Introduction

Fresh fruits and vegetables have been a part of the human diet since the dawn of history, while farmers and food sellers have been concerned about losses since agriculture began. While fruits and vegetables have always provided variety in the diet through differences in color, shape, taste, aroma, and texture [1], their full nutritional importance has only been recognized in recent times.

Contamination of fresh produce with pathogenic agents may occur at any point during production, harvesting, packing, processing, distribution, or marketing. Therefore, all fresh harvested commodities need to be free of disease agents, insects, synthetic chemicals, and cleaned of dirt or dust before being sent to the markets. The problem of how much food is lost after harvest

This chapter is dedicated to the late Mr. Erwin Fisher: an expert on scanning electron microscopy analysis, who contributed significantly to the understanding of the mode of action of hot water rinsing and brushing.

by inefficient processing, spoilage, insects and rodents, or other factors takes on greater importance as world food demand grows. Marketing of produce has also benefited from an international trend towards fresh natural foods, which are perceived to be superior to processed foods and to contain fewer chemical additives.

Although fresh produce is generally not considered a common source of foodborne illness, the incidence of this problem is increasing [2]. In recent years the number of cases of illness linked with eating fruits and vegetables has risen from 2% to about 8% of reported cases. The increased incidence may be related to changing patterns of food consumption, recognition of new means for transmission of disease organisms, emergence of pathogens that can cause infections at very low doses, an expectation that most foods distributed in any country are safe, and/or a perception that foodborne illness does not occur at home.

For many years chemical treatments have been the basis for ensuring post-harvest quality [3]. Although government authorities in each country regulate fungicide use to ensure that chemicals are not toxic at the concentrations used [4], there is still growing concern and apprehension by the public about the use of synthetic pesticides. Pressure is building for the use of alternative "nonchemical" means of disease control by the horticultural and agricultural industries.

Several chemical-free technologies to extend the storage and shelf life of fresh produce are being investigated. Among these technologies are modified atmosphere packaging [5], irradiation [6,7], use of materials that are generally regarded as safe (GRAS), such as bicarbonate salts [8] or hydrogen peroxide [9,10], hypobaric treatment [11], biological control [12], or prestorage heat treatments [13]. Heat treatment appears to be one of the most promising means for postharvest control of decay [13,14]. Prestorage heat treatments to control decay development during storage and marketing period are often applied for a relatively short time (minutes), because the targeted decay-causing agents are found on the surface or in the first few cell layers under the skin of the fruit or vegetable [14]. Heat treatments against pathogens may be applied to the fresh harvested produce in several ways: by hot water dips, by vapor heat, by hot dry air [13], and by a short hot water rinse and brush [15,16]. Hot water is an effective heat transfer medium and, when properly circulated through the load of fruit, establishes a uniform temperature profile more quickly than either vapor or dry heat [17]. Hot water treatments were originally used to control fungal diseases such as brown rot (Phytophthora spp.) on citrus fruits [18,19], but their use has been extended to achieve disinfestations from insects and alleviation of physiological deterioration [13].

Several reviews have been published on the effect of both dry and wet heat on maintenance of quality in fresh harvested crops [13,14,17,20,21]. This chapter summarizes recent research on the technologies used in hot water treatments and their effects on decay development in fruits, vegetables, and minimally processed products.

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