1Introduction

Elhadi M. Yahia

CONTENTS1.1 Introduction 11.2 History 31.3 Gases Used 61.4 Biological Basis of MAjCA Effects 61.5 Potential Detrimental Effects 71.6 Technological Applications 8

1.6.1 Storage 81.6.2 Transport 91.6.3 Packaging 11

1.7 Some Additional Treatments 121.8 Some Future Research Needs 131.9 Conclusions 13References...................................................................................................................................... 14

1.1 Introduction

Modified atmosphere (MA) refers to any atmosphere different from the normal air (20%-21%O2, about 0.03% C021 about 78%-79% N2I and trace quantities of other gases), whllecontrolled atmosphere (CA) refers to atmospheres different than normal air and strictIycontrolled during all time. MA and CA usually involve atmospheres with reduced O2andjor elevated COz levels. Hypobaric (low pressure) storage is a CA system involvingthe use of vacuum to reduce the partíal pressure of the gas component of air (Burg, 2004;Yahia, 2004).

The techn9logies of MA and CA are widely used for the storage, transport and pack-aging of several types of foods. They offer several advantages such as delay of ripenmg andsenescence of horticultural commodities, control of some biological processes such asrancidity, insects, bacteria and decay, among others. MA and CA combined with precisiontemperature management allow nonchemical insect control in some commodities formarkets that have restrictions against pests endemic to exporting countries and for marketsthat prefer organic produce (see Chapter 11).

Major developments have been accomplished in the last two to three decades, suchas better construction of sealed storage roorns (see Chapter 2) and transport containers(see Chapter 3), better gas monitoring and control systerns, and new packaging systerns(see Chapters 4 and 5). Optimum atmosphere for different types of foods is very variable,

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2 Modified and Controlled Atmospheres lntroduction

TABLE 1.1

MAandCA,;'ies ago. Thi$plant orgvegetables .from freez'modifiedused to a"with very Ci

and more sstorage ofroot crops,citrus in the.cated storaglthe cost C'practicedextreme,useofpolprovide astaple food

Accordingconducted'PharmacyproducedOprunes, and,up to aboutafter reoxygen. BePhysiqueother scien"cation by th,

The firstNorthemOsheet metal-maintain aApples were,up to 9 motechnology.be commercithe 1890swi'.grapes in w.during shipand may betransport of

forfreshhoaspects of bi,distribution .

Commodities

Almond, Brazil nut, cashew, filbert, macadamia, pecan, pistachio, walnut, driedfruits, and vegetables

50me cultivars of apples and European pearsCabbage, Chinese cabbage, kiwifruit, persimmon, pomegranate, and some cultivarsof Asian pears

Avocado, banana, cherry, grape (no 502), mango, olive, omon (sweet cultivars),some cultivars of nectarine, peach and plum, and tomato (mature-green)

Asparagus, broccoli, cane berries, fig, lettuce, muskmelons, papaya, pineapple,strawberry, sweet com, fresh-cut fruits, and vegetables

Saurce: From Kader, A.A. 1986. Faad Technalagy, 40, 99,102.

1

>12

1-3

6-123-6

Classification of Fruits and Vegetables According to Their eA Storage Potentialat Optimum Temperatures and Relative Humidities

Range of StorageDuration (Months)

and depends on many factors such as type of product, purpose of use, physiological age,holding temperature, and duration of treatment (see Chapters 12 through 20). Exposure ofdifferent types of foods (especially horticultural products) to 02levels below, andjor cazlevels above their optimum tolerable range can cause the initiation andjor aggravation ofcertain physiological disorders, irregular ripening, increased susceptibility to decay, devel-opment of off-flavors, and could eventually cause the loss of the product (see Chapters 8and 9). Most horticultural crops can tolerate extreme levels of gases when stored for onlyshort periods (Yahia, 1998a,b, 2004).

MA and CA should always be used as a compliment and never as a substitute forproper handling techniques, especially optimum temperature and relative humidity (RH).CA storage has been restricted mainly to apples, pears, kiwifruit, and cabbage. MA andCA for transport are used for many horticultural commodities. Modified atmospherepackaging (MAP) is used for some intact and minimally processed fruits and vegetables,in addition to some other types of foods such as meat, poultry, fish and sea foods, cheeseand some other milk products, prepared foods, dry and dehydrated foods, coffees,among others.

Commercial interest in the development and implementation of MAjCA for transpor-tation, storage, and packaging of fresh horticultural commodities (Table 1.1)will stimulateresearch in these areas. Economic principIes of supply and demand for the commodityin relation to energy use, cost, benefit, and practicality will ultimately determine the useof MAjCA for postharvest maintenance of horticultural commodities (see Chapter 21).Continued technological developments in the future to provide MAjCA during storage,transport, and packaging at a reasonable cost are essential to greater applications on freshhorticultural commodities and their products (see Chapter 23).

There are basic biologically defined limits to environment that can be employed for thepostharvest preservation of fresh horticultural commodities. The basic processes of tran-spiration, respiration, and biochemical transformations may continue in much the samemanner in plant tissues after harvest as before harvest. However, this is done withoutreplenishment of reserves or metabolic control from the parent plant. The nature of thesecellular processes can be altered, and the chemical reaction rate can be attenuated orstimulated by manipulating the temperature and concentration of the biologically activegases such as water vapor, Oz,caz, and ethylene among others. Beyond certain limits oftemperature and gas atmosphere composition and according to the nature and stage ofdevelopment of the commodity, physiological disorders may develop, which terminate theusefullife of the commodity by destroying appearance, flavor, nutritive value, or whole-someness. Development and application of successful postharvest preservation techniques

for fresh horticultural commodities depends largely on understanding certain fundamentalaspects of biology, engineering, and economics that are important in the maintenance anddistribution of these perishables (see Chapter 22).

1.2 History

MA and CA as techniques for postharvest preservation of foods originated several centur-ies ago. This was long before the role of Oz and caz in the basic respiration of plants andplant organs was understood. The centuries-old tradition of burying certain fruits andvegetables in the ground after enclosing them in various wrappings and protecting themfrom freezing by covering them with soil and insulating materials is an example of amodified environment for extending the life of some types of foods. This practice is stillused to a limited extent and most probably will continue in the future, especially in regionswith very cold winters. Other examples of subterranean storage to benefit from reducedand more stable temperatures, and modified gas atmosphere include the practice of cavestorage of fruits and vegetables as done in China and Turkey, and trench storage of grains,root crops, and silage. Cave storage of apples and pears is still practiced in China, andcitrus in the region of Cappadocia in Turkey, and the results of this relatively unsophisti-cated storage technology rival those obtained by modem means and at only a fraction ofthe cost (Dilley, 2006). Several countries (especially developing countries) have longpracticed the storage of grains and root crops in huts and pits to protect them fromextreme, unstable weather conditions and from infestation of insects and rodents. Theuse of polymeric films and synthetic rubber and metalliners is being adopted as a means toprovide atmospheric modification to further extend the useful storage life for some of thestaple food and feedstocks (Dilley, 2006).

According to Dalrymple (1969), the first recorded scientific study of CA storage wasconducted in the early 1800s in France by Jacques Etenne Berard, a chemist in the School ofPharmacy at Montpellier. His studies revealed that harvested fruits utilized Oz andproduced caz, and fruits kept in an atmosphere devoid of oxygen did not ripen. Peaches,prunes, and apricots were found to be stored for up to 1 month, and apples and pears forup to about 3 months at room temperature. Moreover, he found that the fruit would ripenafter retuming them to air, providing that they were not kept too long in storage withoutoxygen. Berard's studies published in 1821 won him acclaim and the Grand Prix dePhysique from the French Academy of Science. These studies apparentIy stimulatedother scientists to conduct similar investigations, some of which are reviewed in a publi-cation by the u.s. Department of Agriculture (Bigelow et al., 1905).

The first recorded studies on MAjCA of fruits in the United States were made inNorthem Ohio by Benjamin Nyce in about 1865 (Dilley, 1990). He constructed an airtightsheet metal-lined storage room of about 4000 bushel capacity that was cooled with ice tomaintain a storage temperature of just above the freezing point of water (Dilley, 2006).Apples were stored commercially at the Cleveland storage in saleable condition for periodsup to 9 months following harvest, and Nyce obtained several U.S. patents on his storagetechnology. A subsequent CA storage facility built by Nyce in New York did not prove tobe commercially acceptable. The San Jose Fruit Company in California conducted tests inthe 1890s with railcar shipments of peaches, nectarines, pears, quinces, persimmons, andgrapes in which nomefrigerated railcars were sealed and gassed with carbon dioxideduring shipment of produce from California to Chicago. The tests had partial successand may be considered the forerunner of what subsequently has become known as MAtransport of perishables. Shipments of peaches, plums, and pears were made for several

,...lntroduction 3

• 11

',j

an existing ~expansion in •mid-1950s, w~construction dstoring appl~and labor savJfruit were imJ(Dilley, 2006).)

Overholserland McKinndvariety to be'fruits were sofKiddandwasfound tolargelye" .and was resogy (Dilley,investigatioand Smock, ~the late 193 .technology .commercialiand pears injCanada Dep .'.Nova Scotia,1959, 1960, 1

MA andcommodities'cranberries .established .before beingcommercialNova Scotia>storage roafoIlowed byYork StateNew Yorkwhere CA st,regions (DiandCanadain the 1960simprovemen:Delicious apof apples anllate 1980s,e2006). CA ssuch as sev,1980), Chile;when shipsincreasingshipping of

lntroductioniModified and Controlled Atmospheres

years, although some success was seen only in pears. The practice of carbon dioxideemichment of the transport of perishables was reinstated as a supplement to refrigerationin the 1960s. Strawberries and sweet cherries show beneficial effects from carbon dioxideemichment of the atmosphere during transport. These early trials with CA or MA storageand transport of perishables, although encouraging, indicated a high level of risk ofproduce loss, which probably was a factor in slow commercial acceptance of these practices(Dilley, 2006). Major scientific research is sti11needed to adequately establish MA and CAfor transport.

Scientists at Washington State University conducted some of the earliest reported studieson the effects of the gaseous environment on ripening of apples (Dilley, 2006). The resultsof these investigations, which were conducted in 1903 and 1904, were eventually publishedby Thatcher (1915). They made the important observation that carbon dioxide was aninhibitor of the ripening process, and 60 years would pass before Burg and Burg (1965)elucidated the mechanism of the carbon dioxide effect as competitive inhibition of ethyleneaction on ripening. Hill's studies (described by Thatcher) also implicated the possible roleof enzymes on the basic respiration of apples during ripening. Again, nearly 60 yearswould pass before studies at Michigan State University showed that protein synthesis andenzyme activity were closely linked to the ripening process of apples (Frenkel et al., 1968).This was confirmed by the investigations of Hulrne and coworkers at the Ditton Labora-tory in England (Hulme et al., 1968). In the early 1900s, Hi11(1913) at Comell Universitymade the observation that ripening of peaches could be slowed by storing them in carbondioxide and, to a lesser extent, in other inert gases. The beneficial effects were ostensiblyachieved by restricting the availability of oxygen. This confirmed, to some extent, theobservations made at San Jose Fruit Company noted earlier. Hill also made the interestingobservation that the respiration rate of peaches exposed to carbon dioxide did not retum tothe prestorage level. The U.S. Department of Agriculture renewed investigations on theeffects of carbon dioxide on storage life and respiration of apples in conjunction withstudies on superficial scald of apples (Brooks et al., 1919).

The work that led to the commercial application of CA storage was laid by Franklin Kiddand Cyril West, working at the Low Temperature Research Station at Cambridge, England.They began a systematic study of fruit respiration and ripening as influenced by tempera-ture, caz, and Oz under the auspices of the Food Investigation Board of the u,K. Depart-ment of Scientific and Industrial Research. These studies, published over a period spanningnearly 40 years (Kidd and West, 1927a,b, 1930, 1937, 1950), provided the basis for much ofthe CA storage technology in use today (Dilley, 2006). Their initial studies done on pomefruits and berries have been reviewed by Fidler et al. (1973), where emphasis was directedon apples, but later also included work on bananas, pears, and oranges. Their research wascontinued at the Ditton Laboratory, which was constructed in 1930 on the grounds of theEast MaIling Research Station in Kent, England, where a portion of the main building wasconstructed as a replica of the hold of a ship, presumably to address the problems oftemperature and gas atmosphere maintenance encountered during maritime transport offruits from the Commonwealth countries to England (Dilley, 2006). Fidler and coIleaguesalso conducted CA storage research at the Ditton and Covent Gardens Laboratories, andcontributed toward current-day recommendations for the CA storage of various varietiesof apples and pears grown in the United Kingdom. The first commercial apple storage toemploy the "gas storage" technique in England was constructed in 1929 near Canterburyin Kent County. The commercial success of this venture was realized in 1930 and led torapid expansion in the adoption of gas storage technology for apples and pears in thedecade of the 1930s (Dilley, 2006).

The first commercial CA storage in Michigan was established in Kent County, Michigan,in the early 1950s (Di11ey,2006). This was done by providing a gas-tight sheet metalliner in

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an existing mechanically refrigerated apple storage, which provided most of the earlyexpansion in CA storage volume in the United States and Canada. It was not until themid-1950s,when the practice of using bulk bins and lift trucks was introduced, that newconstruction of CA storages with high ceilings began rapidly replacing the practice ofstoring apples and pears in 1 bushel field crates. The increased efficiency in fruit handlingand labor savings afforded by the use of bulk bins for harvesting, handling, and storing offruit were important factors in the growth of CA storage capacity worldwide since 1950(Dilley,2006).

Overholser (1928)and Biale (1942),investigated CA storage of avocados. In 1935,Allenand McKinnon found that CA storage of Yellow Newton apples at 3°C-4°C allowed thisvariety to be stored successfully, avoiding low-temperature disorders found when thefruits were stored in air at O°C-l°C (Dilley, 2006).This confirmed the earlier observationsofKidd and West (1927a)with several important English apple varieties where storage lifewas found to be limited by low-temperature or chilling injury disorders and these could belargelyeliminated by gas storage at 3°C-4°C.This was an important revelation in the 1930sand was responsible for much of the early growth in the adoption of CA storage technol-ogy (Dilley, 2006). Robert Smock joined Allen in California and extended the CA storageinvestigations on apples and broadened the studies with peaches, pears, and plums (Allenand Smock, 1937),and continued his investigations upon moving to Cornell University inthe late 1930s.Nearly 20 years would pass before CA storage of apples was an acceptedtechnology in the Pacific Northwest and Archie Van Doren was largely responsible for itscommercialization (Dilley, 2006). The commercial development of CA storage of applesand pears in Canada can be largely attributed to the research of Charles Eaves of theCanada Department of Agriculture, and Agriculture Canada Research Station at Kentville,Nova Scotia, where he made numerous significant and innovative contributions (Eaves,1959,1960, 1963).

MA and CA research have extended later in different regions and included differentcommodities. CA studies on citrus were conducted in Florida and California and oncranberries in Massachusetts. The first commercial CA storages in Elgin, South Africa wasestablished in 1935 and 1936, but only operated successfully for a short period of timebefore being converted into conventional refrigerated air storage (Dilley, 2006). The firstcommercial CA storage in modem times in the Western Hemisphere was established inNova Scotia, Canada in 1939, followed in 1940 by equipping existing refrigerated fruitstorage rooms for operation as CA storages at Lockport and at Sodus, New York,followed by construction of new CA storage enterprises in the Hudson Valley in NewYork State (Dilley, 2006). Gradual expansion of CA storage capacity continued inNew York and eastern Canada during the 1940s, and in New England in the 1950s,where CA storage was used largely for Mdntosh, the major dessert apple variety in theseregions (Dilley, 2006). An active period of expansion in CA storage in the United Statesand Canada began in the 1950s,and the most significant and accelerated expansion beganin the 1960s when Washington state apple storage operators and shippers realized theimprovements to be gained in dessert quality and marketability of Red and GoldenDelicious apples by storing them under CA (Dilley, 2006). By 1960, the total CA holdingsof apples and pears in the United States amounted to over 4 million bushels, and by thelate 1980s,CA storage capacity for apples and pears exceeded 100 million bushels (Dilley,2006).CA storage rooms have been established in several countries in all the continentssuch as several European countries, South Africa, Egypt, Jordan, India, Mexico (since1980),Chile, Argentina, among others. MA for transport was used already in the 1930s,when ships transporting fruits had high levels of caz in their holding rooms, thusincreasing the shelf life of the producto In Mexico, trials of using MA during marineshipping of mango started in 1974.

...lntroduction 5

6 Modified and Controlled Atmospheres lntroduction

1.3 Gases Used

MA and CA usual1y consist of Nz, O2, and caz. It is the altered ratio of Oz and caz thatmakes a difference in the preservation of food commodities. By reducing the Ozlevel andincreasing the caz level, ripening of fruits and vegetables can be delayed, respiration andethylene production rates can be reduced, softening can be retarded, and various compos-itional changes associated with ripening can be slowed down. Oxygen is essential for therespiration of fresh horticultural commodities. The removed Oz can be replaced with Nz,commonly acknowledged as an inert gas, or caz, which is a competitive inhibitor ofethylene action and can lower the pH or inhibit the growth of some fungi and bacteria.Respiration rate starts to decrease when O2 level is decreased to below 12 kPa, and levelscommonly used for most fresh horticultural commodities is about 3-5 kPa. The absence ofOz can lead to anaerobic respiration, accelerating deterioration, and spoilage. High cazlevels are effective bacterial and fungal growth inhibitors; however, levels ~10 kPa areneeded to suppress fungal and bacterial growth significantly. Atmospheres >10 kPa cazcan be phytotoxic to many fresh horticultural commodities. Nitrogen is used as a filler gassince it has no direct biological effects on horticultural commodities, and therefore Nz iscommonly used as the inert component of MAjCA. Replacing Nz with argon or heliummay increase diffusivity of 0z, COz, and CZH4' but they have no direct effect on planttissues and are more expensive than Nz as an MAjCA component.

1.4 Biological Basis of MAleA Effects

There are basic biologically defined limits to the environment that can be employed for thepostharvest preservation of fresh horticultural commodities. Basic biological processes inthese commodities such as transpiration, respiration, and biochemical transformationscontinue after harvest. However, these processes can be altered by manipulating differentfactors such as temperature, RH, and the concentration of biological1y active gases suchas water vapor, 0z, caz, and ethylene, among others. Beyond certain limits of thesefactors, especially gas atmosphere composition, and according to stage of developmentof the commodity, physiological disorders may develop, which can termínate the usefullife of the commodity by negatively affecting appearance, flavor, nutritive value, orwholesomeness.

Optimum ranges of Oz and caz levels can result in several advantages to the foodcommodity, but unfavorable atmospheres can induce physiological disorders and enhancesusceptibility to decay, among other possible problems. Elevated COz-induced stresses areadditive to and sometimes synergistic with stresses caused by low Oz; physical or chemicalinjuries; and exposure to temperatures, RH, andjor CZH4 concentrations outside theoptimum range for the commodity. The shift from aerobic to anaerobic respiration dueto low Oz andjor high caz atmospheres depends on fruit maturity and ripeness stage (gasdiffusion characteristics), temperature, and duration of exposure to stress-inducing condi-tions. Up to a certain limit, fresh horticultural commodities are able to recover from thedetrimental effects of low Oz andjor high caz stresses and resume normal respiratorymetabolism upon transfer to normal air. Plant tissues have the capacity for recovery fromthe stresses caused by extreme gas atmospheres, and postclimacteric tissues are lesstolerant and have lower capacity for recovery than preclimacteric fruits. The speed andextent of recovery from reduced Oz and elevated caz stress depend upon gas level,physiological stage of the tissue, temperature, and duration of exposure.

Elevated c(ethylene biosyat high CO2 é

spheres. OptiJsynthesis of Cé

colors), and b:CA slow dOWland enzymesandjor high lsugar conversChapter 7) (Yiand other vitacaz stress, es}levels, and rechol dehydrogE1995). This calwhich may blconditions beyatmospheres vatures and diexample, man¡avocado and ~

MAjCAcanon decay incisignificantIy itperishables. Hing and tissuetool for insectand grains, anChapter 11).

Superatmos}degreening ofand ethylenepon apples and 1

postharvest pain MAjCAwilfungistatic, ele1Chapter 9).

Developmenhorticultural C(

aspects ofbiol{distribution of

1.5 PotentiaSome detrimenlevels higher tintensities of thsuch as temper

1.5 Potential Detrimental Effects

Somedetrimental effects can result, especially due to the use of Ozlevels lower andjor cazlevels higher than the ideal for each commodity (see Chapter 8). The incidence andintensities of these potential detrimental effects can be influenced by several other factorssuch as temperature, RH, other gases such as ethylene, type of product, cultivar, stage of

Elevated caz atmospheres inhibit activity of ACC synthase, a key regulatory site ofethylene biosynthesis, while ACC oxidase activity is stimulated at low caz and inhibitedat high caz andjor low Oz levels. Ethylene action is inhibited by elevated caz atmo-spheres. Optimum atmospheric compositions retard chIorophyll loss (green color), bio-synthesis oí carotenoids (yellow, orange, and red colors) and anthocyanins (red and bluecolors), and biosynthesis and oxidation of phenolic compounds (brown color). MA andCA slow down the activity of the cell wall, degrading the enzymes involved in softeningand enzymes involved in lignification, leading to toughening of vegetables. Low O2andjor high caz atmospheres influence flavor by reducing loss of acidity, starch tosugar conversion, sugar interconversions, and biosynthesis of aromatic volatiles (seeChapter 7) (Yahia, 1994). Optimum atmospheres can help the retention of ascorbic acidand other vitamins, resulting in better nutritional quality (see Chapter 6). Severe Oz andCOzstress, especially very high caz atmospheres, can decrease cytoplasmic pH and ATPlevels, and reduce pyruvate dehydrogenase activity while pyruvate decarboxylase, alco-hol dehydrogenase, and lactate dehydrogenase are induced or activated (Ke et al., 1994,1995).This causes accumulation of acetaldehyde, ethanol, ethyl acetate, andjor lactate,which may be detrimental to the commodities if they are exposed to stress MAjCAconditions beyond their tolerance (see Chapter 11). However, relative tolerance to severeatmospheres varies among different products, cultivars, ripening stages, storage temper-atures and duration of exposure, and in some cases, ethylene concentrations. Forexample, mango fruit is much more tolerant to extreme atmospheric stress compared toavocado and guava (Yahia, 1998a,b).

MAjCA can have a direct or indirect effect on postharvest pathogens and consequentIyon decay incidence and severity (see Chapter 9). For example, caz at 10-15 kPasignificantly inhibits development of Botrytis rot on strawberries, cherries, and otherperishables. However, other atmospheres may reduce decay by indirectly delaying ripen-ing and tissue softening. Low Oz (:::;1kPa) andjor elevated caz (2=:50kPa) can be a usefultool for insect control in some fresh and dried fruits, flowers, vegetables, and dried nutsand grains, and this effect is more evident at higher temperatures (Yahia, 1998a,b; seeChapter 11).

Superatmospheric levels of Oz of up to about 80 kPa may accelerate ethylene-induceddegreening of nonclimacteric commodities and ripening of climacteric fruits, respiration,and ethylene production rates, and incidence of some physiological disorders such as scaldon apples and russet spotting on lettuce. At levels above 80 kPa 0z, some commodities andpostharvest pathogens can suffer from Oz toxicity. The use of superatmospheric Oz levelsin MAjCA willlikely be limited to situations in which they reduce the negative effects offungistatic, elevated caz atmospheres on commodities that are sensitive to caz injury (seeChapter 9).

Development and application oí successful postharvest preservation techniques for freshhorticultural commodities depends largely on the understanding of certain fundamentalaspects of biology, engineering, and economics that are important in the maintenance anddistribution of these perishables.

7lntroduction

8 Modified and Controlled Atmospheres

ld . .1

lntro uction

MA and CA!apples, avpeaches, pedetails). Trfruits and VIencourage .transport cregimes wheone or morestrict controlall transportdevelopedthough usufor transportilhindered itssystems forsystems andand benefitssystems weunsuccessful.to deteriora"

tolerance levlcultivars, thefruits espedfruit can becarried out.(hypobaricreducedpredependingshelf life ofBurg, 1975;Yahia, 1997b1977b;Spal1997d),papaused for ameats, flowe:traditionaladministerediin an adequYahia, 1997arCA storageof optimal 1,CA, low estorage, forOz for therlby separati,improved ti

1.6.1 StorageCA storage is not universally adaptable to all crops. It is a technology where freshperishable commodities are stored under narrowly defined environmental conditions toextend their postharvest life (see Chapter 2 for more details). The ideal levels of theseenvironmental variables differ according to commodity and stage of development. More-over, tissue response may vary because of interactions among these variables as influencedby variety and preharvest conditions and climatic factors. Commercial use of CA storage iscommon for apples and pears, less common for cabbages, sweet onions, kiwifruits, avo-cados, persirnmons, pomegranates, nuts and dried fruits, and vegetables. Applications ofCA to ornamentals and cut flowers (see Chapter 19)are very limited because decay causedby Botrytis cinerea is often a limiting factor to postharvest life, and fungistatic caz levelsdamage flower petals andjor associated stem and leaves. Also, it is less expensive to treatflowers with antiethylene chemicals than to use CA to minimize ethylene action. CAstorage technology does not seem to be as promising for many tropical fruits (Yahia,1998a;Yahia and Paull, 1997;see Chapter 16) when compared to temperate fruits. This isdue to several reasons including those related to crop availability and quantity, preharvestand postharvest handling, and availability of technology. Except for bananas, tropicalcrops carmot be stored for prolonged periods that would justify the use of CA. Manyfactors should be considered when evaluating the potential application of MAjCA such asfruit quantity and value, reason for the use of MAjCA (control of metabolism, control ofpathogens, control of insects, etc.), availability of alternative treatments, competition withother production regions, type of market (local, distant, export, etc.), and type of prehar-vest and postharvest technology available in the region. Apple, a fruit very compatible tothe use of CA (see Chapter 12), is a high value fruit, produced in large quantities, andcharacterized by a climacteric respiration and a long postharvest life. In addition, theproduction and action of ethylene is controlled by CA, a large variation exists in the

1.6 Technological ApplicationsThe most important applications of MA and CA for fresh horticultural commodities arestorage, long distance marine transport, and packaging.

development of the commodity, storage duration, among others. Some of the detrimentaleffects can be shown as initiation andj or aggravation of certain physiological disorderssuch as internal browning in apples and pears, brown stain of lettuce, and chilling injury ofsome commodities. Irregular ripening of some fruits, such as banana, mango, pear, andtomato, can result from exposure to Ozlevels below 2 kPa andjor COzlevels above 5 kPafor more than 1 month. Development of off-flavors and off-odors can occur at very low Ozlevels and/or very high caz levels as a result of anaerobic respiration and fermentativemetabolismo Susceptibility to decay can increase due to exposure to very low Oz andjorvery high caz atmospheres. Therefore, inadequate atmospheres can cause the aggravationor the initiation of physiological disorders (see Chapter 8), and can increase the hazard ofmicrobial contamination of minimally processed products (Chapter 10). MA and CA canbe deadly to humans getting inside a room or a container without proper security equip-ments or before the room or the container is properly ventilated (see Chapters 2 and 3). MAand CA can cause structural damage to rooms and containers that lack proper pressurerelief systems, or due to inadequate use of some gases such as propane.

1.6.2 Transport

MA and CA for long-distance marine transport is used on many commodities, such asapples, avocados, bananas, blueberries, cherries, figs, kiwifruits, mangoes, nectarines,peaches, pears, plums, raspberries, melons, and strawberries (see Chapter 3 for moredetails).Transport of meat in MA has started since about seven decades ago, and that offruits and vegetables since about three to four decades ago. The use of MAjCA canencourage the use of sea transport, since it is cheaper than air transporto Atmospheres fortransport can be developed passively, semiactively, or actively. Passive systems are MAregimeswhere the atmosphere is modified by fruit respiration. In the semiactive systems,one or more gases isjare added or withdrawn, most commonly at the beginning, but nostrictcontrol is carried out. Active systems imply a strict control of the atmosphere duringalltransport periodoThe most common systems for transport in the last 30 years have beendeveloped on a semiactive basis, and used for transport of bananas and strawberries,though usually less efficient, they are less expensive than active systems. The use of CAfor transport has been contemplated for several decades; however, several problems havehindered its success, including the unavailability of adequate gastight containers, suitablesystems for gas control and analysis, and adequate CA-generating systems. Existingsystemsand companies before the 1980swere unable to deliver on promised applicationsandbenefits of MAjCA transport systems. Liquid Nz and pressure swing adsorption (PSA)systems were tried first to create and maintain CA systems in sea containers but wereunsuccessful.The disadvantage of the PSA systems is the susceptibility of the carbon sieveto deterioration in high-vibration environments. Liquid Nz has high boil-off rate and can

tolerancelevels for Oz and caz, CA permits the use of lower storage temperatures in somecultivars, the fruit is relatively less infected by pathogens and insects compared to otherfruits especially of tropical origin, some physiological disorders can be alleviated by CA,fruit can be harvested and stored in bulk, and a great deal of MAjCA research has beencarried out. No tropical fruit, except banana, meets these qualifications. Low pressure(hypobaric or LP storage) refers to holding the commodity in an atmosphere under areduced pressure, generally, <200 mmHg. In this system, the Oz concentration is reduceddepending on the atmospheric pressure. LP has been reported to extend the storage andshelf life of several crops (Gemma et al., 1989) including mangoes (Burg and Burg, 1966;Burg,1975;Spalding, 1977a;Spalding and Reeder, 1977;Ilangantileke and Salokhe, 1989;Yahia,1997b),avocados (Burg and Burg, 1966;Spalding and Reeder, 1976;Apelbaum et al.,1977b;Spalding, 1977a), bananas (Burg and Burg, 1966; Apelbaum et al., 1977a; Yahia,1997d),papayas (Alvarez, 1980;Yahia, 1997c),and cherimoyas (Plata et al., 1987).LP wasused for a short period in the 1970s during transport of some food products includingmeats, flowers, and fruits (Byers, 1977).However, this system is more expensive than thetraditional MAjCA systems. Furthermore, some fruits require other gases that carmot beadministered during low-pressure storage. For example, caz is an important componentin an adequate atmosphere for avocado (Spalding and Reeder, 1976; Spalding, 1977a;Yahia,1997a).CurrentIy, this system is not used commercially. Several developments inCA storage have been made in recent years including rapid CA (rapid establishmentof optimal levels of Oz and Caz), ultra low Oz (1.0-1.5 kPa) CA storage, high cazCA, low ethylene (:<:;1µL L-l) CA storage, and programmed (or sequential) CAstorage, for example, storage in 1 kPa Oz for 2-6 weeks followed by storage in 2-3 kPaO2 for the remainder of the storage periodoOther developments included creating nitrogenby separation from compressed air using molecular sieve beds or membrane systems,improved technologies of establishing, monitoring, and maintaining CA.

lntroduction 9

10 Modified and Controlled Atmospheres lntroduction

run out in the middle of the ocean, making it difficult to refill, and thus the CA wouldbe lost. In the late 1980s, the concept of CA transport became more practical due to theavailability of gastight containers, adequate gas control systems, and the ability to establishand maintain controlled gas mixes. The use of air separation technologies in the 1980s,especially the introduction of membrane technology in 1987,made CA transport practicaland feasible. The use of CA for food transport commodities is now a practical reality,although several systems are still misleadingly called CA when they are in reality MAsystems with no capacity to control most of the gases. A CA container has the samefeatures as that of a refrigerated container, in addition to a higher level of gastightness,Oz and caz control systems, and perhaps systems for control of ethylene and RH. CAsystems for transport should be used when transport periods are long andjor food is veryperishable. The "Oxytrol system," which was the first commercially available MA system,was developed by Occidental Petroleum Corporation, California. It is a self-containedsystem designed to be used as an adjunct in refrigerated transport vehicles. The maincomponents of the system are an oxygen sensor, electronic analyzer-controller, liquidnitrogen storage tank, liquid nitrogen vaporizer, gas discharge nozzle, and peripheralequipment. The liquid nitrogen tank can be filled before, during, or after loading. UquidNz is vaporized and warmed prior to injection into the transport vehicle. caz is controlledusing hydrated lime. This system has been used for highway and sea shipments of lettuce,celery, papaya, and pineapple. "Tectrol" (total environment control) was developed andfirst used by Transfresh Corporation, California, in 1969.For transport, tight refrigeratedtransport units (railroad, highway, or sea) are flushed with the desired premixed gas blendand then sealed. The "Tectrol" unit consists of nitrogen tanks, which are controlled tocorrect for the deviation of oxygen. This system was only satisfactory when oxygen was theonly gas to be controlled, and the trip was short. Ume and magnesium sulfate are used tolower the concentrations of caz and CzH4' respectively. Some of the crops transported inthis system include lettuce, strawberry, mango, and avocado. Newer Tectrol systemsincluded a controller that monitors, controls, and records Oz and caz· An interface systemallows the controller to manage the container environment without external interference.The "CONAIR-PLUS" system (G +H Montage GmbH, Hamburg, Germany) can create aCA system through the introduction of Nz (generated under pressure) by means of amembrane from the ambient air to the container. This system can also control caz andethylene, and has been used to transport apple, avocado, melon, and mango. The maritimeprotection division of Permea, Inc. (St. Louis, Missouri) developed the first membrane-based CA system (PRISMCA) in 1987.This system contains gas analyzers and computermicroprocessors for establishing and maintaining the CA system. It was designed to beinstalled on the weather deck of a refrigerated ship, and to establish, monitor, and controlCA conditions. After completion of the voyage, the system can be flown back to the port oforigin in the cargo hold of a 747aircraft (it is designed to occupy the same space as an LD-29 aircraft cargo container). The system was first used by the New Zealand Apple and PearBoard, then by Cool Carriers to transport apples, and lately was used in some otherships. Other systems have been developed in the last few years such as Freshtainer(Maidstone, England) and NITEC (Spokane, Washington), among others (see Chapter 3).Important developments in the transport of foods in MAjCA have been accomplishedin the last years, among them are the development of better sealed containers, air separ-ation techniques, better gas monitoring and control systems. However, major problemsare still facing the industry to select the adequate MAjCA transport system. MAjCAtransport companies need to work much more closely with the industry. They need toinvestigate in more detail the ideal conditions of each specific MAjCA system for eachcommodity, especially in relation to stage of maturity, cultivar differences, distances oftransport, etc.

1.6.3 Packaging

Modified atmosphere packing (MAP), a technique used to prolong the shelf life of fresh orminimally processed foods, refers to the development of an MA around the productthrough the use of permeable polymeric filrns. MAP is used with various types of products,where the mixture of gases in the package depends on the type of product; packagingmaterials and storage temperature (see Chapters 4, 5, and 18 for more details). Freshhorticultural commodities are respiring products where the interaction of the packagingmaterial with the product is important. If the permeability (for Oz and Caz) of thepackaging film is adapted to the products, respiration, an equilibrium MA will be estab-lished in the package and the shelf life of the product can be improved (Yahia andGonzalez, 1998; Yahia and Rivera-Dominguez, 1992). In reality, the concept of MAP isnot new with early research being reported in the late 1800s.The use of MAs for shelf lifeextension was conceived as a new food preservation method with the discovery of thepreservative action of carbon dioxide over a century ago. In the 1970s, MA packagesreached the stores when bacon and fish were sold in retail packs in the United Kingdom.Sincethen the development has been stable and the interest into MAP has grown due toconsumer demando This has led to many advances, such as in the design and manufactur-ing of polymeric films. New techniques are designed, like the use of antifogging layer toimprove product visibility. Equilibrium-modified atmosphere packaging (EMAP) is acommonlyused packaging technology for fresh-cut produce.

MAP is a technique that has gained tremendous popularity in the last years. It can bebroadly defined as any process that significantIy changes the environment around theproduct from the normal composition of air in a package. The generic term also includesapplications such as vacuum packaging. MAP can be used in combination with a numberof other food processing, preservation systems, and packaging techniques to maintainproduct quality and extend shelf life. MAP benefits to the food product are extendedshelflife and maintenance of flavor, taste, texture, color, and nutritive value. Nonetheless,MAP, as it is the case in MA and CA, carmot arrest all degradation processes such asstaling,or improve abad producto Packaging carmot be held solely responsible for uphold-ing the quality and shelf life of MAP products.

Selectionof a MAP system depends on a variety of factors, including shelf life, distri-bution requirements, importance of bloom, product dimensions, and marketing objective.The selection of gas mixtures used in a MAP system is influenced by the microbiologicalfloraon the food product, caz and Oz sensitivity of the product, and pigment stabilizationrequirements, among other factors. Although many gas formulations have been investi-gated to optimize the MAP process, the main gases remain to be Oz, Nz, and caz, whichcanbe used separately or mixed together. The best results are obtained when gas mixturesand processes are tailored to specific applications.

Thegrowth in MAP fresh-cut (minimally processed) produce is one of the most dynamicin the last decade. Produce packaging involves a delicate balance of the product's respir-ation rate, product temperature, and the permeability of packaging material. The selectionof the correct packaging material is crucial to maintain the desired balance of Oz and cazwhich, in turn, slows the product's metabolism, and thus product senescence.

Although gas atmosphere is important, other criteria must be considered when contem-plating MAP technology, which include temperature and RH control, packaging equip-ment, packaging materials, and food safety issues. High-performance packaging andpackaging equipment are continually evolving. Technological advancements in packagingmachinery have focused on higher speeds, lower residual oxygen levels, and washdownsanitation construction. High-performance filrns can be defined as films that truly meet thecustomer's expectations in various roles as both the communicator and a protector.

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12 Modified and Controlled Atmospheres lntroduction ;

Packaging is increasingly important as part of the communicator role to reach theconsumer through printing and package appearance. In addition, new packaging tech-nologies are creating advancements in barrier polymers, improved sealant polymers, andabuse properties.

Emerging packaging technologies are continually evolving to prolong the quality offresh, refrigerated, and minimally processed foods. These emerging technologies includeactive packaging including oxygen-scavenging films, high oxygen barrier polymers andhigh oxygen permeable fi1ms, and polymers with refined properties. Active packaginginvolves technologies in which the package interacts with the internal package atmosphereandjor the food in the package. The active system can be an integral part of the package orbe a separate component placed inside the package. Substances that can either absorb(scavenge) or release (emit) a specific gas can control the internal atmosphere of thepackage. Commercial examples of "scavenger" and "emitter" technologies include oxygenscavengers to create low Oz environment and slow metabolism; ethylene scavengers toslow senescence of produce; caz scavengers to remove caz from coffee; caz emitters toretard microbial growth; and ediblejbiodegradable barriers to moisture andjor Oz· Otheractive systems slowly release the active substances onto the food surface including anti-microbial agents, antioxidants, color transfer fi1ms; flavor j odor absorbers or releasers,enzyme inhibitors, and moisture scavengers.

Some important MAP developments include, among others, creating nitrogen by separ-ation from compressed air using molecular sieve beds or membrane systems, improvedtechnologies of establishing, monitoring, and maintaining the atmosphere, using of ediblecoatings or polymeric films with appropriate gas permeability to create a desired atmos-pheric composition around and within the commodity.

Some of the disadvantages of MAP include added cost, capital cost of packaging, andquality control machinery; added cost of gases and high barrier films, and added transportcost and display space due to increased pack volume. However, the rapid growth of MAPproducts in the marketplace indicates that the benefits of the system to the retailer,manufacturer, and consumer clearIy outweigh the disadvantages.

Food safety must continue to be of prime concern of MAP food. Good manufacturingpractices along with the implementation of a hazard analysis of critical control points(HACCP) system are the ideal way to ensure a safe producto In addition, hurdle technologywill be imperative to the success of refrigerated, minimal1y processed foods. The effectiveand safe use of MAP requires effective control of temperature. Poor temperature controleliminates the beneficial effects of any MAP system and may cause health hazards.

1.7 Some Additional TreatmentsThe use of carbon monoxide in addition to MA and CA can provide several advantagessuch as the control of pathogenic diseases and insects (Woodruff, 1977; El-Goorani andSommer, 1981), and tissue browning and discoloration (Kader, 1986). However, the devel-opment of safe methods of application such as the addition of odors is required before anycommercial use can be considered (Yahia et al., 1983). The use of CO has to be combinedwith low (::;4kPa) Oz atmospheres (Kader, 1986). CO can increase the production of Cz~;however, at high concentrations this did not appear to happen (Woodruff, 1977). Ithas been reported that for fruits that tolerate elevated caz, CO appear to be more effective.Ethylene removal during transport and storage in CA can be beneficial in delayingripening. Atmospheres with very low Oz content (::;1.0kPa) andjor very high caz levels(2:50kPa) have insecticidal effects (Yahia, 2006). Insect control with MA and CA depends

on theOzandand duration!tration, the hijthe time necdadvantages ~.'ments that dichemical ~compared toicompared to 1for short perilat high tem~tolerate these1atmosphereslCarrillo-LOMtemperaturesj

1.8 Some'Most chapteqtopics. Some~need to bette~of fresh who.continUing~.:log~caldisor ,a glven co ,needed to el .monoxide on jextreme atmojstill needs forJities includin8their effectiv~Investigationl

especially in i·•...·.'fruit quality. •to determineeach type of

;1

~1.9 ConclqMAandCA~be used dadvanceshaofuse ofthediverse regi'order to incespecially th,transport.

1.9 Conc1usions

1.8 Some Future Research Needs

MAand CA are important technologies for the preservation of food commodities. They canbe used during storage, transport, and packaging. Major research and developmentsadvances have been accomplished in the last few decades, which allowed for the diversityof use of the technology (for more food products, for different types of applications, and indiverse regions in the world). However, major R&D is still needed in all applications inorder to increase the use of the technology for more commodities and applications, butespecially there is much more need for more research and development on MAjCAtransport.

13

Most chapters in this book contain suggestions for future research needs of each of thetopics. Some of the general research needs are specified here. There is a continuing researchneed to better understand the biological bases of Oz and caz effects on postharvest qualityof fresh whole and fresh-cut horticultural commodities. There is still a strong need forcontinuing investigations of the physiological and biochemical basis of CA-induced physio-logical disorders, and to determine the reasons behind genotypic differences in tolerance ofa given commodity to reduced Oz andjor elevated caz concentrations. Research is stillneeded to elucidate the mode of action of elevated Oz, elevated caz, ethylene, and carbonmonoxide on postharvest pathogens and insects. Bases for wide variability in tolerance toextreme atmospheres among different commodities still need to be understood. There arestillneeds for continued development of optimum MAP technologies for various commod-itíes including evaluation of various types of oz, caz, CZH4' and water vapor absorbers fortheir effectiveness in helping to maintain the desired microenvironment within MAP.Investigation is needed to determine the potential of using superatmospheric Oz levels,especially in addition to high levels of caz for decay control without detrimental effects onfruit quality. Significant research is still needed, especially by MAjCA transport companies,to determine the optimum use of the diverse systems used, the optimum conditions witheach type of product, cultivar, stage of maturity, duration of shipping trip, etc.

on the Oz and caz concentration, temperature, RH, insect species and development stage,and duration of the treatment (Yahia, 1997e; Yahia et al., 1997). The lower the Oz concen-tration, the higher the caz, the higher the temperature, and the lower the RH, the shorterthe time necessary for insect control (Yahia, 1998a,b, 2006). MA and CA have severaladvantages in comparison with other means for insect control. These are physical treat-ments that do not leave toxic residues on the fruit, and are competitive in costs withchemical fumigants. MA and CA do not accelerate fruit ripening and senescence ascompared to the use of high temperatures, and have better consumer acceptance ascompared to the use of irradiation. In order to establish quarantine insect treatmentsfor short periods of times, extreme gas atmospheres (:::;0.5kPa Oz andjor 2':50kPa Caz)at high temperatures (2':20°C) should be implemented (Yahia, 2006). Some fruits do nottolerate these treatments. For example, 'Hass' avocados are injured when exposed to theseatmospheres for more than 1 day at 20°C (Carrillo-Lopez and Yahia, 1990; Yahia andCarrillo-Lopez, 1993; Ke et al., 1995). The application of insecticidal atmospheres at hightemperatures can accelerate the mortality of insects (Yahia, 2006).

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14 Modified and Controlled Atmospheres lntroduction

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subatmospheric pressure. HortScience 12:115-117.Biale, J. 1942. Preliminary studies on modified air storage of Fuerte avocado fruit. Proceedings of the

American Society Horticultural Science 41:113-118.Bigelow, W.D., H.e Gore, and B.J. Howard. 1905. Studies on apples. United States Department

Agriculture Bureau Chemical Bulletin 94:9-10.Brooks, e, J.e eooley, and D.F. Fisher. 1919. Nature and control of apple scald. ¡oumal of Agricultural

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Wallingford, U.K., 654 pp.Burg, S.P. and E.A Burg. 1965. Ethylene action and the ripening of fruits. Science 148:1190-1196.Burg, S.P. and E.A Burg. 1966. Fruit storage at subatmospheric pressures. Science 153:314-315.Byers, B. 1977. The Grumman Dormavac system. In: Dewey, D.H. (Ed.), Controlled Atmospheres for

the Storage and Transport of Perishable Agricultural Commodities. Proceedings of the 2nd NationalCA Research Conference Horticulture Report 28. Department of Horticulture, Michigan StateUniversity, East Lansing, MI, pp. 82-85.

earrillo-Lopez, A and E.M. Yahia. 1990. Tolerancia del aguacate varo Hass a niveles insecticidas deO

2y eoz y el efecto sobre la respiración anaeróbica. Tecnología de Alimentos (México) 25(6):13-18.

Dalrymple, G.D. 1969. The development of an agricultural technology: eontrolled atmospherestorage of fruits. Technology Culture 10(1):35-48.

Dilley, D.R 1990.Historical aspects and perspectives of controlled atmosphere storage. In: Caldron, M.and Barki-Golan, R (Eds.), Food Preservation by Modified Atmospheres. eRe Press, Boca Raton, FL,pp. 187-196.

Dilley, D.R 2006. Development of controlled atmosphere storage technologies. Stewart PostharvestReview 20066:5. www.stewartpostharvest.com

Eaves, eA 1959. A dry scrubber for CA apple storages. Transactions of the American Society Agricul-tural Engineers 2(1):127-128.

Eaves, eA 1960. A Plastic storage for apples with semi-automatic controlled atmospheres. CanadianRefrigeration Air Conditioning 26(12):29-33.

Eaves, eA 1963. Atmosphere generators for CA apple storages. Annual Report Nova Scotia FruitGrowers Association 1963 100:107-109.

El-Goorani, M.A and N.F. Sommer. 1981. Effects of modified atmospheres on postharvest pathogensof fruits and vegetables. Horticulture Review 3:412-461.

Fidler, J.c., B.L. Wilkinson, K.L. Edney, and RO. Sharples. 1973. The Biology of Apple and Pear Storage.Research Review 3, eommonwealth Agriculture Bureau, England, pp. 235.

Frenkel, e, I. Klein, and D.R Dilley. 1968. Protein synthesis in relation to ripening of pome fruits.Plant Physiology 43:1146-1153.

Gemma, H., e Oogaki, M. Fukushima, T. Yamada, and Y. Nose. 1989. Preservation of some tropicalfruits with an apparatus of low pressure storage. ¡oumal of ¡apanese Society of Food Science andTechnology 36:508-518.

Hill, G.R 1913. Respiration of fruits and growing plant tissues in certain gases, with reference toventilation and fruit storage. Comell University of Agricultural Experimental Station Bulletin330:377-408.

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Ilangantileke, ~Storage R114-16, 1~

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Ke, D., E. Y~avocadotcultural 54

Ke, D., E. y~influenc~Horticul~

Kidd, F. and qIndustrid

Kidd, F. and qResearchl

Kidd, F. and q¡oumal of~

Kidd, F. and qethylene 1Great Bri~pp. 101-~

Kidd, F. and elIndustria]

Overholser, E.IjPlata, M.e, L.d

protein ~ripeningijAliment. i

Spalding, D.H.1D.H. (Ed.~ties. Har~

Thatcher, R.W.:Agricultu~

Woodruff, R.E.!transito miAgricultu1Departm~

Yahia, E.M. 1~Yahia, E.M. 199

AA (Ed;lCalifornia)

Yahia, E.M. 19~Apples a~

Yahia, E.M. 1~Apples ami

Yahia, E.M. 1991thanAppl1!l

Yahia, E.M. 1~ThompsoI1CA'97 Proj

Yahia, E.M. 1~22:123-183

Hulme, Ae., M.J.e. Rhodes, T. Gaillard and L.S.e. Wooltorton. 1968. Metabolic changes in excisedfruit tissue. IV. Changes occurring in discs of apple peel during the development of therespiration climacteric. Plant Physiology 43:1154-1161.

Ilangantileke,S. and V. Salocke. 1989.Low-pressure storage of Thai mango. In: Other Commodities andStorage Reconditions, Vol. 2. Proceedings of the Fifth CA Research Conference Wenatchee, WA, June14-16,1989, pp. 103-117.

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Ke, D., E. Yahia, M. Mateos, and A Kader. 1994. Ethanolic fermentation of 'Bartlett' pears asinfluenced by ripening stage and controlled atmosphere storage. Journal of American Society forHorticultural Sciences 119(5):976-982.

Kidd,F. and e. West. 1927a.Atmosphere control in fruit storage. Great Britain Department ScientificIndustrial Research Food Investigation Board Report, 1927,pp. 32-33.

Kidd, F. and e. West. 1927b. Gas storage of fruit. Great Britain Department Scientific IndustrialResearch Report 30, pp. 87.

Kidd, F. and e. West. 1930. The gas storage of fruit. n. Optimum temperatures and atmospheres.Journal of Pomology and Horticultural Science 8:67-77.

Kidd,F. and e. West. 1937.Action of carbon dioxide on the respiration activity of apples. Effect ofethylene on the respiration activity and climacteric of apples. Individual variation in apples.Great Britain Department Scientific Industrial Research Food Investigation Board Report, 1937,pp. 101-115.

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protein content and polyphenoloxidase and peroxidase activities in chirimoya induced byripening in hypobaric atmospheres or in presence of sulfite (in Spausi)., Rev. Ageoquim Temol.Aliment. 27: 215-224.

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16 Modified and Controlled Atmospheres

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(eA) uses with tropical fruits. Chronica Horticulturae 37(4):18-19.Yahia, E.M., K.E. Nelson, and A.A. Kader. 1983. Postharvest quality and storage life of grapes as

influenced by adding carbon monoxide to air or controlled atmospheres. Journal of the AmericanSociety of Horticultural Science 108(6):1067-1071.

Yahia, E.M. and M. Rivera-Dominguez. 1992. Modified atmosphere packaging of muskmelon. FoodScience and Technology (Lebensmittel Wissenschaft und Technologie) 25:38-42.

Yahia, E.M., D. Ortega, P. Santiago, and L. Lagunez. 1997. Responses of mango and mortality ofAnastrepha ludens and A. obliqua to modified atmospheres at high temperatures. In: Thompson,J.F. and Mitcham, E.J. (Eds.), CA Technology and Disinfestation Studies, Vol. 1. CA'97 Proceedings.University of ealifomia, Davis, CA, pp. 105-112.

2Storage

CONTENTSj'!

2.1 Introdu2.2 CAM

2.2.12.2.22.2.32.2.42.2.52.2.62.2.72.2.82.2.92.2.10

2.3 Storage2.3.12.3.22.3.32.3.42.3.5

2.4 Establ'2.4.12.4.22.4.3

2.5 Control2.5.12.5.22.5.32.5.42.5.5

2.6 Safety e2.7 FutureReferences ....