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GREEN-Seeds.com
vegetables & herbs
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Green Asparagus
Recommendations for Maintaining Postharvest Quality
Trevor Suslow Department of Vegetable Crops, University of California, Davis,
CA 95616
Maturity Indices
 Asparagus spears are
harvested as they emerge through the soil from the underground crowns. Typically,
spears are cut when they reach approximately 23cm(9 in.). Stalk diameter
is not a good indicator of proper maturity and associated tenderness (See
Quality Indices).
Quality Indices Quality,
fresh asparagus will be dark green and firm with tightly closed, compact
tips. Stalks are straight, tender and glossy in appearance. U.S. grades
are No. 1 and No. 2. California grades range from small ( 0.47cm / 3/16
in. ) to Jumbo (2.1cm / 13/16 ) but diameter is not a good indicator of
tenderness quality. Washington state standards, XF (Extra Fancy), are being
adopted that specify tolerances which are somewhat more stringent than U.S.
No. 1.
Optimum Temperature
0°-2°C(32°-35.6°F) Storage life is typically 14-21 days at 2°C and can
be extended up to 31 days by 7-10 days storage at 0°C and atmospheric modification.
Extended storage (~10-12 days) in air at 0°C may cause chilling injury.
Optimum Relative Humidity
95-100%; High relative humidity is essential to prevent dessication and
loss of glossiness. Drying of the butt-end of spears is a negative quality
factor. Commonly asparagus is packed and shipped in cartons with a water-saturated
pad to maintain high humidity.
Rates of Respiration
Temp. °C °F ml CO2/kg·hr 0 32 14-40 5 41 28-68
10 50 45-152 15 59 80-168 20 68 138-250 25 77
250-300 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
< 0.1µl/kg·hr at 20°C (68°F)
Responses to Ethylene
Exposure to ethylene will accelerate the lignification (toughening) of asparagus
spears in controlled studies. The concentration and duration of exposure
to exogenous ethylene, to cause this effect, at commonly encountered levels
during storage and distribution are not available. ----
Responses to Controlled
Atmospheres(CA)
Elevated CO2 at 5-10%(typically
7%) in air is beneficial in preventing decay and reducing the rate of toughening
of the spears. The beneficial effect is most pronounced if temperatures
cannot be maintained below 5°C(41°F). Short (CA) exposure to higher CO2concentrations
(12-20%) is safe and beneficial only if temperatures can be maintained at
0° - 1°C (32° - 33.8°F). Signs of CO2injury are small to elongated pits,
generally first observed just below the tips. Severe injury results in ribbiness.
Physiological Disorders
* Asparagus will continue to develop after harvest which is why low temperature
postharvest management is critical. Common disorders include upward bending
of tips away from gravity and "feathering" (expansion and opening) of tips.
Bending will also occur if tips expand to the top of the packaging and are
deflected. * Spear toughening occurs rapidly at temperatures above 10°C
( 50°F). * Bruising and tip-breakage are signs of rough handling and can
result in toughening of the spears from wound ethylene. * Asparagus is sensitive
to chilling injury after 10 days at 0°C (32°F). Symptoms of chilling injury
include loss of sheen or glossiness and graying of the tips. A limp, wilted
appearance may be observed. Severe chilling injury may result in darkening
near tips in spots or streaks * Freezing injury (water-soaked appearance
leading to extreme softening) will likely result at temperatures of -0.6°C
(30.9°F) or lower. -----
Pathological Disorders
- The most prominent postharvest disease concern is bacterial soft rot,
induced by Erwinia carotovora subsp.carotovora. Decay may initiate at the
tips or the butt end. Spears that are re-cut above the white portion of
the butt end are reported to be most susceptible to bacterial decay.
- Special Considerations Rapid hydrocooling soon after harvest is strongly
recommended. Pyramid-shaped wooden or waxed corrugated boxes for hydrocooling
combined with center-loading during shipment promote good cooling-air circulation.
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Green - Seeds Co., Ltd.
81/10B Ho Van Hue Street, Phu Nhuan District, Ward 9, Ho Chi Minh City, Vietnam
Tel: +84 (8) 847 6901 - Fax: +84 (8) 844 1392 - Email: info@green-seeds.com
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