Agriculture Reference
In-Depth Information
industry. In addition, the microorganisms entrapped in pores or stems in the calyx of
fruits will also be diffi cult to remove during a sanitation operation.
Produce Surface Properties
The chemical, physical, and topographical surface properties of fruits and vegetables
play an important role in the interaction between produce and microorganisms
(Wang 2006). For example, the cuticular waxes not only infl uence plant surface
wetability, but also alter the way the plant and microorganism interact (Beattie
and Marcell 2002). Stomata, lenticels, broken trichomes, and scars on the plants
represent natural ways of entry for microorganisms. Many live
E. coli
O157:H7
cells were found in the stomata and on cut edges of lettuce after treatment with a
chlorine solution, or in the inner tissues and stomata of cotyledons of radish
sprouts (Seo and Frank 1999; Itoh and others 1998). The ability of water and
hypochlorite wash to effectively remove bacteria is limited when the microbes
stay in protective hydrophobic pockets and folds on leaf surfaces (Adams and others
1989) or in crevices, pits, and pores (Frank and Koffi 1990; Holah and Thorpe 1990).
Han and others (2000) observed that
E. coli
O157:H7 attached more readily to coarse,
porous, and injured surfaces than to uninjured surfaces of green peppers after a
chlorine dioxide treatment. Liao and Sapers (2000) suggested that the
Salmonella
Chester attached to injured tissue and calyx cavities of the apple more easily than
to unbroken skin due to their different topographical structures and specifi c physico-
chemical properties.
Surface topography is an important physical property of fresh fruits and vegetables,
infl uencing not only their visual and sensorial aspects but also microorganism attach-
ment and removal (Liao and Sapers 2000; Han and others 2000). Published work on
quantifying the effect of surface topography on bacterial removal from fresh produce
is limited, maybe because of the diffi culties in the measurement of surface roughness
of fresh produce with suitable technologies. Traditional methods used to determine
surface roughness cannot be used to measure the soft surface of produce. A new non-
contact method was recently developed by Wang and others (2005) with confocal laser
scanning microscopy (CLSM). The roughness of Golden Delicious apples, navel
oranges, and cantaloupes was measured with the CLSM method; and a positive cor-
relation among roughness, adhesion strength of
E. coli
O157:H7, and the effi cacy of
inactivation by POAA was reported.
Aqueous Antimicrobial Treatments
Chlorine and Chlorine Compounds
As the most widely used antimicrobial for washing fresh fruits and vegetables in the
food industry (Nguyen-the and Carlin 1994), chlorine is active against a wide spec-
trum of microorganisms, including viruses, non-acid-fast vegetative bacteria, acid-fast
bacilli, bacterial spores, fungi, algae, and protozoa, with bacterial spores being the
most resistant form of microbial life (Trueman 1971). When elemental chlorine or
hypochlorites are added to water, they undergo the following reactions (Dychdala
2001 ):
Cl
+
H O
→ +
HClO
H
+
+
Cl
−
2
2
