[PDF]Postharvest Handling for Organic Crops

VEGETABLE
RESEARCH AND
INFORMATION
CENTER

Small Farm Organic
Program Veg y etab|e

Production in
California

Series vric.ucdavis.edu




POSTHARVEST HANDLING
FOR ORGANIC CROPS

TREVOR SUSLOW,

UC Cooperative Extension
Vegetable Crops Specialist,
UC Davis



www.sfc.ucdavis.edu



Specific information on organic vegetable production practices in California is scarce, and growers need sound information
to guide their management decisions. The Organic Vegetable Production in California Series is made up of publications
written by Farm Advisors and Specialists from the University of California's Division of Agriculture and Natural
Resources. Each publication addresses a key aspect of organic production practices applicable to all vegetable crops.



Optimal-quality organic produce that achieves the
desired textural properties, sensory shelf life, and nutri-
tional content is the combined result of careful imple-
mentation of recommended production inputs and
practices, careful handling at harvest, and appropriate
postharvest handling and storage. This publication is
an overview of general postharvest handling considera-
tions unique to the marketing of registered or certified
organic produce, with a brief introduction to currently
permitted and restricted postharvest treatments.

PLANNING FOR POSTHARVEST QUALITY

The effort to achieve an economic reward through the
marketing of organic produce must begin well before
harvest. Seed selection can be a critical factor in deter-
mining the postharvest performance of any commodi-
ty. Individual cultivars vary in their inherent potential
for firmness retention, uniformity, disease and pest
resistance, and sensory shelf life, to list a few key
traits. Cultivars chosen for novelty or heirloom traits
may be suitable for small-scale production and local
marketing but would be disastrous choices if the mar-
keting plan included shipment to more distant mar-
kets. In addition to genetic traits, environmental fac-
tors such as soil type, temperature, wind during fruit
set, frost, and rainy weather at harvest can have
adverse effects on storage life, suitability for shipping,
and quality. Cultural practices may have dramatic
impacts on postharvest quality. For example, poor
seedbed preparation for carrots may result in sun-
burned shoulders and green cores in many of the spe-
cialty carrots favored by consumers at farmer's mar-
kets. Other titles in the Organic Vegetable Production
in California Series give more detail on suitable pro-
duction practices.



Planning for postharvest food safety should be
included in any crop management plan. Good
Agricultural Practices (GAP) need to be developed and
formalized for each crop and specific production field
to minimize the risk of a variety of hazards or contami-
nants: chemical (e.g., heavy metals carryover), physical
(e.g., sand and soil, wood, plastic or metal shards), and
biological (e.g., Salmonella, Listeria, mycotoxins). Prior
land use, adjacent land use, water source and method
of application, fertilizer choice (such as the use of
manure), compost management, equipment mainte-
nance, field sanitation, movement of workers between
different operations, personal hygiene, domestic animal
and wildlife activities, and other factors have the poten-
tial to adversely impact food safety.

It is worth noting that many elements of a GAP plan
are likely to be incorporated into the existing organic
crop management program and activities. Programs in
place to ensure produce quality may be directly applic-
able to food safety with minor modifications. The appli-
cation of food safety programs, in turn, has been shown
to directly benefit postharvest quality.

Once prerequisite production programs are in place,
a systematic evaluation and implementation plan of
Good Agricultural Practices during harvest operations
and any subsequent postharvest handling, minimal or
fresh-cut processing, and distribution to consumers
must be developed. Considerations for these activities
are covered below.

HARVEST HANDLING

The inherent quality of produce cannot be improved
after harvest, only maintained for the expected window
of time (shelf life) characteristic of the commodity. Part
of what makes for successful postharvest handling is an



University of California • Division of Agriculture and Natural Resources

Publication 7254

http://anrcataloq.ucdavis.edu



Postharvest Handling for Organic Crops • 2



accurate knowledge of what this window of opportuni-
ty is under your specific conditions of production, sea-
son, method of handling, and distance to market.
Under organic production, growers harvest and market
their produce at or near peak ripeness more commonly
than in many conventional systems. However, organic
production often includes more specialty varieties
whose shelf lives and shipping traits are reduced or
even inherently poor. As a general approach, the fol-
lowing practices can help you maintain quality:

1. Harvest during the coolest time of day to maintain
low product respiration.

2. Avoid unnecessary wounding, bruising, crushing, or
damage from humans, equipment, or harvest con-
tainers.

3. Shade the harvested product in the field to keep it
cool. By covering harvest bins or totes with a reflec-
tive pad, you greatly reduce heat gain from the sun,
water loss, and premature senescence.

4. If possible, move the harvested product into a cold
storage facility or postharvest cooling treatment as
soon as possible. For some commodities, such as
berries, tender greens, and leafy herbs, one hour in
the sun is too long.

5. Do not compromise high quality product by min-
gling it with damaged, decayed, or decay-prone
product in a bulk or packed unit.

6. Only use cleaned and, as necessary, sanitized pack-
ing or transport containers.

These operating principles are important in all oper-
ations but carry special importance for many organic
producers who have less access to postharvest cooling
facilities.

POSTHARVEST STORAGE

Temperature is the single most important tool for main-
taining postharvest quality. For products that are not
field-cured or exceptionally durable, the removal of
field heat as rapidly as possible is highly desirable.
Harvesting cuts a vegetable off from its source of water,
but it is still alive and will lose water, and therefore tur-
gor, through respiration. Field heat can accelerate the
rate of respiration and with it the rate of quality loss.
Proper cooling protects quality and extends both the
sensory (taste) and nutritional shelf life of produce. The
capacity to cool and store produce gives the grower
greater market flexibility. Growers have a tendency to
underestimate the refrigeration capacity needed for
peak cooling demand. It is often critical that fresh pro-
duce rapidly reach the optimal pulp temperature for
short-term storage or shipping if it is to maintain its



highest visual quality, flavor, texture, and nutritional
content. The five most common cooling methods are
described below.

Room cooling - an insulated room or mobile container
equipped with refrigeration units. Room cooling is
slower than other methods. Depending on the com-
modity, packing unit, and stacking arrangement, the
product may cool too slowly to prevent water loss,
premature ripening, or decay.

Forced-air cooling - fans used in conjunction with a cool-
ing room to pull cool air through packages of pro-
duce. Although the cooling rate depends on the air
temperature and the rate of airflow, this method is
usually 75 to 90% faster than simple room cooling.
Design considerations for a variety of small- and
large-scale units are available in Commercial Cooling
of Fruit, Vegetables, and Flowers (ANR Publication
21567).

Hydrocooling - showering produce with chilled water
to remove heat, and possibly to clean produce at
the same time. The use of a disinfectant in the water
is essential, and some of the currently permitted
products are discussed later in this publication.
Hydrocooling is not appropriate for all produce.
Waterproof containers or water-resistant waxed-
corrugated cartons are required. Currently waxed
corrugated cartons have limited recycling or sec-
ondary use outlets, and reusable, collapsible plastic
containers are gaining popularity. A list of vegeta-
bles that are suitable for hydrocooling is available
in Postharvest Technology of Horticultural Crops (ANR
Publication 3311) as well as in Commercial Cooling of
Fruit, Vegetables, and Flowers.

Top or liquid icing - an effective method to cool tolerant
commodities, and equally adaptable to small- or
large-scale operations. Ice-tolerant vegetables are
listed in Postharvest Technology of Horticultural
Crops and in Commercial Cooling of Fruit,
Vegetables, and Flowers. It is essential that you
ensure that the ice is free of chemical, physical, and
biological hazards.

Vacuum cooling - uses a vacuum chamber to cause the
water within the plant to evaporate, removing heat
from the tissues. This system works well for leafy
crops that have a high surface-to-volume ratio,
such as lettuce, spinach, and celery. The operator
may spray water onto the produce before placing
it into the vacuum chamber. As with hydrocooling,
proper water disinfection is essential (see Sanita-
tion and Water Disinfection). The high cost of the
vacuum chamber system restricts its use to larger
operations.



Postharvest Handling for Organic Crops • 3



The considerations for and selection of appropriate
cooling methods and appropriate storage temperature
and humidity conditions for a large diversity of vegeta-
bles are discussed in the two ANR publications men-
tioned above. In large cooling operations that handle
both conventional and organic commodities, it is com-
mon to hydrocool (or water-spray vacuum-cool) organ-
ic produce at the beginning of daily operation, after a
full cleaning of the facility and a complete water
exchange. This practice is intended to prevent carryover
or cross-contamination of organic produce with syn-
thetic pesticide or other prohibited residues. This will
generally require at least overnight short-term storage
of the produce. The injection of ozone into the cooling
water stream has been shown to reduce substantially
the pesticide residues that may remain in the water
after it is used to cool non-organic produce.

Other postharvest issues that involve combined
steps of unloading commodities from harvest bins,
washing, and precooling must also be evaluated for
adherence to organic standards. Some operators use
flotation as a way to reduce damage at the point of
grading and packing. Entire bins are submerged in a
tank of water treated with a chemical flotation aid that
allows the picked product to be gently removed and
separated from the container. Lignin sulfonates are
allowed in certified organic handling as flotation aids
for water-based unloading of field bins or other density
separation applications.

SANITATION AND WATER DISINFECTION

Preventive food safety programs, sanitation of equip-
ment and food contact surfaces, and water disinfection
should be integrated into every facet of postharvest
handling. Food safety and decay/spoilage control are
concerns for produce handlers at all scales of produc-
tion. Escherichia coli (E. coli) 0157:H7, Salmonella,
Shigella, Listeria, Cryptosporidium, Hepatitis, and
Cyclospora are among the diseases and disease-causing
organisms that have been associated with fresh fruits
and vegetables. Several cases of foodborne illness have
been traced to poor or unsanitary postharvest practices,
especially to nonpotable cooling water and ice.

For organic handlers, the nature and prior use of
cooling water is a special consideration. Postharvest
water cannot at any time contain prohibited substances
in dissolved form. Responsibility for this applies to the
organic producer, handler, processor, and retailer. Even
incidental contamination from a prohibited material
would keep the product from being certified organic.
Organic producers, packers, and handlers are required
to keep accurate, specific records of postharvest wash or
rinse treatments, identified by brand name and source.



For a more complete discussion of water disinfection,
see Postharvest Chlorination (ANR Publication 8003).

Briefly, the proper use of a disinfectant in posthar-
vest wash and cooling water can help prevent both
postharvest diseases and foodborne illnesses. Because
most municipal water supplies are chlorinated and the
vital role of water disinfection is well recognized,
organic growers, shippers, and processors may use
chlorine within specified limits. All forms of chlorine
(e.g., liquid sodium hypochlorite, granular calcium
hypochlorite, and chlorine dioxide) are restricted mate-
rials as defined by existing organic standards. The
application must conform with Maximum Residual
Disinfectant Limit under the Safe Drinking Water Act,
currently 4 mg/L (4 ppm) expressed as Cl 2 . The
California Certified Organic Farmers (CCOF) regula-
tions have permitted this threshold of 4 ppm residual
chlorine, measured downstream of the product wash
(due to food safety concerns, CCOF has recently modi-
fied this threshold to permit 10 ppm residual chlorine
measured downstream of the wash step). Growers cer-
tified by other agencies should check with their certify-
ing agent.

As a general practice, field soil on product, bins,
totes, and pallets should be kept to a minimum by pre-
washing the produce before loading it. This will signifi-
cantly reduce the demand for disinfectant in the water
and lower the total required volume of antimicrobial
agents. Prewashing also removes plant exudates
released from harvest cuts or wounds, which can react
rapidly with oxidizers such as hypochlorite and ozone,
and so requires higher rates of the chemical to maintain
the target 4 to 10 ppm downstream activity.

For both organic and conventional operations, liquid
sodium hypochlorite is the most common form used.
For optimum antimicrobial activity with a minimal con-
centration of applied hypochlorite, the pH of the water
must be adjusted to between 6.5 and 7.5. At this pH
range, most of the chlorine is in the form of hypochlor-
ous acid (HOC1), which delivers the highest rate of
microbial kill and minimizes the release of irritating
and potentially hazardous chlorine gas (Cl 2 ). Chlorine
gas will exceed safe levels if the water is too acidic.
Products used for pH adjustment also must be from a
natural source such as citric acid, sodium bicarbonate,
or vinegar. Calcium hypochlorite, properly dissolved,
may provide benefits of reduced sodium injury to sen-
sitive crops (e.g., some apples varieties), and limited
evidence points toward extended shelf life for tomatoes
and bell peppers due to calcium uptake. Amounts of
sodium hypochlorite to add to clear, clean water for
disinfection are given in the table on the next page.

Ozone is an attractive option for water disinfection
and other postharvest applications. Ozonation is a



Postharvest Handling for Organic Crops • 4



Table. Quantities and concentrations of sodium hypochlorite needed to disinfect water for produce cooling,
with a downstream target concentration not to exceed 10 ppm*



Upstream

Concentration target ppm Fl. ozJ5 gal. Cups/50 gal.



Sodium hypochlorite (a.i. 5.25%)


25


0.28


0.25




50


0.55


0.50




75


0.80


0.75




100


1.10


1.00


Sodium hypochlorite (a.i. 12.7%)


25


0.06


0.05




50


0.12


0.10




75


0.17


0.15




100


0.23


0.20



* Organic certification standards permit a maximum of 1 ppm residual chlorine downstream of the product wash step. The specific
crop, water source and quality, water pH, and other factors will influence the total upstream sodium hypochlorite needed to maintain
this target level. A general starting point is 50 ppm for produce with low soil content or minimal tissue damage and cell leakage (such
as from harvest cuts) following harvest. Some products, such as spring mix, may require higher initial upstream chlorination because
the high amounts of organic compounds released from harvest wound sites tie up available hypochlorous acid. This is best deter-
mined in practice and on site with appropriate monitoring equipment or kits, which include titration methods in combination with oxi-
dation-reduction potential (ORP) probes. Background information and sources of monitoring kits and equipment are available from
the UC Postharvest Technology Research and Information Center ( http://postharvest.ucdavis.edu ). Higher levels of sodium
hypochlorite or other chlorinated products are permissible for equipment surface and crate or tote cleaning, provided that treatment
is followed by a thorough clean-water rinse (see Cleaners, Sanitizers, and Disinfectants).



powerful oxidizing treatment and is effective against
chlorine-resistant decay microbes and foodborne
pathogens, acting far more quickly than permissible
concentrations of chlorine. This may be a distinct
advantage for cooling or wash procedures with short
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