88E-21 |
Discoloration mechanism of dehydrated herbs |
T. OIKAWA1, H. Motohashi, and K. Hirasa. (1) Food Products Division/Product Development Group, Lion Corp., 3-7 Honjo 1-Chome, Sumida-Ku, Tokyo, 130-8644, Japan A beautiful green color is one of the most important qualities of dehydrated herbs. Preventing the discoloration of stored dehydrated herbs is still a big challenge, however, because the discoloration mechanisms are not understood in detail. Our objective was to study and analyze major factors causing discoloration in stored dehydrated herbs, in order to make their discoloration mechanisms clear. Non-blanched dehydrated basil and parsley samples were prepared and stored for 2 weeks under varying conditions of water activity (Aw), temperature, O2 concentration, and light intensity. Blanched dehydrated samples were also used. Discoloration was evaluated based on total visual change (TVC; L*a*b* values), chlorophyll-a decomposition rate (CHD; absorption of N,N-DMF extracts), and degree of browning (BW; absorption of 2N-NaOH extracts). For dehydrated basil, Aw and temperature significantly affected TVC, CHD, and BW, with total contribution rates, including interactions, reaching 90%. The effects of light and oxygen were significantly suppressed when Aw and temperature were <0.55 and <25C, respectively. For blanched dehydrated basil, in which enzymes were deactivated, TVC, CHD, and BW increased slightly, but less significantly than for non-blanched basil. Dehydrated parsley showed the same tendency as basil for TVC and CHD, although higher initial amounts of chlorophyll and absence of browning produced a wider range of visual change. These results suggest that discoloration can be suppressed even in the presence of light and oxygen by controlling Aw and temperature. The discoloration mechanisms of dehydrated herbs seem to vary based on the amounts of initial chlorophylls, polyphenols, and accumulated oxidants, and the activities of oxidases and chlorophyllase. Regarding chlorophyll, decomposition to phaeophorbide by chlorophyllase seems to mainly cause discoloration in dehydrated herbs, although opening of porphyrin rings by oxidases has also been reported for non-dehydrated herbs. These points require further studies.
Session 88E, Fruit & Vegetable Products: Processing
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