This document summarizes the biochemistry of fruit ripening. It discusses how ethylene acts as a ripening hormone, triggering climacteric ripening through a process of biosynthesis. Ethylene production is regulated by the enzymes ACC synthase and ACC oxidase. During ripening, ethylene causes chlorophyll degradation and synthesis of pigments like carotenoids and anthocyanins. It also increases the production of volatile compounds and enzymes involved in softening through cell wall degradation. Overall, the document provides an overview of the key biochemical processes and changes involved in fruit ripening mediated by the plant hormone ethylene.

1. Biochemistry of fruit
Ripening
Presented by: Meet Padhiyar
Reg. No: 04-BSMS-02353-2020
MSc. 2nd Semester , biochemistry
Presented to: Dr. V H Kanabi
Associate professor at College of
Basic Science and Humanities,SDAU

2.  Index
1. Introduction
2. Ethylene
3. Mechanism of ripening
4. Biosynthesis of ethylene
5. Role of ethylene in fruit ripening
6. Changes during ripening
7. Reference

3.  Introduction of Ethylene :
 Ethylene (C2H4) is a simple, natural, gaseous plant
hormone.
 It is produced by higher plants, bacteria, and fungi and
influences many aspects of plant growth and development.
 It is also called as Ripening Hormone as it plays an important
role on ripening process.
 Low concentration of 0.1 – 1.0 microliters is sufficient to
trigger the ripening process in climacteric fruits.

4.  The ripening of fruit is to be regarded as a special form of
senescence.
 The effect of gaseous ethylene can be demonstrated by
placing a ripe apple and a green tomato together in a plastic
bag;
 Ethylene produced by the apple accelerates the ripening of
the tomato.

5.  Ethylene can easily be synthesized in all plant organs such
as roots, stems, leaves, tubers, fruits and seeds.
 Within the plant organs, ethylene formation is mainly located
in peripheral tissues.
 Ethylene can easily pass through plasmamembrane into the
cell, easily diffuse within the plant, and flushed out of plant
tissues through intercellular spaces (Being a gas, ethylene
moves by diffusion from its site of synthesis).

6. Mechanism of ripening

7.  Biosynthesis of ethylene
 S-adenosylmethionine is the precursor for the synthesis of ethylene
 The positive charge of the sulfur atom in S-adenosyl methionine
enables its cleavage to form a cyclopropane,
 In a reaction catalyzed by aminocyclopropane carboxylate synthase,
abbreviated ACC synthase
 Subsequently, ACC oxidase catalyzes the oxidation of the
cyclopropane to ethylene, CO2, HCN, and water
 HCN is immediately detoxified by conversion to b-cyanoalanine.

8.  Process

9.  Genetic engineering has been employed to suppress
ethylene synthesis in tomato fruits in two different ways :
1. The activity of ACC synthase and ACC oxidase was
decreased by antisense technique
2. By introducing a bacterial gene into the plants, an enzyme
was expressed that degraded the ACC formed in the tomato
fruits so rapidly that it could no longer be converted to
ethylene by the ACC oxidase
 The aim of this genetic engineering is to produce tomatoes that
keep better during transport.

10.  Role of ethylene in fruit ripening
 Ripening is a process in fruits that makes it acceptable for
consumption. The fruit becomes sweeter, and softer.
 During ripening starch is converted to sugar.
 The fruit is said to be ripe when it attains its full flavour and
aroma (watada et al.. 1984).
 Ripening causes colour change in the fruit.
 Based on ripening behaviour, fruits are classified as,
1.Climacteric
2.Non Climacteric

11.  External ethylene Hasten climacteric rise (climacteric
fruit)accompanied by an increase in oxygen uptake. This
process is notreversed.
 External ethylene Increase Respiration (Non-climacteric fruit)
 During ripening both carbon dioxide and ethylene increase
significantly.

12. Changes during ripening
 Increase in rate of respiration
 Chlorophyll degradation
 Synthesis of carotenoids & anthocyanins
 Production of volatile compounds
 Increase in activity of enzymes
 Texture softening and degradation of cellwall
 Change in Organic Acids

13. Increase in rate of respiration
 Stored organic materials → Simple end product + Energy
(carbohydrates,protein,fats)
 The major storage products sucrose and starch are fully
oxidized to CO2 and H2O
 Energy release in the form of ATP.
 There are two pathways in conversion of starch or sucrose to
glucose-6 P
1. glycolysis
2. pentose phosphate pathway

14. Chlorophyll degradation
1. Degradation of chlorophyll
in presence of
Chlorophyllase enzyme
2. Breakdown of chlorophyll
into phytol chain &
porphyrin
3. Loss of Mg++ ion and
conversion of porphyrin into
Phaeophytin
4. Change in tetrapyrolic chain
and it becomes bilivirdin
5. Oxidation of doublebonds
• Step

15. Synthesis of carotenoids &
anthocyanins
 Carotenoids are lipophilic secondary metabolites derived from the
isoprenoid pathway and are accumulated in most plant organs
 They contribute to the red, yellow and orange colors of many fruits and
flowers, and are a factor in attracting pollinators to flowers.
 In plants, they are synthesized in plastids of photosynthetic and sink
organs and are essential molecules for photosynthesis, photo-oxidative
damage protection and phytohormone synthesis.

16. Anthocyanins :
 Anthocyanins are responsible for pink, red,
purple, and blue colors.
 Water-soluble pigments formed during
maturation of fruits (strawberries, apples,
cranberries, grapes) and vegetables (red
cabbage, radish, red onion...)
 Anthocyanins are flavonoid pigments whose
structure is based on the phenyl propanoid
nucleus

17. Production of volatile compounds
 Esters of aliphatic alcohols and short chain fatty acids.
 In fruits, major volatile compounds are isoamyl acetate,
aldehydes and terpenoid compounds.
 Volatiles originate from proteins, carbohydrates, lipids, and
vitamins.
 Taste is provided by many non-volatile components, including
sugars and acids present in fruits.
 Short-chain unsaturated aldehydes and alcohols (C3-C6) and
esters are important contributors to the aroma.

18. Activity of enzymes
1. Pigmentation : Degradation of chlorophyll and synthesis of new
pigment by Chlorophyllase.
2. Glycolytic Action : by Glucose phosphate isomerase
3. Hydrolytic Action : conversion of starch to sugar by amylase,
beta amylase.
4. Oxidation: catalase and peroxidase
5. Softening: it is due to degradation of pectin by pectinase.
6. Degradation of cellulose for ripening by celllase.

19. Texture softening and degradation
of cellwall
 Textural softening is the result of enzymatic degradation of
structural as well as storage polysaccharides.
1. Breakdown of starch
2. Breakdown of substance
3. Reduced cellular rigidity
4. Softening

20. Time

21. Cell wall Degradation
 Plant cell wall composed of complex polysaccharides, proteins, cellulose.hemicellulose
and pectin substances.
 Due to activation of certain enzymes soluble pectins increasing which results
indecrease in firmness and cell wall degradation.
 Cell wall degradation involved :
1. Depolymerisation
2. De-esterification
 Enzymes responsible for cell wall degradation
1. Hydrolases
2. Pectineasterase
3. Polygalacturonase
4. Cellulase
5. Beta-galactosidase

22. Change in Organic Acids
 The total organic acids(malic+ citric+quinic) is decreased with
ripening of fruits (Wang et al 1993).
 The decline in the content of organic acids during ripening is
the result of an increase in membrane permeability.
Onset
Of
Ripening
Increase
membrane
permeability
Reduction in
translocation from
the leaves
Conversion
of starch to
sugar
Leading to
dilution of acids
Increase in
volume of fruit
Acids are used
in respiration

23. Reference
 HW, Heldt. “Ethylene makes fruit ripen." Plant
Biochemistry.(Eds.: Hans-Walter Heldt in cooperation with
Fiona Heldt) Elsevier. San Diego, USA. p (2005):474-476.

24. THANK
YOU