Pheophorbide, formation

The extent of the reaction converting chlorophylls into pheophytins is directly related with the temperature and the time that the blanching treatment lasts [132]. Blanching at low temperature (65°C-80°C) favors activation of the enzyme chlor-ophyllase, and thus the formation of dephytylated chlorophyll derivatives (chloro-phyllides and pheophorbides). At higher temperatures (around 100°C), the enzyme is partially inactivated, but is favored the parallel reaction of pheophytinization. The extent of chlorophyllide and pheophorbide formation will depend not only on the specific conditions of the technological treatment, but also on the level of chlorophyllase activity in the plant material [133]. 

Ziegler, R., A. Blaheta, N. Guha and B. Schonegge (1988) Enz5tmatic formation of pheophorbide and pyropheophorbide during chlorophyll degradation in a mutant of Chlorella fusca Shihira et Kraus. PL Physiol. 132, 327-32. 

Steric hindrance, attributed to the phytol chain of pheophytin, may decrease the rate of complex formation. In the study by Berezin and Koifman (20), pheophorbide a reacted 4 times faster with copper(II) ion than did pheophytin a in ethanol at 25°C. Moreover, electrostatic interaction of the C-7 propionic... 

Clydesdale and Francis (.8) attempted to Increase the amount of chlorophylllde produced in spinach during blanching in order to study its role in color retention. Blanching for 10 minutes at 155°F (68.3°C) and at a pH of 8.5 resulted in a 60% conversion of chlorophyll to chlorophylllde a. while inhibiting the formation of pheophorbide. However, the amount of chlorophylllde formed represented only 29.7% of the total pigments and decreased to 8.2% after processing at 240°F (116°C) (F0 = 4.9). None remained after 2 weeks of storage at 20°C. Spinach processed after enzyme... 

Yamauchi and Watada (1993) studied natural senescence of parsley leaves. When chlorophyll a decreased, chlorophyll a-l increased to about 3% of the content of chlorophyll a (Fig. 8.8). With storage, a small accumulation of chlorophyllide a was noted, but the accumulation did not continue nor was it retained and it did not increase to the extent of the amonnt of chlorophyll a lost. The pheophytin a content was in general low and no pheophorbides were detected leaving the formation of colomless by-prodncts as the only explanation of chlorophyll loss dnring post-harvest senescence (Heaton and Marangoni, 1996a). 

JONES I D, WHITE R c and GIBBS E (1963), Influence of blanching or brining treatments on the formation of chlorophyllides, pheophytins, and pheophorbides in green plant tissne , J Food Sci, 28, 437 39. 

While the enzyme chlorophyUase is active, some of the chlorophylls give rise to chlorophyhides. The remaming chlorophyUs have not at this stage been affected by the action of the enzyme, and are a substrate avaUable for the subsequent pheophy-tinization reaction. This takes place in parallel with the formation of pheophorbides [123]. Pyropheophytins are also detected in fermented vegetables, their presence being attributed to the heat generated in the process [142-144]. 

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