GREEN SEED COAT COLOUR RETENTION IN LENTIL - University ...

2.7 Bleaching of green colour in field pea
Bleaching or weathering that compromises the appearance of green in field pea
is very important economically. One major parallel between bleaching in pea
cotyledons and green seed coat colour loss in lentil is that both involve a decrease in
the desirability of perceived green colour. Similar to green lentil, the value of green
field pea is affected by the perceived colour of the seed. In the case of green pea,
the cotyledons are green and the seed coat is opaque. Green peas are consumed
whole or decorticated and split, instead of eaten whole like green lentil. The more
green the sample appears the more it is worth in the market place. Bleached seeds
may also exhibit reduced germination and emergence when used for planting
(Riehle and Muehlbauer, 1975).
There are several compounds that affect bleaching in field pea but
chlorophyll is the most important (Cheng et al., 2004). It has been shown that
bleached green peas have a higher content of lutein in the cotyledons compared to
the unbleached samples. A low chlorophyll a:b ratio in the seed coat of green peas
can cause the seed coat to appear less green (McCallum et al., 1997, Cheng et al.,
2004, and Chao et al., 1995). The low ratio is expected because chlorophyll a is less
stable than chlorophyll b. Another possible reason is that chlorophyllase has a
higher affinity for chlorophyll a than chlorophyll b. This is often observed in
senescing leaves (Raven et al., 1999).
When green pea seeds are soaked in water and subsequently exposed to
light, the chlorophyllase activity increases significantly compared to unsoaked seeds
as the seed leaves the dormant state. This explains why subsequent dehydration of
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