Carotenoids and flavonoids are both large families of chemical
compounds. These compounds are present in the leaves along with
chlorophyll, but the high levels of chlorophyll present in the summer
months usually masks their colours. As the chlorophyll degrades and
disappears in autumn, their colours become more noticeable – both
families of compounds contribute yellows, whilst carotenoids also
contribute oranges and reds. These compounds do also degrade along with
chlorophyll as autumn progresses, but do so at a much slower rate than
chlorophyll, and so their colours become visible. Notable carotenoids
include beta-carotene, the cause of the orange colour of
carrots, lutein, which contributes to the yellow colour of egg yolks,
and lycopene, which is also responsible for the red colour of tomatoes.
