Lemon and Lime - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 375

thickness of fruits. Hence storage is used sometimes to im-
prove the quality of winter lemons, which have a tendency
to become thick skinned and dry if left long on the tree. If
fruits are allowed to overmature, their quality decline with
decreasing percent juice (25% minimum allowed), fruit
firmness, total acidity, and ascorbic acid content, while in-
creasing fruit diameter, weight, and peel thickness. Internal
browning, gumming, and drying of the pulp may also re-
sult from activities of pests like spined citrus bug and some
nutrient deficiencies (e.g., boron).

Shelf life extension
Remedies of postharvest losses can be grouped into (1)
postharvest management procedures that are critical to
maintaining quality and safety of horticultural crops; (2)
postharvest treatments designed to minimize produce con-
tamination and maximize quality; and (3) postharvest treat-
ments designed to manipulate the environment around pro-
duce in order to enhance quality (USAID, 2006).

1. Postharvest management procedures that are critical to
maintaining quality and safety of lemon and lime crops.
Packing, packaging, temperature, and humidity man-
agement are critical procedures for maintaining quality
and safety of lemon and lime fruits. Fruits for market are
cleaned and sanitized, sorted by quality and size, waxed
and treated with approved fungicide, and then packed in
shipping containers in the packinghouse. Packing pro-
tects the product against mechanical injuries and con-
tamination during marketing.
Condensation of moisture on the fruits (sweating)
over long periods of time is probably more important
in enhancing decay than is the RH of ambient air. To
avoid that, lemon and limes are stored at optimum RH
of 90-95%. Optimum RH can be achieved by one or
more of the following procedures: (1) increasing mois-
ture (water mist or spray, steam) to air by humidifiers; (2)
regulating air movement and ventilation in relation to the
produce load in the cold storage room; (3) maintaining
temperature of the refrigeration coils within about 1 ◦ C
of the air temperature; (4) providing moisture barriers
that insulate walls of storage rooms and transit vehicles;
(5) adding polyethylene liners in containers and using
perforated polymeric films for packaging; (6) wetting
flours in storage rooms; and (7) adding crushed ice in
shipping containers or in retail displays for commodities
that are not injured by the practice.
Temperature management is the most effective tool
for extending the shelf life of fresh fruits and begins
with the rapid removal of field heat using one of the
cooling methods in Table 20.8 (FAO, 1989; USAID,
2006).
Maintaining an adequate concentration of sanitizer
in water is essential to kill microbes before they attach
or become internalized in produce. This is important in
some preharvest water uses (such as spraying pesticides
or growth regulators) and in all postharvest procedures
involving water, including washing, cooling, water-
mediated transport (flumes), and postharvest drenching
with CaCl 2 or other chemicals. In addition, worker
hygiene and sanitation practices during production,

External quality
Although fruit's shape is largely governed by variety, shape
can also change as the fruit matures or as the trees get older.
An example is the 'Verna' lemon, which, when produced
from young trees, has a prominent neck that appears less
pronounced as trees mature or when fruit is left to hang late
on the tree.
Fruit size is influenced by variety, rootstock, crop load,
and irrigation practices. When there is a heavy crop or
high numbers of fruit, average fruit size decreases. Good
irrigation practice is important in achieving good fruit set
and obtaining maximum fruit size.
Peel quality and skin thickness are significantly influ-
enced by rootstock, nutrition, and environmental condi-
tions. The balance of nitrogen, phosphorus, and potassium
significantly influences peel characteristics; excessive ni-
trogen and potassium results in fruits that are puffy and
have thick peels and excessive nitrogen can also delay peel
color development. The amount of peel oil increases as the
fruit develops and matures as well as with increased ni-
trogen, while increased potassium depresses oil yield. The
best lemons have skin of an oily, fine texture and are heavy
for their size, with a lot of juice and fewer seeds and waste
fibers. High-quality lemons are firm, but not hard, to the
touch, and of a deep yellow color for ripeness and juice.
Lemons that show signs of bruises following mechanical
injury are susceptible to mold. Decay on the fruit appears as
a mold or a discolored soft area at the stem end. Shriveled
or hard-skinned fruits, or those that are soft or spongy to the
touch, are not desirable. They may be old, dried out, me-
chanically injured, or affected by a rot at the center (Anon,
2010b). The incidence of pests, diseases, and wind can sig-
nificantly reduce the external quality of fruit, hence good
pest and disease management is essential.
Lemon and lime fruits for fresh markets must be at-
tractive and wholesome in appearance; physiological dis-
orders, defined as the breakdown of fruit tissue not caused
by microbes or mechanical damage, must be prevented or
minimized (Goodrich, 2003).