Heat Treatment for Enhancing Postharvest Quality - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 246

Chapter 11
Heat Treatment for Enhancing
Postharvest Quality
Susan Lurie
11.1 Introduction
In a time of increased awareness among consumers that many of the chemical treatments of
fruits and vegetables to control insects, diseases, and physiological disorders are potentially
harmful to humans, much effort is being directed into developing effective, nondamag-
ing physical treatments for insect disinfestations and disease control in fresh horticultural
produce. High- and low-temperature treatments, anoxia, and irradiation are some of the pos-
sibilities being employed. These treatments are generally applied commercially for insect
and disease control. However, this chapter will discuss the additional effect of the high-
temperature treatments on commodity physiology. High-temperature treatment of fruits or
vegetables, whether it is applied for reasons of quarantine, decay control, or to affect prod-
uct physiology, will have profound effects on the metabolism of the tissue. These effects
include changes in tissue respiration, hormone production, particularly ethylene, enzyme
activities, changes in confirmation of macromolecules including protein aggregation, in
membrane components that can lead to increased membrane leakage, and other changes
that can impact of fruit and vegetable quality (Lurie, 1998). Heat treatments include hot
water dips, hot water brushing, and hot air treatments (vapor heat and forced air). All of
these have to be adapted to the commodity being treated so as to achieve the desired effect,
be it pest control, pathogen control, or direct effects on the commodity itself without causing
damage. The type of high-temperature treatment and its duration will effect how it impacts
on fruit or vegetable ripening or senescence as well as nutritional and quality attributes.
This chapter will discuss some of the studies conducted in recent years to optimize pro-
cedures for high-temperature treatments and the effect of high temperature on commodity
quality.
11.2 Effects on ripening
In climacteric fruits, which depend on ethylene for coordinated ripening, the high-
temperature inhibition of ethylene can inhibit many ripening processes, including fruit
softening, color changes, and aroma development. The synthesis of ethylene, which
synchronizes the ripening processes of climacteric fruits such as tomatoes, is inhib-
ited at temperatures near or above 35 ◦ C (Fig. 11.1). In apples heated in 38 ◦ C air,
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