Produce Degradation Pathways and Prevention

Produce Color and Appearance 199

“Meso” compounds: derivatives in which the C-2 vinyl group has been

reduced to to ethyl

“Pyro” compounds: derivatives in which the C-10 carbomethoxy group has

been replaced by hydrogen

Chlorins e: derivatives of pheophorbide resulting from cleavage of the iso-

cyclic ring

Rhodins g: the corresponding derivatives from pheophorbide b

7.3.2 DEGRADATION OF CHLOROPHYLLS DURING SENESCENCE,

STORAGE, AND PROCESSING

The past research on chlorophylls related to fruits and vegetables is available in
reviews and monographs (Simpson, 1985; Schwartz and Lorenzo, 1990; Gross,
1991).
The senescence process of chlorophyll is not yet fully understood. Its maximum
concentration, which occurs in the summer, decreases stepwise until it totally dis-
appears in the autumn. The degradation of chlorophyll a proceeds faster than that
of chlorophyll b. Pheophytin and pheophorbide are the initial degradation products.
Oxidation of the ring structure leads to formation of chlorines, followed by formation
of colorless products (Gross, 1987). Amir-Shapira et al. (1987) investigated chloro-
phyll changes during senescence in citrus peel and parsley leaves. Chlorophyllide a

FIGURE 7.3Chlorophyll.

NN

NN

Mg

CH 2

H

COCH 3

H

CH 3

C H R

CH 2

CH 3

H

CH 3

O

H

H 3 C

H

C

H

CH 2

CO 2

1

2 3

4

5

7 6

8

10

CH 3 CH 3

H H

H

H

chl a, R= -CH 3

chl b, R = -CHO