Agriculture Reference
In-Depth Information
• The time of day when harvesting operations are
conducted and the time interval between irrigation, or
rainfall and harvest, can also influence decay and peel
injuries.
• The duration of time that fruit remains in the orchard
after harvest prior to removal can also affect fruit quality
at the end of the supply chain.
• The mode of transferring the harvested product from the
picking bag to the crates or bins may also cause wound-
ing and affect the quality of the final product, if not done
with care.
• General hygiene maintenance practices of continual
practical cleaning of picking bags, crates or bins or the
trailer used in transport of fruit from the orchard to the
pack house, are essential to reduce potential build-up of
inoculum due to the retention of infected fruit debris
contaminating the next batch harvested.
mainly used to improve the visual quality of, otherwise,
mature fruit. Citrus fruit showing some natural colour is
harvested and in most cases first treated with a fungicide
prior to placing it in de-greening rooms or under plastic
tents. The 'trickle' method is the most common way to
apply ethylene, which involves continually replacing the
air in the de-greening area with a low concentration of
ethylene. The commercial successful application of de-
greening has been reported (Cohen 1978). The concentra-
tion of ethylene is usually around 5 ppm, and should not
exceed 10 ppm. Early citrus varieties can also be de-
greened by using ethephon (2-chloroethyl phosphoric acid;
2-CEPA; Murata 1997). De-greening can be achieved at
15-25°C depending on the volumes of fruit treated, the
facility design and concentration of ethylene used. Efficient
airflow and ventilation allows even distribution of the
ethylene and removes accumulated carbon dioxide. The
common air ventilation recommendation of one room
volume per hour is empirical, but its success is related to
good room design and automated humidity control
(Wardowski
et al
. 2006). The most undesirable effect of
de-greening under low humidity is fruit softening, and
exacerbation of injuries and rind weaknesses.
Packing facilities and processes
Pack houses generally consist of a receiving area, packing
line with sizing and grading areas and storage/dispatch
areas. Common pack house practices and the order that
they occur in are given below.
Bin drenching
It is common practice in some countries to use bin drench-
ing at the pack house prior to fruit off-loading. The concept
is to apply the first fungicide application to fruit as soon as
possible after harvest, and preferably as a bulk dip or high-
volume drench on arrival at the packing facility. Dipping or
drenching bins of citrus with fungicides are undertaken
because most injuries and subsequent inoculation of fruit,
occur during harvest. A recommended practice is to apply
fungicide treatments within 24 hours after harvest to pre-
vent or reduce mould development (Tugwell 1999).
However, this recommendation is often considered imprac-
tical or costly and not adequate for all fungicide groups
(Wild & Spohr 1989). Alternative practices include the use
of disinfectants in washing water and soaps to remove field
dust from fruit at the point of receival. Washing water is
often also recirculated and should therefore be sanitised or
filtered to remove inoculum in the receival tank at the pack
house.
Ethylene effects on citrus colouring
Ethylene is a natural growth regulator produced by most
fruits as a response to stress or during the natural ripening
process. Ethylene does not ripen citrus fruits; as such, the
acid, sugars and flavour of the juice are unaffected.
Goldschmidt
et al
. (1993) observed the response of citrus
fruit to ethylene which resulted in colour change due to an
increase in chlorophyll degradation and the promotion of
carotenoid biosynthesis. Ethylene thus destroys chloro-
phyll, and promotes the development of yellow and orange
carotenoids in the flavedo (Stewart and Wheaton 1972).
Under conditions of mild stress, such as cold nights, citrus
de-green naturally. The post-harvest use of ethylene seeks
to chemically hasten the de-greening process.
Ethylene effects on decay
Ethylene promotes senescence (aging), which increases
the susceptibility of citrus to decay. The temperature (typi-
cally 22°C to 24°C) and high humidity (ideally 95% RH)
required for ethylene de-greening also provides ideal con-
ditions for the development of post-harvest disease.
Ethylene accelerates senescence of the fruit calyx, which
favours 'stem-end rots' (e.g.
D. natalensis
,
P. citri
and
A. citri
). Ethylene also plays a role in the induction of
anthracnose decay (
C. gloeosporiodes
). The level of ethyl-
ene used in de-greening is considered important. Ethylene
De-greening
Many citrus cultivars can be palatable while their peel
colour is still green. However, consumer perception is that
green citrus are associated with immaturity and the use of
ethylene to 'de-green' the fruit is therefore a common
commercial practice in many countries. This method is
