Vegetables

CONTENTS 17.1 Introduction ...................................................................................................................... 445 17.2 CA and MA in Vegetable Storage and Transport ...................................................... 447

17.2.1 CA Storage of Vegetables .................................................................................. 447 17.2.2 MA and CA in Vegetable Transport................................................................ 448 17.2.3 Duration of Exposure Influences Responses to MA=CA.............................. 448

17.3 CA, MA, or MAP for Vegetables .................................................................................. 449 17.3.1 Application of Modified Atmosphere Packaging to Vegetables ................. 449

17.4 Underlying Physiological and Biochemical Mechanisms Related to CA and MA Effects on Different Vegetable Tissues.............................................. 452

17.5 Innovative MAP Designs................................................................................................ 453 17.5.1 MAP Achieved via Semipermeable Film, Membrane Patch,

and Perforation.................................................................................................... 453 17.5.2 Integrating MAP into Vegetable Distribution Systems

with Fluctuating Temperature .......................................................................... 453 17.5.3 Combination Treatments ................................................................................... 453

17.6 Superatmospheric Oxygen ............................................................................................. 454 17.7 Modeling the Effects of CA, MA, and MAP on Microbiological Quality ............... 455

17.7.1 Growth of Microbial Pathogens in MAP......................................................... 455 17.8 Conclusions and Future Directions............................................................................... 457 References.................................................................................................................................... 457

Increased worldwide trade in vegetables has expanded the market for vegetables in many countries to allow year-round availability. This increased trade has been supported by expanded use of controlled atmosphere (CA) and modified atmosphere (MA) technology to maintain vegetable quality and shelf life for extended transport in marine containers and subsequent marketing periods while reducing the economic incentive for long-term stationary MA or CA storage of most vegetables since they are available with better quality from distant producers. Therefore, most current applications of MA and CA for vegetables are found in long distance transport, as well as in modified atmosphere packaging (MAP), especially of fresh-cut vegetable products, topics which are covered in Chapters 3, 4, and 18, respectively. In recent years, CA, MA, and MAP have been applied to several previously underexploited vegetables and fresh-cut vegetable products, and the

potential for using superatmospheric O2, primarily in MAP, has also been extensively evaluated. Advances have also been made in modeling the effects of CA, MA, and MAP on vegetable shelf life and microbiological quality. This chapter will provide information on recent research advances and applications of MA and CA for vegetables. It will also explore the use of vegetables to elucidate the underlying physiological and biochemical mechanisms related to CA and MA effects on produce. The amount of research on CA, MA, and MAP for vegetables has historically lagged

behind that of fruits, and of the research with vegetables, most of the effort has been expended on a few crops, i.e., lettuce (Lactuca sativa), onion (Allium cepa), and tomato (Solanum lycopersicum). The recommended CA and MA conditions for most of the vegetable crops for which such research has been conducted were reviewed by Thompson (1998), Saltveit (2003; Figure 17.1), in the commodity chapters in Bartz and Brecht (2003), and in USDA Agriculture Handbook 66 (available online at http:==www.ba.ars.usda. gov=hb66=), which contains overviews of CA (Kader, 2004) and MAP (Mir and Beaudry, 2004), as well as recommended CA conditions in most of the individual commodity chapters. Fonseca et al. (2002a) reviewed the modeling of respiration rate for the design of MAP systems for vegetables. Most research on CA, MA, and MAP involves empirical observations of changes in

various shelf life-limiting quality factors over time in experiments in which a product is placed in several combinations of gas atmospheres and sometimes also different temperatures. Reports of MAP experiments in which a vegetable product is packaged in some number of packages and shelf life observed and compared are not particularly useful unless the packaging materials were selected because they were expected to create particular desired gas atmospheres for which there is some expectation of benefit to the product.