Details on fruit ripening

1. Physiology of fruit ripening
•changes during ripening include
softening due to the enzymatic
breakdown of the cell walls,
•starch hydrolysis,
•sugar accumulation, and
•the disappearance of organic acids
and phenolic compounds, including
tannins.

2. Respiratory climateric

3. • Ethylene has strong effect on permeability
of cell membrane and cell permeability
increases during ripening
• This softens the fruit and allow the
intermingling of metabolite and enzymes
kept compartmentalized, so that
respiratory metabolism is greatly speeded
up

4. • All fruits that ripen in response to ethylene exhibit a
characteristic respiratory rise before the ripening phase
called a climacteric.
• Such fruits also show a spike of ethylene production
immediately before the respiratory rise
• treatment with ethylene induces the fruit to produce
additional ethylene, its action can be autocatalytic.
• Apples, bananas, avocados, and tomatoes are
examples of climacteric fruits.
• In contrast, fruits such as citrus fruits and grapes do not
exhibit the respiration and ethylene production rise and
are nonclimacteric fruits.

5. • Inhibitors of ethylene biosynthesis (such as
AVG) or of ethylene action (such as CO2 , MCP
or Ag) have been shown to delay or even
prevent ripening
• Cold storage and flushing the fruits with an inert
gas (N2 or CO2) retards ripening
• never-ripe mutation in tomato: this mutation
completely blocks the ripening of tomato fruit.
never-ripe was due to a mutation in an ethylene
receptor that rendered it unable to bind ethylene

6. gene expression during ripening is regulated by at
least two independent pathways:

7. biochemical changes associated
with ripening
• 1) Conversion of acids & starch to free sugars
• 2) elaboration of pectinases which soften and ultimately
breaks down cell walls
• 3) ellaboration of the pigment anthocyanin and
carotenoids
• In apples conc. of starch increases and then decreases
until harvest, as it is converted to sugars
• In apples & pears fructose is abudant sugar, but lesser
amount of glucose, sucrose & sugar alcohol also are
present
• Cherries & grapes contain equal amount of glucose and
fructose
• In oranges and grapes, with ripening the organic acid
content decreases thus giving sweet taste
• In lemon, acid continue to increase during ripening, so
that pH decreases and fruit remains sour