies for chlorophyll degradation were determined as 39.99 kJ/mol and 41.44 kJ/mol for unblanched and blanched spinaches, respectively. For unblanched samples, the activation energies of colour loss determined on the basis of a* and h values were 18.20 kJ/mol and 44.04 kJ/mol, while those for blanched samples determined as 18.93 kJ/mol and 48.08 kJ/mol, respectively. It was highly more susceptible to chlorophyll degradation for unblanched dehydrated spinaches than blanched ones, due to lower activation energy. Blanching prior to dehydration was favorable for extending the shelf life of dehydrated spinaches. The rate constants of chlorophyll degradation, a* and h values of dehydrated spinaches were all increased with the rise of set storage temperature at the same pre-treated conditions. Storage at low temperature was good for extending the shelf life of dehydrated spinaches. The shelf life of dehydrated spinaches were 168 days (unblanched) or 465 days (blanched) during storage at 20℃.