Food Chemistry

848 18 Fruits and Fruit Products

Fig. 18.10.The effect of ethylene on fruit respiration.
(a) climacteric, (b) nonclimacteric. Numerals on the
curves: ethylene in air, ppm (according toBiale, 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 add-
itives which inhibit the formation or action of
ethylene.

18.1.4.2.1 Polyamines

The polyamines putrescine (butane-1,4-diamine),
spermidine [N-(3-aminopropyl)butane-1,4-di-
amine] and spermine [N,N′-bis-(3-aminopropyl)-

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

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%.

18.1.5.2 Storage in a Controlled (Modified)

Atmosphere

This term is applied to an atmosphere which, in

comparison to air, has a lowered oxygen con-