Recommendations for
Maintaining Postharvest Quality
Maturity
Indices
Garlic can
be harvested at different stages of development for specialty markets, but most
garlic is harvested when the bulbs are well mature. Harvest occurs after the
tops have fallen and are very dry. In china, the year's crop comes in May/June.
Quality
Indices
Grades are based primarily on
external appearance texture and freedom from defects.
Pure white garlic:
white-skinned.
Common / Normal white garlic: white blushed rose outer skins
High quality garlic bulbs are
clean, white (or white blushed rose outer skins), and well cured (dried neck and
outer skins). The cloves should be firm to the touch. Cloves from mature bulbs
should have a high dry weight.
Size: Diameter for fresh
market is about 4.5 cm and up.
Optimum
Temperature
-1℃ to 0℃ (30℉-32℉) The
variety of garlic affects potential storage life, and the recommended conditions
for commercial storage depend on the expected storage period. Garlic can be kept
in good condition for 1-2 months at ambient temperatures 20-30℃ (68-86℉) under
low relative humidity (<75%). However under these conditions, bulbs will
eventually become soft, spongy and shriveled due to water loss. For long-term
storage, garlic is best maintained at temperatures of -1℃ to 0℃ (30-32℉) with
low relative humidity (60-70%). Good airflow is also necessary to prevent any
moisture accumulation. Under these conditions garlic can be stored for more than
9 months.
Garlic will
eventually lose dormancy, signaled by internal development of the sprout. This
occurs most rapidly at intermediate storage temperatures of 5-18℃ (41-65℉).
Garlic odor is easily transferred to other products and should be stored
separately. High humidity in the storages will favour mould growth and rooting.
Mould growth can also be problematic if the garlic has not been well cured
before storing.
Optimum
Relative Humidity
60 to 70 %
The same
time 40 X 40'/FCL are available to finish loading inside our cold storage
warehouse to maintain low temperatures and humidity
unchanging.
To
calculate heat production multiply ml CO2/kg/hr by 440 to get Btu/ton/day or by
122 to get kcal/metric ton/day.
Rates
of Ethylene Production
Garlic produces only
very low amounts of ethylene (<0.1μ kg/hr)
Responses to
Ethylene
Not sensitive to
ethylene exposure.
Responses to
Controlled Atmospheres
Atmospheres with high
CO2 (5-15%) are beneficial in retarding sprout
development and decay during storage. Atmospheres with 15% CO2 may result in some yellow translucent discoloration
occurring on some cloves after about 6 months.
Physiological
Disorders
Freeze
injury. Due to its high solids content, garlic
freezes at temperatures below -1℃(30℉).
Waxy
breakdown is a physiological disorder that
affects garlic during latter stages of growth and is often associated with
periods of high temperature near harvest. Early symptoms are small, light yellow
areas in the clove flesh that darken to yellow or amber with time. Finally the
clove is translucent, sticky and waxy, but the outer dry skins are not usually
affected. Waxy breakdown is commonly found in stored and shipped garlic but
rarely in the field. Low oxygen levels and inadequate ventilation during
handling and storage may also contribute to development of waxy
breakdown.
Pathological
Disorders
Penicillium
rots (Pencillium corymbiferum and other
spp.) are common problems in stored garlic. Affected garlic bulbs may show
little external evidence until decay is advanced. Affected bulbs are light in
weight and the individual cloves are soft and spongy and powdery dry. In an
advanced stage of decay, the cloves break down in a green or gray powdery mass.
Low humidity in storage retards rot development. Less common storage decay problems
include Fusarium basal rot (Fusarium oxysporum cepae) which infects the stem plate and
causes shattering of the cloves, dry rot due to Botrytis
allii, and bacterial rots (Erwinia spp., Pseudomonas
spp.).
Special
Considerations
To control sprout development
and lengthen the storage period, garlic may be treated with preharvest
applications of sprout inhibitors (i.e., maleic hydrazide) or be irradiated
after harvest. Outer cloves of bulbs are easily damaged during mechanical
harvest and these damaged areas discolor and decay during storage. Therefore
high quality garlic for the fresh market is usually harvested manually to avoid
mechanical damage.
Curing garlic is the
process by which the outer leaf sheaths and neck tissues of the bulb are dried.
Warm temperatures, low relative humidity, and good airflow are conditions needed
for efficient curing. Curing is essential to obtain maximize storage life and
have minimal decay.
Garlic flavor is due to
the formation of organosulfur compounds when the main odorless precursor alliin
is converted by the enzyme alliinase to allicin and other flavor compounds. This
occurs at low rates unless the garlic cloves are crushed or damaged. Alliin
content decreases during storage of garlic bulbs, but the effect of time,
storage temperatures and atmospheres has not yet been well documented.
