Environmental Engineering Reference
In-Depth Information
zeaxanthin in the epilimnion, because zeaxanthin is generally a more stable com-
pound. It is photo-resistant and is found in higher contents than Chl
a
during the
summer period (Bianchi et al.
2002
; Rowan
1989
,
2000
). Photoresistance of carot-
enoids such as zeaxanthin and
ß
,
ß
-carotene involves quenching of singlet oxygen,
which prevents photooxidation reactions (Rowan
1989
; Jeffrey et al.
1997
).
5.2 Degradation of Chl
a
in Higher Plants
Degradation of Chl can have two visible effects on plant leaves (Hendry et
al.
1987
; Takamiya et al.
2000
; Matile et al.
1996
; Amir-Shapira et al.
1987
;
Merzlyak et al.
1999
; Park et al.
2007
; Pruzinská et al.
2005
; Zimmermann and
Zentgraf
2005
; Kratsch and Wise
2000
; Karuppanapandian et al.
2011
; Hillman et
al.
1994
). The first is the colour change from green to yellow or red, which natu-
rally occurs during the season change in autumn and is the most conspicuous and
rapid event. The second is cell death caused by external factors, such as injuries
sustained by low or high temperature, pathogen attack during various phases of
the life cycle of plants, and so on. It has been estimated that approximately 1.2
billion tons of Chl is degraded globally each year (Hendry et al.
1987
). The con-
versions of Chl to chlorophyllide and of pheophytin to pheophorbide in coleslaw,
cucumbers and brined olives are the result of chlorophyllase activity (Heaton et
al.
1996
). Chl
a
in crude extracts of
Chenopodium album
(white goose foot) in the
dark can produce chlorophyllide
a
, pheophorbide
a
, 13
2
-hydroxychlorophyllide
a
and pyropheophorbide
a
, the increase of which is accompanied by a concomitant
decrease in levels of Chl
a
(Shioi et al.
1991
). Chl
a
is degraded in a crude extract
of
C. album
via enzymatically catalyzed reactions (Shioi et al.
1991
).
Chl of detached rice leaves undergoes an initial long lag that lasts for one whole
day, after which it is rapidly degraded in the second and third days during experiments
conducted under total darkness at 30 °C (Okada et al.
1992
). Light only has a weak
protecting effect on soluble proteins, and ribulose-1,5-bisphosphate carboxylase/oxy-
genase rapidly disappeared under illumination with weak white light (Okada et al.
1992
). In an in vitro system of extracted broccoli florets, Chl
a
is degraded initially
to chlorophyllide
a
or 13
2
-hydroxychlorophyll
a
. Subsequently, chlorophyllide
a
is
degraded to pyrophaeophorbide
a
through 13
2
-hydroxychlorophyll
a
(Yamauchi et al.
1997
). Finally, 13
2
-hydroxychlorophyll
a
and pyrophaeophorbide
a
can be degraded
to colourless, low molecular weight compounds.
5.3 Degradation of Chl During Food Processing
It is well-known that blanching can inactivate chlorophyllase and enzymes, pro-
ducing a subsequent decrease in the photosynthetic capacity that is responsible for
senescence and rapid loss of green colour. The discolouration of green vegetable
