Introduction

CONTENTS 1.1 Introduction ............................................................................................................................ 1 1.2 History..................................................................................................................................... 3 1.3 Gases Used.............................................................................................................................. 6 1.4 Biological Basis of MA=CA Effects ..................................................................................... 6 1.5 Potential Detrimental Effects................................................................................................ 7 1.6 Technological Applications .................................................................................................. 8

1.6.1 Storage .......................................................................................................................... 8 1.6.2 Transport ...................................................................................................................... 9 1.6.3 Packaging ................................................................................................................... 11

1.7 Some Additional Treatments ............................................................................................. 12 1.8 Some Future Research Needs ............................................................................................ 13 1.9 Conclusions........................................................................................................................... 13 References...................................................................................................................................... 14

Modified atmosphere (MA) refers to any atmosphere different from the normal air (20%–21% O2, about 0.03% CO2, about 78%–79% N2, and trace quantities of other gases), while controlled atmosphere (CA) refers to atmospheres different than normal air and strictly controlled during all time. MA and CA usually involve atmospheres with reduced O2 and=or elevated CO2 levels. Hypobaric (low pressure) storage is a CA system involving the use of vacuum to reduce the partial pressure of the gas component of air (Burg, 2004; Yahia, 2004). The technologies 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 ripening and senescence of horticultural commodities, control of some biological processes such as rancidity, insects, bacteria and decay, among others. MA and CA combined with precision temperature management allow nonchemical insect control in some commodities for markets that have restrictions against pests endemic to exporting countries and for markets that prefer organic produce (see Chapter 11). Major developments have been accomplished in the last two to three decades, such

as better construction of sealed storage rooms (see Chapter 2) and transport containers (see Chapter 3), better gas monitoring and control systems, and new packaging systems (see Chapters 4 and 5). Optimum atmosphere for different types of foods is very variable,

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 of different types of foods (especially horticultural products) to O2 levels below, and=or CO2 levels above their optimum tolerable range can cause the initiation and=or aggravation of certain physiological disorders, irregular ripening, increased susceptibility to decay, development of off-flavors, and could eventually cause the loss of the product (see Chapters 8 and 9). Most horticultural crops can tolerate extreme levels of gases when stored for only short periods (Yahia, 1998a,b, 2004). MA and CA should always be used as a compliment and never as a substitute for

proper handling techniques, especially optimum temperature and relative humidity (RH). CA storage has been restricted mainly to apples, pears, kiwifruit, and cabbage. MA and CA for transport are used for many horticultural commodities. Modified atmosphere packaging (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, cheese and some other milk products, prepared foods, dry and dehydrated foods, coffees, among others. Commercial interest in the development and implementation of MA=CA for transpor-

tation, storage, and packaging of fresh horticultural commodities (Table 1.1) will stimulate research in these areas. Economic principles of supply and demand for the commodity in relation to energy use, cost, benefit, and practicality will ultimately determine the use of MA=CA for postharvest maintenance of horticultural commodities (see Chapter 21). Continued technological developments in the future to provide MA=CA during storage, transport, and packaging at a reasonable cost are essential to greater applications on fresh horticultural commodities and their products (see Chapter 23). There are basic biologically defined limits to environment that can be employed for the

postharvest preservation of fresh horticultural commodities. The basic processes of transpiration, respiration, and biochemical transformations may continue in much the same manner in plant tissues after harvest as before harvest. However, this is done without replenishment of reserves or metabolic control from the parent plant. The nature of these cellular processes can be altered, and the chemical reaction rate can be attenuated or stimulated by manipulating the temperature and concentration of the biologically active gases such as water vapor, O2, CO2, and ethylene among others. Beyond certain limits of temperature and gas atmosphere composition and according to the nature and stage of development of the commodity, physiological disorders may develop, which terminate the useful life of the commodity by destroying appearance, flavor, nutritive value, or wholesomeness. Development and application of successful postharvest preservation techniques

TABLE 1.1

Classification of Fruits and Vegetables According to Their CA Storage Potential at Optimum Temperatures and Relative Humidities

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