Fruit & Vegetable Storage

• I. INTRODUCTION• Proper marketing of perishable commodities such as

fruits and vegetables often requires some storage to balance day-to-day fluctuations between harvest and sale or for long-term storage to extend marketing beyond the end of harvest season.

• Storage of fresh fruits and vegetables prolongs their usefulness and in some cases, improves their quality; it also controls a market glut.

• The principal goal of storage is to control the rate of transpiration, respiration, disease, and insect infestation and to preserve the commodity in its most usable form for the consumer.

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• Storage life can be prolonged by harvesting at proper maturity (Figure 1), control of postharvest diseases, regulation of atmosphere, chemical treatments, irradiation, refrigeration, controlled and modified atmospheres, and by several other treatments.• The main goals of storage are to • (I) slow the biological activity of fruits and

vegetables without chilling injury; • (2) slow the growth of microorganisms, • (3) reduce transpirational losses.

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• A. PRINCIPLES OF STORAGE • Since all fruits and vegetables are living tissues, the

tendency after harvest is to continue respiration. • Thus, proper and adequate storage conditions must be

maintained, otherwise the following undesirable processes may occur in certain vegetables:

1.Sprouting—potatoes, onions, ginger, garlic 2. Elongation—asparagus, carrots, beets,

3. Rooting—due to increased humidity which may result in rapid decay, shrivelling, and exhaustion of food reserves

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4. Greening—exposure of potatoes to light during storage may produce green tissue and synthesis of toxic glycoalkaloids such as solanine and chaconine

5. Toughening—green beans, sweet corn may toughen due to prolonged storage at relatively high temperatures

• The Following factors need to be considered for success of produce storage.

1. Temperature Temperature in a storage room should normally be maintained at the desired temperature for commodities being stored.

Delay in cold storage reduces marketability of fruits and vegetables)

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Temperatures below the optimum range for a given fruit or a vegetable will cause freezing or chilling injuries, temperatures above, depending upon produce, will reduce storage life.

• A wide temperature fluctuation can result in rapid weight and water loss depending upon maturity of produce.

• The USDA Agricultural Handbook number 66 lists recommended storage temperatures and relative humidities for various fruits and vegetables.

• The refrigeration temperature within the recommended range is a result of several important design factors.

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• Temperature variation within the room is minimized by incorporating adequate amounts of insulating material in the walls and by maintaining adequate levels of air circulation in the room.

• When the room is filled, the containers should be stacked to allow an air passage along at least one side of each container.

• Thermostats are placed at a height of five feet from the floor for ease in checking locations.

• A calibrated thermometer should he used to periodically check the thermostat.

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• 2. RELATIVE HUMIDITY • For most perishable fresh fruits and vegetables, the

relative humidity should be maintained between 90 to 95%.

• The relative humidity below this range will result in a moisture loss from the produce (Table 1).

• Thus the produce will be shrivelled and limp. Relative humidity if higher than 90% may cause excessive growth of microorganisms.

• Refrigeration equipment must be especially designed to maintain a higher relative humidity.

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• The environmental factors of temperature, relative humidity and vapor pressure deficit are important in the storage life of fruits and vegetables.

• A 5 to 10% loss in weight of produce results in shrivelling, which makes the produce look stale and unattractive to sell.

• By using high relative humidity during storage, care must be taken to prevent the growth of surface microorganisms

• 3. ATMOSPHERIC COMPOSITION• The atmospheric composition in a storage room is

controlled by addition of gases allowing the commodity to produce or consume gases or by physically or chemically removing undesirable gases from the storage room.

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• Gases such as carbon monoxide (CO), carbon dioxide (CO2), ethylene (C2H4), and nitrogen (N2) can be added to a facility from a bottled supply (or dry ice in the case of C02) or produced by on-site generators.

• As the perishable fruits and vegetables undergo respiration, they consume 02 and release CO2.

• This effect can be successfully used to control the desired concentration of these gases in storage.

• High concentration of undesirable gases are removed by scrubbing devices.

• For example, CO2 can be absorbed in water or lime; • C2H4 and other volatiles can be removed by

potassium permanganate, catalytic oxidation or UV light; and

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• O2 can be removed by using it in a combustion process or by a molecular sieve.

• In certain cases external concentrations of gases are desirable and the accumulated gases can be adjusted by ventilation.

• 4. LIGHT AND OTHER FACTORS• Exposure of potato tubers to light in grocery stores

can synthesize glycoalkaloids (solanine and chalkonine) which are toxic to humans.

• Likewise, other factors such as herbicides, fungicides, pesticides and growth regulators may affect the produce and may have harmful affects on humans.

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B. STORAGE OPERATIONS

• The increase of fruit and vegetable production, owing to large acreage and high-yielding cultivars requires sufficient storage space.

• Accordingly, storage operations have evolved into skilled methods of efficiency with a wide range of variations depending upon the existing facilities, including nature and the variety and quantity of produce to be stored.

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• Storage operations may be either temporary, short-term or long-term.

• Temporary storage operations are needed for highly perishable produce which requires immediate marketing. It may be installed with or without refrigeration.

• Temporary storage is extremely important for roadside stands, gardens, markets, railway stations, shipping yards and retail stores.

• The mid-term storage operation is aimed at checking the market glut without product deterioration.

• This may extend from I to 6 weeks depending upon the need, kind, and maturity of the produce.

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• Mango, banana, papaya, cabbage, eggplant, tomatoes, cauliflower and french bean are transferred to short-term storage rooms, when their quality is still good, and held there until a reasonable market price is attained.

• Fruits and vegetables like apples, oranges, pears, squash, potatoes, sweet potatoes, carrots, onions, garlic, and pumpkins require long- term storage.

• Its operations are mainly influenced by economic factors. The produce is stored during their periods of production, and sold continuously during the rest of the year when producers and dealers can obtain reasonably high prices.

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• Storage operations may be classified as either natural or artificial.

• The natural storage operation keeps the produce in situ without any treatment, whereas artificial storage may be further classified into four types:

(I) mechanical or structural, (2) controlled atmosphere. (3) chemical, and (4) radiation.

• In case of natural storage, the main purpose is to let the fruits or vegetables mature and ripen on plants as long as possible;

• on the other hand, artificial storage operations attempt to provide conditions to prolong the produce quality.

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• 1. Natural Storage• Vegetables such as potato, sweet potato, and

garlic are kept underground for several months. • They are harvested prior to the rainy season for a

better market price. • This harvesting does not involve extra

expenditure and building for storage. • 2. Artificial Storage• Pits or trenches are dug underground for storing

beets, potatoes, onions, carrots, turnips, cabbages, and sweet potatoes where they are covered with straw and soil until there is a market demand (Figures 2 and 3).

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• 3. Ventilated Storage• Cellars are underground rooms with slanting roofs

covered with sods and soils. • The structure may be built into the hillside and

covered with additional soil.• Cellars are provided with heaters and dry

atmospheres during winter months.• Potatoes, turnips, carrots and beets are stored with

high relative humidity at (1 .7—4.4°C). • Where snow is prevalent, a good cellar will

provide satisfactory storage for hard vegetables and fruits. Above-ground warehouses may be used to store produce.

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• In cold weather the produce is covered with blankets to protect from cold temperatures.

• Ventilation is essential for good storage. • Potatoes, onions, garlic bulbs, crucifer leafy

vegetables and fruits are stored successfully.• This storage structure has several advantages over

other types: (I) special construction i not needed; (2) produce is easily handled; (3) grading, storing, packaging of fruits and-

vegetables is facilitated;

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(4) air may be humidified; and (5) fans can be controlled manually or automatically

with a thermostat.• 4. Ice Refrigeration • An advance on the above-ground warehouses was the

use of ice as a refrigerant. • Lower temperatures obtained enable longer storage of

meat and perishable fruits and vegetables. • Ice can be obtained in winter from frozen Lakes and

ponds and stored in ice houses. • The melting of 1 kg of ice absorbs 325 kilojoules.

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• However, removal of melted ice water is a disadvantage.

• The introduction of a small ice box was a great advance on the domestic level, and for small-scale commercial storage of fruits and vegetables.

• II. MECHANICAL REFRIGERATION • Refrigerated storage makes possible the marketing

of perishable fruits and vegetables beyond their harvest season.

• In developped countries, most of the fruits and vegetables are available year-round to consumers.

• This is due to the refrigerated storage.

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• Most storage facilities use mechanical refrigeration to control the desired temperature. This system utilizes the fact that a liquid absorbs heat as it changes to gas

• A common mechanical refrigeration system (Figure 6) uses a refrigerant such as ammonia or freon where vapor can be easily recaptured by a compressor.

• Heat exchange methods of heat transfer play an important part in the refrigeration of fruits and vegetables in maintaining the desired temperature in a refrigerator or a refrigerated warehouse.

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• The refrigerant (ammonia or freon) passes through an expansion valve where its pressure drops and liquid evaporates at temperatures low enough to be effective in removing heat from the storage area.

• Heat needed for evaporation comes from the fruits and vegetables to be cooled.

• Heat is transferred to the product in the storage room and is forced past the evaporator (cooling coils).

• The evaporator is located in the storage room.• The gas is re-pressurized by the compressor and then

passed through a condenser where it is cooled to a liquid.

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• The condenser is located outside the storage area and rejects heat.

• A liquid (ammonia or freon) is stored in the receiver and is metered out as needed to produce an essential or a desired cooling temperature

• The basic equipment and material for mechanical refrigeration are as follows

(I) expansion valve, (2) evaporator, (3) compressor. (4) condenser and (5) refrigerant.

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Areas to consider regarding the refrigerant are • Cost of refrigerant—freons are more expensive than ammonia. • Compatibility—ammonia cannot be used with metals that contain copper. • Toxicity—ammonia even at low concentration can cause injury to fruits and vegetables.

In summary, the basic equipment for mechanical refrigeration consists of compressor, condenser, expansion valve, and evaporator.

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• The refrigerant (ammonia or freon) is compressed, cooled by passing through an air- or water-cooled

condenser, and then expanded through an expansion valve into

evaporator coils. • During this evaporation and expansion phase, heat

is absorbed from fruits, vegetables, and the area to be cooled.

• The absorbed heat is returned for eventual elimination in the condenser.

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• All modem room-refrigeration systems provide forced-air circulation.

• This system uses prefabricated units containing both evaporator coils and blowers for air circulation. They provide excellent storage environment.

• Substantial heat must be removed quickly from the produce in storage;

• it is apparent that greater refrigeration capacity and air velocity must be available.

• A success of mechanical- refrigeration storage rooms depends upon controlled temperature, relative humidity, and air movement.

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• A. TEMPERATURE • Temperature control depends upon a tight, well-

insulated structure and sufficient refrigeration capacity.

• It also depends on the amount and nature of the evaporator-coil surface, its freedom from condensed ice, and the rate of air flowing over the coils. These factors control the total efficiency of refrigeration. B. RELATIVE HUMIDITY

• Relative humidity is the percentage of saturated water vapor at a given temperature.

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• Relative humidity (%) can be determined from psychrometric charts or the basis of wet- bulb and dry-bulb temperatures .

• As the temperature of air increases so does its water-holding capacity.

• Accordingly, air with 90% RH at (21°C) contains much more water than air of the same relative humidity at (4°C).

• As the relative humidity of air decreases, so does its vapor pressure and as vapor pressure decreases, the capacity of the air for removing water from moist sources increases.

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• Thus it is important to maintain a high vapor pressure. If drying is to he avoided, a small vapor pressure differential between stored produce and storage air must be obtained.

• Effective ways of accomplishing this is by rapid equalization of produce and air

temperature, maintenance of high relative humidity in the

storage room air as the produce will tolerate and

no more air movement than is required for even temperature distribution in the refrigerated room.

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• An efficient system for maintenance of high relative humidity is the modification in the construction of the storage room.

• The jacketed storage room is built so that the cooling air circulates around the room in a sealed envelope.

• This maintains uniform temperature and relative humidity. This reduces moisture loss by condensation on the cooling system. In addition, air movement in the room reduces moisture loss from the produce.

• C. AIR MOVEMENT• Air movement must be sufficient enough to remove

respiration heat. It is essential that all parts of the room are subjected to a uniform flow of air.

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• This is accomplished by proper placement of blowers or ducts and stacking of fruits and vegetables to permit free air flow.

• The successful operation of a large refrigeration system requires an efficient control system.

• Microcomputers are presently used to allow precise controls for large warehouse refrigeration systems.

• The defrosting cycle should be set to accomplish the process automatically.

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• The capacity of a refrigeration system is based upon adding all the heat inputs to a storage area. Heat inputs include:

1. Heat conducted through walls, floor, and ceiling. 2. Field and respiration heat of fruits and vegetables. 3. Heat from air filtration. 4 Heat from equipment such as light, fan, forklift, and

personnel moving in and out. • If controlled and modified atmospheres are used in

conjunction with refrigeration, the vapor barrier may serve as a gas bather.

• Hence, special precautions must be taken to insure a gas-tight seal. This operation should be done under the supervision of an experienced refrigeration engineer.

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III. CONTROLLED AND MODIFIED ATMOSPHERE STORAGES

• The principle of storage under high CO2 and low O2 appears to have been applied in ancient times.

• The earliest use of controlled-modified atmospheric storage may be attributed to the Chinese.

• Ancient Chinese writings reported that litchi fruits were transported from northern China to southern China in sealed clay pots to which fresh leaves and grass were added.

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• It may be surprised that during the 2-week journey, respiration of the fruits, leaves, and grass generated a high-carbon dioxide—low-oxygen atmosphere in the pots which retarded ripening of the litchis.

• The first scientific observations of the effects of atmosphere on fruit ripening were made in 1819-20 by Berard, a Professor of Chemistry at Montpelier Institute in France.

• Several further independent studies of the effects of controlled atmospheres on fruit ripening were made in the United States.

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• One study involved the construction of a primitive controlled-atmosphere store in which apples were successfully stored.

• However, it was not until the work of Kidd and West at the Low Temperature Research Station at Cambridge, England that a sound basis of the controlled-atmosphere storage of produce was established in 1927.

• During the last sixty years, the effects of controlled, modified atmospheres—hypobaric storage— have been extensively studied on fresh fruits arid vegetables (Tables 2 and 3).

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• Controlled and modified atmosphere storages (MA and CA) indicate the removal or addition of gases resulting in an atmosphere composition for fruits and vegetables and their products that is different that of air (75% N2, 21% O2 and 0.03% CO2) .

• MA and CA differ in the degree of control;

• CA is more exact than MA.

• In MA gases are not controlled at specific concentration.

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• CA: CA when combined with refrigeration, retards respiration of fruits and vegetables,

• delay softening, yellowing spoilage and other breakdown processes by maintaining an atmosphere with more CO2 and less O2 than in normal air.

• CA is utilized now on commercial scale, and more than 50% of the US apples and Palestinian oranges are stored under CA condition.

• Tables 1 and 3 shows the different type of storage for some fruits and vegetables.

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• Storage terms: • many terms are used in the field of fruits and

vegetables storage. • Some of there terms like refrigerated storage, CA

and MA storage has been covered. • Additionally, MA includes the packaging in film

bags that requires a decrease in O2 and increase in CO2 or N2 but without precise control.

• Gas storage is another term sometimes used to

differentiate between CA or MA and air storage.

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• However if one gas is only used, in such cases the storage is named with that gas like CO2 storage, N2 storage…etc.

• Vacuum storage, hypobaric storage or sub- atmospheric pressure storage are names for one type of storage which is a type of CA storage.

• It refers to the storage of fruits and vegetables under control atmosphere storage in addition to maintaining a low pressure on the produce which will result in more extending shelf life by diffusion of ethylene from the tissues by evacuation.

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• Metabolic effect of CA : • many studies showed that CA may have the

following effects on the stored fruits and vegetables:

retard respiration, cause acid accumulation and acetaldehyde

formation, increase sugars, decrease alcohol soluble and protein N, causes pectin changes and inhibit chlorophyll degradation.

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• Adverse and toxic effects of CA: • controlled atmosphere storage has great

advantages and can have some adverse effects on fruits and vegetables.

• High levels of CO2 and low concentration of O2 (tables 4 and 5) may cause:

Decay internal browning, breakdown and accumulation of some organic acids such as

succinic acid of toxic levels (0.001 M).

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• Physiological effects of high CO2 level:• higher levels of CO2 during CA storage of fruits and

vegetables may have some effects on ripening, enzyme activity, production of volatile, metabolism of organic acids, breakdown of pectic substances, chlorophyll synthesis and fruit degreening and types and proportions of present sugars.

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• Higher levels of CO2 also alters the climacteric pattern in fruits and vegetables, produces off-flavors, increase the PH and reduce ascorbic acid content, retards fungal growth, affects C2H4 production or function and may cause (high level of O2) some physiological

disorders like brown heart and scald.

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• Humidity and C2H4 control during CA storage:

• it is also recommended to control both C2H4 and humidity during CA storage of fruits and vegetables in addition to controlling of O2 and CO2 and temperature.

• Accumulation of C2H4 will cause degreening and ripening of fruits and vegetables, so absorption of C2H4 by KMNO4 is advised.

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• Also in commercial CA storage humidity reaches to saturation in storage of some fruits and vegetables and this may encourage the growth of fungi.

• As a result it is advised to apply a suitable fungicide to retard the fungi growth.

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• Behavior of fruits and vegetables after CA storage:

• after the removal of fruits and vegetables from CA storage, they may have some change like

increased respiration rate, appearance of tissue browning and decease in

firmness. • However, many investigation noticed that the

organoleptic properties of fruits and vegetables after CA storage is more better than those after refrigerated storage provided that the CA conditions were properly selected.

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• CA storage duration (long or short): • CA storage for a long time may cause injuries to

fruits and vegetables inspite of the properly selected conditions.

• However, storage life of fruits and vegetables in CA storage may be 50% longer than in air storage.

• Results regarding the CA storage for short time are of vital importance specially to be applied in transportation.

• The effect of different levels of O2 or/and CO2 during CA storage for short time for some fruits and vegetables have been studied but further research is needed.

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• Including of CO in CA storage was found to be beneficial especially with regard to control fungal decay and to inhibit discoloration (5-10% concentration).

• Advantages and disadvantages of CA and MA storage:

• the advantages or benefits include retardation of senescence, reduction of produce sensitivity to C2H4, controlling some of the physiological disorders like

chilling injury and also controlling postharvest disease and decaying.

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• The limitations or disadvantages include increasing some of the postharvest disorder like sprouting in

potatoes, brown heart in apples; irregular ripening of bananas and tomatoes, development of off-flavor and in some cases increasing the susceptibility to decay.• Something of interest in CA storage that there is no single

best combination of CO2 and O2 for mixed storage of fruits and vegetables.

• Instead each species and may be each cultivar varies in its CA requirements.

• Tables 6 and 7 show the CA requirements from O2 and CO2 for some of the important fruits and vegetables..

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• Storage in polymeric films:

• great progress has been achieved in the field of developing a produce package for CA storage.

• These packages are perforated and semipermeable and aim at

reducing moisture loss, protect the produce from mechanical damage and

improve its appearance.

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• In the produce package, respiration occurs by the produce and permeation by the package.

• In other words the produce takes up O2 and gives CO2, H2H4 and volatiles while the package according to its permeability permit the escape of these gases.

• However, the package system should be in such a way to achieve steady state condition where equilibrium concentration of O2 and CO2 is reached.

• Many factors interfere or affect this steady conditions such as

the type of produce, its weight,

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variety, respiration rate, stage of maturity, temperature, O2 and CO2 level needed, C2H4 concentration, light, film thickness, film permeability and others.

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• However, all these factors should be considered in selecting the proper package for any given fresh produce.

• Due to the complexity of controlling such large variable, the computer has been utilized for such purposes and a good results have been achieved.

• It is also of value to note that packaged apples have a longer shelf life than control apples with about two months.

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• Vacuum storage:

• it may be classified to two types: the first include the gas-flush packaging where the

air in the package is replaced by another gas such as CO2 or N2 and it is used for packaging of salads, fruits juices and minimally processed fruits and vegetables,

the second type is that where all air is removed and a vacuum is created.

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• High density polyethylene films are used for this purpose and this packaging technique is utilized for minimally processed fruits and vegetables.

• Something to be considered here is to leave some O2 in the package for normal respiration and the packaged produce should be stored at 5C or under refrigeration to avoid deterioration.

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• Sub atmospheric (low pressure or hypobaric) storage:

• the storage life of many fruits and vegetables can be extended by reduced pressure under refrigeration due to low respiration rate and evacuation of C2H4.

• However, the hypobaric storage is a form of CA storage.

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• Regarding the principles of hypobaric storage; the produce is placed at a given temperature in a sealed container and a constant sub atmospheric pressure is maintained by continuous evacuation;

• the produce is ventilated by air saturated with water vapor and containing suitable fungicides in some cases.

• It is of interest to note that at lower pressure storage such as 278 mm Hg or less, microorganism growth retardation is achieved.

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• Radurization: • it is meant by this term the utilization of ionizing

radiation materials such as cobalt, cesium and uranium is utilized.

• Only beta and gamma radiation kinds are utilized in food preservation;

• beta radiation is used for food pasteurization and in the case of gamma radiation, it is utilized for food sterilization.

• Retardation of sprouting and rooting by radiation are practiced commercially.

• In case of pasteurization a dose of 1 megarad is utilized, while for sterilization a dose higher than 1 Mrad is used.

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Future of Modified Atmosphere Research

• A.A. Kader• Department of Plant Sciences• University of California• One Shields Avenue• Davis, CA 95616, USA• Keywords: controlled atmospheres, flavor quality,

fruits, vegetables• Proc. IXth Intl. Contr. Atmos. Res. Conf.• Ed.: R.M. Beaudry• Acta Hort. 857, ISHS 2010

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Abstract

• It is not possible to discuss the future of modified atmosphere (MA) research without considering the broader aspects of research aimed at maintaining quality of fresh horticultural perishables between harvest and consumption.

• Providing better flavored fruits and vegetables is likely to increase their consumption, which would be good for the producers and marketers (making more money or at least staying in business) as well as for the consumers (increased consumption of healthy foods).

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• To achieve this goal, we and all those involved in producing and marketing fruits and vegetables need to:

(1) replace poor flavor cultivars with good flavor cultivars from among those that already exist and/or by selecting new cultivars with superior flavor and good texture;

(2) identify optimal cultural practices that maximize flavor quality, such as optimizing crop load and avoiding excess nitrogen and water.

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(3)encourage producers to harvest fruits at partially-ripe to fully-ripe stages and

vegetables at their optimal maturity stages by developing handling methods that

protect these commodities from physical damage; (4) identify optimal postharvest handling conditions

(time, temperature, relative humidity, atmospheric composition) that maintain flavor quality of fruits and vegetables and their value-added products.

• Postharvest-life should be determined on the basis of flavor rather than appearance.

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• The end of flavor-life results from losses in sugars, acids and aroma volatiles (especially esters) and/or development of off-flavors (due to fermentative metabolism or odor transfer from fungi or other sources);

(5) develop ready-to-eat, value-added products with good flavor; and

(6) optimize maturity/ ripeness stage at the time of processing and select processing methods to retain

good flavor of the processed products. • Future modified atmosphere research can be part of

research on strategies number 4, 5 and 6 listed above.

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• Continued improvements in polymeric films and other packaging materials will facilitate expanded use of MA packaging to extend

postharvest-life of fresh-cut fruits and vegetables and permit their distribution via vending machines.

• More cost-effective methods for establishing and maintaining MAs will facilitate their use during storage at shipping points, transportation and storage at destination points.

• Maintaining the MA chain is the second most important factor after the cold chain in keeping quality and safety of fresh produce

between harvest and consumption.

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• Further evaluations are needed of: • (1) the synergistic effects of MA and the ethylene-

action-inhibitor,1-methylcyclopropene, on delaying ripening of partially-ripe climacteric fruits and senescence of vegetables ;

• (2) MA as a component of postharvest integrated pest management (decay and insect control);

• (3) MA in relation to food safety considerations; and (4) the biological bases of MA effects on fresh horticultural perishables.

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TRENDS IN MARKETING FRESH PRODUCE

• Current trends that are expected to continue in the future include globalization of produce marketing, consolidation or formation of alliances among producers and marketers from various production areas, consolidation of retail marketing organizations and increased demand for year round supply of many produce items with better flavor.

• Maintaining the cold chain and the modified atmosphere chain when needed are very important to globalization of produce marketing.

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• For some commodities (such as apples, pears and kiwifruits), a year round supply from northern and southern hemisphere countries eliminates price incentives to domestic producers for “out-of-season” produce.

• This reduces the need for CA storage beyond 6 or 7 months in either hemisphere and has the potential of providing the consumers with better flavor-quality fruits.

• Also, there will be opportunities for using available CA storage facilities to store fruits from the other hemisphere (that are transported under optimal CA conditions) after the end of storage of locally produced fruits.

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FLAVOR QUALITY OF FRUITS AND VEGETABLES

• It is not possible to discuss the future of modified atmosphere (MA) research without considering the broader aspects of research aimed at maintaining quality of fresh horticultural perishables between harvest and consumption.

• Flavor attributes and associated constituents include sweetness (sugars), sourness or acidity (acids), astringency (tannins), bitterness (isocoumarins), aroma (odor-active volatile compounds), off-flavors (acetaldehyde, ethanol, and/or ethyl acetate above certain concentrations) and off-odors

(sulfurous compounds above certain concentrations).

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• Nutritional quality of fruits and vegetables is determined by their contents of vitamins, minerals, dietary fiber and antioxidant phytochemicals, such as carotenoids and flavonoids.

• It is important to determine the effects of modified atmospheres during postharvest handling on these constituents as indicators of flavor and nutritional quality of intact and fresh-cut fruits and vegetables.

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• Providing better flavored fruits and vegetables is likely to increase their consumption, which would be good for the producers and marketers (making more money or at least staying in business) as well as for the consumers (increased consumption of healthy foods).

• To achieve this goal, we and all those involved in producing and marketing fruits and vegetables need to do the following:

• 1. Replace poor flavor cultivars with good flavor cultivars from among those that already exist and/or by selecting new cultivars with superior flavor and good textural quality.

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• 2. Identify optimal cultural practices that maximize flavor quality, such as optimizing crop load and avoiding excess nitrogen and water, which along with low calcium shorten the postharvest-life of the fruits and vegetables due to increased susceptibility to physical damage, physiological disorders and decay.

• 3. Encourage producers to harvest fruits at partially-ripe to fully-ripe stages and harvest vegetables at their optimal maturity stages by developing handling methods that

protect these commodities from physical damage.

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• 4. Identify optimal postharvest handling conditions (time, temperature, relative humidity, atmospheric composition) that maintain flavor quality of fruits and vegetables and their value-added products.

• Postharvest-life should be determined on the basis of flavor rather than appearance.

• Most of the published estimates of postharvest-life under modified or controlled atmospheres are based on appearance (visual) quality, and in some cases, textural quality.

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• These estimates should be revised to reflect the

end of flavor-life when the product looks good but does not taste good.

• The end of flavor-life results from losses in sugars, acids and aroma volatiles (especially esters) and/or development of off-flavors (due to fermentative metabolism or odor transfer from fungi or other sources).

• The possible role of modified atmospheres in delaying these undesirable changes should be investigated.

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• 5. Develop ready-to-eat, value-added products with good flavor. A very important research area is to find the optimal atmospheres for delaying browning and softening of fresh-cut products during distribution within the optimal ranges of temperature and relative humidity.

• 6. Optimize maturity/ ripeness stage at the time of processing and select processing methods to retain good flavor of the processed products.

• Future modified atmosphere research can be part of research on strategies number4, 5 and 6 listed above.

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MAINTAINING THE MA CHAIN

• Continued improvements in polymeric films and other packaging materials will facilitate expanded use of MA packaging to extend postharvest-life of fresh-cut fruits and vegetables and permit their distribution via vending machines and quick-service restaurants.

• MAP is an effective way to maintain the desired atmospheric composition between shipping point and the consumer’s home.

• When evaluating polymeric films, it is important to place the control product in perforated plastic bags to separate the effect of the film on reducing water loss from its effect as a barrier to carbon dioxide and oxygen diffusion.

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• Instead of developing more models for MAP, researchers are encouraged to

• build upon existing models and improve their accuracy.

• Although much research has been done on the use of surface coatings to modify the atmosphere within many commodities, this technology has not been used to any extent because of the variability in composition among batches of the coating material.

• When combined with the natural variation in the gas diffusion characteristics among individual commodity units, a portion of each lot is lost due to off-flavors caused by fermentative metabolites.

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• Further research is needed to overcome these constraints to use of surface coatings for modification of internal atmospheres of fruits and vegetables.

• More cost-effective methods for establishing and maintaining MAs will facilitate their use during storage at shipping points, transportation and storage at destination points.

• Maintaining the MA chain is the second most important factor after the cold chain in keeping quality and safety of fresh produce between harvest and consumption.

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COMBINED EFFECTS OF MA AND 1-MCP

• Further evaluations are needed of the synergistic effects of MA and the ethyleneaction-inhibitor,

1-methylcyclopropene, on delaying ripening of partially-ripe climacteric fruits and senescence of vegetables and deterioration (browning and softening) of fres-hcut products.

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MA FOR DECAY AND INSECT CONTROL

• More research is needed to evaluate the efficacy of MA as a component of postharvest integrated pest management (decay and insect control) in fresh horticultural perishables.

• The fungistatic and insecticidal effects of low oxygen, elevated carbon dioxide and superatmospheric oxygen MA alone or in combination with other treatments merit further investigation.

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MA AND FOOD SAFETY CONSIDERATIONS

• More research is needed to quantify the effects of MA on growth of pathogenic bacteria on fresh produce and on production of mycotoxins by fungi.

• Also, we need to understand how do high oxygen concentrations alone or in combination with elevated carbon dioxide concentrations influence growth of decay-causing bacteria and fungi and of human pathogens?

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BIOLOGICAL BASES OF MA EFFECTS

• Studies of the biological bases of MA effects on fresh horticultural perishables should be expanded to include superatmospheric oxygen concentrations and their

interactions with elevated carbon dioxide levels.• RETURN ON INVESTMENT OF MA• Future expansion in the commercial use of MAP, MA during

transport and CA storage will depend on demonstrating a positive return on investment (ROI).

• Thus, it is important to estimate the ROI of every application before recommending its use.

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Selected References

• Al-Ati, T. and Hotchkiss, J.H. 2003. The role of packaging film permselectivity in modified atmosphere packaging. J. Agric. Food Chem. 51:4133–4138.

• Amarante, C. and Banks, N.H. 2001. Postharvest physiology and quality of coated fruits and vegetables. Hort. Rev. 26:161–238.

• Beaudry, R.M. 2000. Responses of horticultural commodities to low oxygen: limits to the expanded use of modified atmosphere packaging. HortTechnology 10:491–500.

• Blankenship, S.M. and Dole, J.M. 2003. 1-Methylcyclopropene: a review. Postharvest Biol. Technol. 28:1–25.

• Brecht, J.K., Chau, K.V., Fonseca, S.C., Oliveira, F.A.R., Silva, F.M., Nunes, M.C.N. and Bender, R.J. 2003. Maintaining optimal atmosphere conditions for fruits and vegetables throughout the postharvest handling chain. Postharvest Biol. Technol.

27:87–101.

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• Burg, S.P. 2004. Postharvest physiology and hypobaric storage of fresh produce. CABI publishing, Wallingford, UK, p.654.

• Fonseca, S.C., Oliveira, F.A.R., Lino, I.B.M., Brecht, J.K. and Chau, K.V. 2000.

• Modelling O2 and CO2 exchange for development of perforation-mediated modified atmosphere packaging. J. Food Eng. 43:9–16.

• Gross, K., Wang, C.Y. and Saltveit, M.E. (eds.). 2004. The commercial storage of fruit, vegetables, and florist and nursery stocks. USDA Agr. Handbk. 66 (includes chapters on controlled atmosphere storage and modified atmosphere packaging). Available online at: http://www.ba.ars.usda.gov/hb66/index.html .

• Hagenmaier, R.D. 2005. A comparison of ethane, ethylene, and CO2 peel permeance for fruit with different coatings. Postharvest Biol. Technol. 37:56–64.

• Kader, A.A. (Ed.). 2001. CA Bibliography (1981-2000) and CA Recommendations (2001), CD. University of California, Postharvest Technology Center, Postharvest

• Horticulture Series No. 22 (The CA Recommendations, 2001 portion is also available in printed format as Postharvest Horticulture Series No. 22A). For more information, go to: http://postharvest.ucdavis.edu

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• Kader, A.A. 2003a. Physiology of CA treated produce. Acta Hort. 600:349–354.

• Kader, A.A. 2003b. A perspective on postharvest horticulture (1978–2003). HortScience 38:1004–1008.

• Kader, A.A. and Ben-Yehoshua, S. 2000. Effects of superatmospheric oxygen levels on postharvest physiology and quality of fresh fruits and vegetables. Postharvest Biol. Technol. 20:1–13.

• Kader, A.A. and Watkins, C.B. 2000. Modified atmosphere packaging-toward 2000 and beyond. HortTechnology 10:483–486.

• Lange, D.L. 2000. New film technologies for horticultural products. HortTechnology 10:487–490.

• Mattheis, J.P. and Fellman, J.K. 2000. Impacts of modified atmosphere packaging and controlled atmosphere on aroma, flavor, and quality of horticultural commodities.HortTechnology 10:507–510.

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• Mitcham, E.J. 2003. Controlled atmospheres for insect and mite control in perishable commodities. Acta Hort. 600:137–142.

• Oosterhaven, J. and Peppelenbos, H.W. (Eds.). 2003. Proceeding of the Eighth International Controlled Atmosphere Research Conference. Acta Hort. 600:1–838 (2 volumes).

• Pesis, E. 2005. The role of the anaerobic metabolites, acetaldehyde and ethanol, in fruit ripening, enhancement of fruit quality and fruit deterioration. Postharvest Biol. Technol. 37:1–19.

• Saltveit, M.E. 2003. Is it possible to find an optimal controlled atmosphere? Postharvest Biol. Technol. 27:3–13.

• Schotsmans, W., Verlinden, B.E., Lammertyn, J. and Nicolai, B.M. 2003. Simultaneous measurement of oxygen and carbon dioxide diffusivity in pear fruit tissue. Postharvest Biol. Technol. 29:155–166.

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• Soliva-Fortuny, R.C. and Martin-Belloso, O. 2003. New advances in extending the shelflife of fresh-cut fruits: a review. Trends Food Sci. Technol. 14:341–353.

• Suppakul, P., Miltz, J., Sonneveld, K. and Bigger, S.W. 2003. Active packaging 217 technologies with an emphasis on antimicrobial packaging and its applications. J. food Sci. 68:408–420.

• Veltman, R.H., Verschoor, J.A. and Ruijsch-van Dugteren, J.H. 2003. Dynamic control system (DCS) for apples (Malus domestica Borkh cv ‘Elstar’): optimal quality through storage based on product response. Postharvest Biol. Technol. 27:79–86.

• Watkins, C.B. 2000. Responses of horticultural commodities to high carbon dioxide as related to modified atmosphere packaging. HortTechnology 10:501–506.

• Watkins, C.B. and Miller, W.B. 2005. A summary of physiological processes or disorders in fruits, vegetables and ornamental products that are delayed or decreased, increased, or unaffected by application of 1-methylcyclopropene (1-MCP). Available online at:

• http://www.hort.cornell.edu/mcp/ethylene.pdf

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