Abstract:

The fresh stems of Cichorium intybus L. were blanched and then shade-dried under indoor conditions. Three
blanching treatments including water bath heating, steaming and microwave heating were evaluated for inactivating
polyphenol oxidase (PPO) and increasing chlorogenic acid content in the dried leaves. The PPO activity was assayed
immediately after each blanching treatment and the chlorogenic acid content was determined after subsequent drying.
Moreover, the correlation between both parameters was analyzed and their changes during direct drying of the stems
without pre-blanching treatment were examined. The results showed that the relative activity of PPO remained at more
than 20.02% of the original level during the air drying process. All water bathing, steaming and microwave blanching
could inhibit the PPO activity effectively, which was significantly negatively correlated with the chlorogenic acid content
(P < 0.05). The highest chlorogenic acid content in dried stems was obtained by microwave blanching and then drying,
followed in decreasing order by steaming and then drying, water bathing and then drying, and direct drying. The dried
stems with microwave (600 W) blanching for 4.67 min had the highest content (8.11 mg/g) of chlorogenic acid, indicating a
16.82% decrease compared to the fresh stems and a 2.17-fold increase over that of the directly dried stems.

Key words: Cichorium intybus L., stem, polyphenol oxidase, inactivation, chlorogenic acid