Agriculture Reference
In-Depth Information
13
Improving Microbial Safety of Fresh
Produce Using Thermal Treatment
Xuetong Fan, Bassam A. Annous, and Lihan Huang
Introduction
Many food intervention technologies, including chemical (such as chlorine), physical
(such as ionizing radiation), and biological (such as bacterial phage) treatment methods
have been investigated for their effectiveness against human pathogens on foods. Each
of those technologies, however, has certain drawbacks. Most chemical intervention
methods are rather limited in their effectiveness to reduce the microbiological popula-
tions on the surfaces of fresh and fresh-cut produce, partially due to the inherent
cracks, crevices, pockets, and other openings that provide a protective environment
to microbes and hamper the access of many chemical sanitizers to these areas. The
formation of biofi lm and the internalization of pathogens also limit the effectiveness
of chemical sanitizers. Furthermore, there are concerns about the residues or by-
products of certain chemical sanitizers. The reluctance in consumer acceptance and
concerns about safety hamper the wide adoption of some physical intervention tech-
nologies, such as ionizing irradiation. Biocontrol agents may require the use of envi-
ronmental conditions (such as elevated temperature) that shorten the shelf life of fresh
produce. A consumer-friendly and effective technology is needed for fresh and fresh-
cut produce. Thermal treatment, a relatively simple, nonchemical alternative, has been
used by humans for thousands of years, even though the ways that heat is generated
have changed. Heat treatments do not pose signifi cant health risks from chemical
residues and, as a result, are appealing to consumers and can be used to process organic
produce. For use on fresh produce, the conditions (temperature and time) of thermal
treatments have to be developed so that the quality of fresh produce is maintained
while achieving reductions of foodborne pathogens.
As an alternative to replace the use of chemical treatments, mild heat has been used
for many years as a nonchemical postharvest treatment to control decay and to disin-
fest various fruits and vegetables (Couey 1989; Lurie 1998; Fallik 2004; Hong and
others 2007; Hu and Tanaka 2007). Furthermore, thermal treatment also has been used
to reduce the development of chilling injury for chilling-sensitive fruits and vegetables
during storage (Porat and others 2000) and to delay the ripening process by reducing
ethylene production and respiration (Paull and Chen 2000). In addition, heat treatment
also extends the shelf life of lettuce by inhibiting activity of phenylalanine ammonia
lyase and by inducing heat shock proteins, resulting in the reduction of phenolics
accumulation and tissue browning (Loaiza-Velarde and others 1997).
Thermal treatment is commonly applied in the form of hot water, high-temperature
forced air, or steam (vapor heat) to control insects and fungi in postharvest fresh fruits
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