Agriculture Reference
In-Depth Information
12 -14 C and 90-95%, depending on cultivar, maturity
stage at harvest, and intended distribution and transport
time (Goodrich, 2003; Kimball et al., 2005). An interest-
ing and specific example of long-term lemon storage is the
traditional practice of harvesting lemons in middle to late
winter, and storing them until the summer marketing sea-
son. These lemons, when picked, are green, thick skinned,
and not very juicy, but after storage (termed curing), they
are yellow, juicy, and thin skinned.
Adverse preharvest or postharvest conditions or nutri-
tional deficiencies during growth and development can
cause physiological disorders in lemons. Fresh citrus fruits
are more prone than pome fruits (apples, pears) to a par-
ticular type of physiological disorder, termed chilling dis-
order. In lemons, storage at suboptimal temperatures can
lead to symptoms such as pitting of the flavedo, membrane
browning, and red blotches. Lemons should not be stored at
temperatures below 10 C (Goodrich, 2003; Kimball et al.,
2005).
Limes are more stable than many other citrus fruits due
to their extreme high acidity and low pH. Problems may,
however, be encountered at certain temperatures and hu-
midity with growth of acid tolerant surface fungi. Biolog-
ical growth regulators have been effective in controlling
the growth of acid tolerant surface fungi. For example, in
'Persian' limes, 2,4-dichlorophenolindophenol (2,4-D) and
gibberellic acid (GA) have been successful in reducing the
growth of Penicillium -type molds, yellowing, mottling, and
discoloration of the rinds during storage. In addition, the
use of optimum storage conditions for fresh fruit (10 Cand
90-95% relative humidity) gives a storage life of up to 4
weeks (Berry, 2003). GA has the ability to reduce aging of
fruit rind and rind color development in stored lemon and
lime when applied as a tree spray at 10 ml (of 100 g/liter
product)/100 liter water about 4-6 weeks before harvest
when fruit are silver-green (Baldwin, 1993). The 2,4-D is
also effective in preventing button death and subsequent
stem end rot development in lemon.
Another factor that can cause problems in long-term stor-
age is ethylene gas, which is produced from stressed or
decaying fruit and can accumulate in an enclosed environ-
ment and accelerate the coloring and aging process in the
fruit (Baldwin, 1993; Hardy, 2004). Removal of ethylene
can be achieved on small-scale using bags of ethylene ab-
sorbers made from porous material carrying potassium per-
manganate left in the storage rooms or suspended from the
ceilings. Large-scale removal of ethylene can be achieved
using ultraviolet tubes, which release ozone and atomic
oxygen that breaks down the ethylene. Where fruits are
stored on a routing basis, the ethylene problem is overcome
by continuous venting of storage rooms, meaning that the
new air has to be refrigerated to the storage temperature, and
this can be expensive, particularly during summer months
(Baldwin, 1993).
MARKET QUALITY AND SHELF LIFE
EXTENSION
Market quality of lemon and lime fruit
All citruses are nonclimacteric fruit because they ripen
gradually over weeks or months and are slow to abscise
from the tree. External color changes during ripening is a
function of climate rather than ripeness, hence it is a poor
indicator of maturity. The best indices of maturity for citrus
are internal: sugar ( Brix), acid content, and the sugar/acid
ratio (Rieger, 2006).
Grade and quality are two important terms in under-
standing citrus fruit quality, markets, and economics. Grade
refers to external characteristics such as size, presence of
blemishes, and appearance, while maturity refers to inter-
nal characteristics such as juice content, taste, total solu-
ble solids (TSS), acid content, titratable acidity (TA), and
the ratio of TSS to TA. As with most produce for the
fresh market, appearance is the primary attribute of qual-
ity for fresh market lemons and limes. Grading is critical
and standardized in a given country or region. Quality in-
dices include color intensity and uniformity; size (larger
lemons are preferred), visually pleasing shape and smooth-
ness; and freedom from exterior blemishes, splotches, and
rind discoloration. Fresh fruit pricing in most lemon and
lime-producing countries is based on these factors, along
with market supply and demand (Hardy, 2004).
Internal quality
Lemons are naturally acidic, being high in total acidity and
low in TSS compared to other citrus varieties (excepting
acid limes). The organic acid content increases with
fruit development whereas in oranges it decreases. The
accumulation of acid is highly correlated with temperature;
fruits tend to have higher quantities of acid per limit weight
of fruit in hot tropical and subtropical regions. Rootstock
influences fruit acidity depending on variety; fruits grown
on “Rough” lemon rootstock have lower acidity than
those grown on Poncirus trifoliata. Generally, increasing
salinity results in a decrease in percent juice, acidity,
and TSS, and the degree of impact is also influenced by
rootstock.
Medium- and long-term postharvest storage of fruits can
increase the juice contents and acidity and reduce peel
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