Chlorophyllide formation

Pheophorblde. Replacement of the magnesium atom In chlorophyllide with hydrogen Ions results In the formation of olive-brown pheophorblde. The degradation of chlorophyllide a and b and their respective methyl and ethyl esters In acidified acetone was studied by Schanderl et al. (10). Substitution of lower molecular weight alcohols decreased sterlc hindrance from the C-7 side chain and Increased reaction rates. Ethyl-chlorophyllide a, methyl-chlorophyllide a, and chlorophyllide reaction 1.08, 1.42, and 1.56 times faster than chlorophyll a at 55°C. The t> derivatives of all chlorophyllldes reacted approximately 5 times slower at the same temperature. Dependence of reaction rate on temperature Is nearly unaffected by length of the C-7 side chain with activation energies of 10.4, 10.6, and 10.8 Kcals/mole reported between 25°C and 55 C, respectively for the 3 reactions. 

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. 

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]. 

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