(gardening) Postharvest Handling for Organic Crops.pdf

POSTHARVEST HANDLING

FOR ORGANIC CROPS

VEGETABLE

RESEARCH AND

INFORMATION

CENTER

Organic

Vegetable

Production in

California

Series

TREVOR SUSLOW,

UC Cooperative Extension

Vegetable Crops Specialist,

UC Davis

Small Farm

Program

www.sfc.ucdavis.edu

vric.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 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.

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.

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://anrcatalog.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.

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 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

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.

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 (HOCl), 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

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 ) O157: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.

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. oz./5 gal.

Cups/50 gal.

Sodium hypochlorite (a.i. 5.25%)

0.28

0.25

0.55

0.50

0.80

0.75

100

1.10

1.00

Sodium hypochlorite (a.i.12.7%)

0.06

0.05

0.12

0.10

0.17

0.15

100

0.23

0.20

* Organic certification standards permit a maximum of 10 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 Cente r ( 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

contact times. Ozone oxidative reactions create far

fewer disinfection by-products (e.g., trihalomethanes

are a health and environmental concern) than chlorina-

tion. You may decide to use ozonation rather than chlo-

rination in your organic postharvest operation despite

capital and operating costs that are higher than for chlo-

rine or other available methods.

Ozone must be generated on-site at the time of use

and has a very low stability, as short as 20 minutes even

in clear water. Clear water is essential for optimal per-

formance, and adequate filtration of input or recirculat-

ing water is needed. Depending on scale and ozone

generation output, complete-system costs start at about

$10,000. Small-scale units are available for a few thou-

sand dollars and are suitable for limited water use and

small-batch applications. For specifications and installa-

tion, consult an experienced ozone service provider.

Food-grade hydrogen peroxide (0.5 to 1%) and per-

oxyacetic acid are additional options. In general, perox-

yacetic acid (PAA) has good efficacy in water dump

tanks and water flume sanitation applications. PAA has

very good performance, compared to chlorine and

ozone, in removing and controlling microbial biofilms

(tightly adhering slime) in dump tanks and flumes. At

this time, one disadvantage is a higher cost per unit;

another is that availability is restricted to large bulk

units.

CLEANERS, SANITIZERS, AND

DISINFECTANTS

A partial list of allowed cleaners, disinfectants, sanitiz-

ers, and postharvest aides follows.

Acetic acid – allowed as a cleanser or sanitizer. The vine-

gar used as an ingredient must be from an organic

source.

Alcohol (ethyl) – allowed as a disinfectant. Alcohol must

be from an organic source.

Alcohol (isopropyl) – may be used as a disinfectant under

restricted conditions.

Ammonium sanitizers – quaternary ammonium salts are

a general example in this category. Quaternary

ammonium may be used on non-food-contact sur-

faces. Its use is prohibited on food contact surfaces,

except for specific equipment where alternative sani-

tizers significantly increase equipment corrosion.

Detergent cleaning and rinsing procedures must fol-

low quaternary ammonium application. Monitoring

Postharvest Handling for Organic Crops • 5

must show no detectable residue prior to the start of

organic packaging (e.g., fresh-cut salads).

Bleach – calcium hypochlorite, sodium hypochlorite,

and chlorine dioxide allowed as sanitizers for water

and food contact surfaces. In California, product

(fresh produce) wash water treated with chlorine

compounds as a disinfectant cannot exceed 10 ppm

residual chlorine measured downstream of product

contact.

Detergents – allowed as equipment cleaners. This cate-

gory also includes surfactants and wetting agents.

Products must be evaluated on a case-by-case basis.

Hydrogen peroxide – allowed as a water and surface dis-

infectant.

Ozone – considered GRAS (Generally Regarded As

Safe) for produce and equipment disinfection.

Exposure limits for worker safety apply.

Peroxyacetic acid – water disinfectant and fruit and veg-

etable surface disinfectant.

tivities. In eggplant, the cap or calyx is more sensitive

and turns black before the fruit itself is affected. The

effects of chilling injury are cumulative in some crops.

Chilling injury may not be apparent until produce is

removed from low-temperature storage. Depending on

the duration and severity of chilling, chilling symptoms

become evident in the following ways several hours or

a few days after the produce is returned to warmer

temperatures:

• pitting and localized water loss

• browning or other skin blemishes

• internal discoloration

• increased susceptibility to decay

• failure to ripen or uneven color development

• Loss of flavor, especially characteristic volatiles

• Development of off-flavors

Temperature management also plays a key role in

limiting water loss in storage and transit. As the prima-

ry means of lowering respiration rates of fruits and

vegetables, temperature has an important relationship

to relative humidity and thus directly affects the prod-

uct’s rate of water loss. The relative humidity of the

ambient air conditions in relation to the relative

humidity of the crop (essentially 100%) directly influ-

ences the rate of water loss from produce at any point

in the marketing chain. Water loss may result in wilt-

ing, shriveling, softening, browning, stem separation,

or other defects.

Transport to and display at roadside stands or

farmer’s markets often result in extended periods of

exposure of sensitive produce to direct sun, warm (or

even high) temperatures, and low relative humidity.

Rapid water loss under these conditions can result in

limp, flaccid greens and a loss of appealing natural

sheen or gloss in fruits and vegetables. By providing

postharvest cooling before and during transport and a

shading structure during display, you can minimize

rapid water loss at these market outlets.

Approved fruit and vegetable waxes are effective

tools for reducing water loss and enhancing produce

appearance. The uniform application and coverage for

waxes or oils using proper packing line brushes or

rolling sponges is important. Plastic wraps or other

food-grade polymer films retard water loss. Adequate

oxygen exchange is necessary to prevent fermentative

respiration and the development of ethanol and off-

odors or flavors. Wraps or bags must have small perfo-

rations or slits to prevent these conditions, especially

when temperature management is not available. The

exposure of bagged or tightly wrapped produce to

direct sunlight will cause the product’s internal temper-

ature to rise rapidly. Water loss will result and, as cool-

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