2009_Book_FoodChemistry

848 18 Fruits and Fruit Products
butane-1,4-diamine] belong to the group of
naturally occurring anti-senescence agents. They
increase during the early phase of growth of the
fruit, when intensive cell division takes place,
and, apart from exceptions, decrease during
ripening. Studies have shown that the treatment
of fruit with polyamines results in a slowing
down of the ethylene production and respiration,
which in turn has a positive effect on the firmness
of the fruit flesh and on the color.
18.1.4.2.2 1-Methylcyclopropene (MCP)
As a result of structural similarities, MCP docks
on to receptor proteins for ethylene, causing it to
lose activity. The texture and color of apples and
pears (sensitive varieties) do not change through
months of cool storage. The sugar content also
remains constant while the acid content increases.
Gaseous MCP adsorbed on dextran is used for the
treatment of fruit. The MCP is liberated by the
addition of water. The concentrations applied are
in the range 300–1000 ppb.
18.1.5 Storage of Fruits
18.1.5.1 Cold Storage
Fig. 18.10. The effect of ethylene on fruit respiration.
(a) climacteric, (b) nonclimacteric. Numerals on the
curves: ethylene in air, ppm (according to Biale, 1994)
18.1.4.2 Anti-Senescence Agents
In order to keep fruit fresh, the ripening is slowed
down by cold storage (cf. 18.1.5) and/or with additives
which inhibit the formation or action of
ethylene.
The suitability, duration and required conditions
of fruit storage are dependent on variety and
quality. Commonly used conditions are −1 ◦ Cto
+2 ◦ C at 80–90% relative humidity. The storage
time varies from 4–8 months for apples, 2–6
months for pears, 2–3 months for grapes, 1–2
weeks for strawberries and raspberries, and 4–5
days for cherries. Efficient aeration is required
during storage. Air circulation is often combined
with purging to remove ethylene, the volatile
promoter of fruit ripening. Weight losses occur
during fruit storage due to moisture losses of
3–10%.
18.1.4.2.1 Polyamines
The polyamines putrescine (butane-1,4-diamine),
spermidine [N-(3-aminopropyl)butane-1,4-diamine]
and spermine [N,N ′ -bis-(3-aminopropyl)-
18.1.5.2 Storage in a Controlled (Modified)
Atmosphere
This term is applied to an atmosphere which, in
comparison to air, has a lowered oxygen con-