Agriculture Reference
In-Depth Information
10
Irradiation Enhances Quality and
Microbial Safety of Fresh and
Fresh-Cut Fruits and Vegetables
Brendan A. Niemira and Xuetong Fan
Introduction
Foodborne illness (FBI) outbreaks associated with contaminated fruits, vegetables,
salads, and juices have risen more than fi vefold in recent decades (Sivapalasingam
and others 2004). Although preharvest (good agricultural practices, GAPs), posthar-
vest (good manufacturing practices, GMPs) and supply-chain (good handling prac-
tices, GHPs) controls can help to reduce risk, they have not been able to prevent
repeated FBI outbreaks and product recalls of tomatoes, leafy greens, melons, sprouts,
and other fresh produce. It is increasingly recognized that the lack of a broadly appli-
cable antimicrobial process (a “kill step”) is hampering the food safety efforts of the
fresh produce industry (UFPA 2007; JIFSAN 2007). Conventional thermal processes
cannot be applied to leafy vegetables without unacceptable damage, and existing
antimicrobial chemical treatments are insuffi cient to adequately reduce contamination.
An antimicrobial process that has come under increased scrutiny is irradiation.
Irradiation
is the application of controlled doses of ionizing radiation in the form
of electron beams, x-rays, or gamma rays (Table 10.1). Irradiation is a nonthermal
process that kills spoilage organisms and pathogenic bacteria in a variety of fruits and
vegetables (Thayer and Rajkowski 1999 ; Lacroix and Vigneault 2007 ). The safety and
wholesomeness of irradiated food has been demonstrated numerous times in the 60+
years that this technology has been studied (Thayer and Rajkowski 1999; FDA 2000;
Smith and Pillai 2004). In one recent example, the FDA has investigated the possibility
that furan, a putative carcinogen present in thermally processed canned foods such as
meats, soups, etc., might also be produced during irradiation. The safety of irradiation
was reaffi rmed when it was recently shown that a dose of 5 kilogray (10 kGy = 1 Mrad)
did not induce detectable levels of furan in most fresh-cut fruits and vegetables (Fan
and Sokorai 2008). Whereas furan production was above the limit of detection after
irradiation, the levels were shown to be much lower than in thermally processed foods.
Therefore, irradiation with moderate doses is as safe as thermal processing and has a
potential as one of several “hurdles” in fruit and vegetable processing (Smith and
Pillai 2004 ; Niemira and Deschenes 2005 ).
Fresh produce may be irradiated to inhibit sprouting, to delay ripening, to sterilize
or kill insect pests, or to reduce microbial populations. Until recently, in the United
States, irradiation has regulatory approval for application to produce only for insect
control, sprout inhibition, and shelf-life extension. The highest dose allowed for these
purposes is 1 kGy (Table 10.2). However, in 2008 the FDA (2008) approved the use
of irradiation up to 4.0 kGy on fresh lettuce and fresh spinach to improve food safety
191
