Agriculture Reference
In-Depth Information
kiwifruits (Beuchat, 2002). Despite this, the spoilage of
minimally processed kiwifruit at 4 C is not a consequence
of microbial growth as no change in total plate count, Lac-
tobacilli, Enterobacteriaceae yeast, and molds is observed
during storage at 4 C for 4 days (O'Connor-Shaw et al.,
1994).
The proliferation of aerobic micro-organisms can be
controlled under low O 2 concentrations environment.
The growth of Pseudomonas (gram-negative aerobes)
is inhibited, more than Lactobacillus (gram-positive,
microaerophilic). High CO 2 concentrations can inhibit
the growth of most aerobic micro-organisms (especially
Pseudomonas) but is not effective in inhibiting yeasts
(Al-Ati and Hotchkiss, 2002). Therefore the application
of MA packaging with low O 2 andhighCO 2 levels
to inhibit aerobic spoilage micro-organisms has been
widely used (Farber, 1991; Nguyen-the and Carlin, 1994;
Soliva-Fortuny and Martın-Belloso, 2003). Too low O 2
concentrations could stimulate the proliferation of anaer-
obic psychrotrophic micro-organisms and could pose a
safety risk as the growth of anaerobic food-borne pathogens
might be allowed or even stimulated (Farber, 1991). MA
packaging containing argon and nitrous oxide has been
shown to be able to control the microbial population to
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Quality attributes: physical, chemical, and sensory
Physical damages (e.g., peeling, cutting, slicing, dicing, or
other mechanical injuries during preparation and process-
ing) induce physiological disorders due to plant defense
mechanism, tissue disruption facilitating direct contact be-
tween enzymes and substrates, loss of the protective epicarp
layer against microbial attack, and so on. It results in in-
creased respiration and transpiration rates, increased CO 2
and ethylene production, increased oxidative processes,
loss of solutes and moisture, tissue softening, surface dis-
coloration, generation of off flavor, and increased microbial
growth rate leading to rapid deterioration of the product
and changes in the product sensory attributes and safety
(Watada et al., 1996). Appearance, color, taste, texture, fla-
vor, nutritional value, and microbial safety are important
quality attributes related to the marketability of fresh and
minimally processed produce (Lin and Zhao, 2007). Since
the physical (size, shape, texture) and chemical (acidity,
soluble sugar content, chlorophyll content) characteristics
are related to sensory attributes (appearance for size and
shape, taste for acidity and soluble sugar content, and color
for chlorophyll content), these characteristics are discussed
further under the sensory attributes.
10 3 CFU/g up to 12 days of storage at 4 C (Rocculi et al.,
2005).
Use of citric acid to control microbial growth was sug-
gested by Senesi and Pastine (1996). Even if the acidity
level is increased by the application of organic acids, yeast
and molds can still grow. The reduction of initial microbial
count combined with low-temperature storage (at < 5 C)
can extend the shelf life of the products (O'Connor-Shaw
et al., 1994).
Roller and Seedhar (2002) have demonstrated that car-
vacrol and cinnamic acid (at concentration of 0.015%) are
effective in reducing and inhibiting microbial growth on
fresh-cut kiwifruit and honeydew melon, respectively, with-
out detrimental sensory effects. In fresh-cut kiwifruit, con-
centrations of carvacrol (0.075-0.225%) were effective in
reducing the natural microbiota of the product, but unde-
sirable color and odor changes were observed (Roller and
Seedhar, 2002).
Atmospheres with low oxygen levels inhibit the growth
of most aerobic spoilage micro-organisms; however, anaer-
obic atmosphere might allow or even stimulate growth
of anaerobic psychrotrophic, nonproteolytic clostridia. Os-
motic solutions (e.g., 65 Brix sucrose solution) can prevent
microbial adhesion in kiwifruit slices using Metschnikowia
pulcherrima as a model micro-organism (Gianotti et al.,
2001).
Appearance
Appearance is the most important quality attributes of
kiwifruits at the point of sale where purchase decision is
about to be made. The saying “we eat with our eyes” is ever
true when it comes to fresh-cut fruits, and thus appearance
is considered as the most important quality attribute
of fresh and minimally processed produce. Minimally
processed kiwifruits could be used for direct consumption
or decorative purposes (e.g., used for pavlova). Consumers
are mainly interested in a product with certain size (suitable
eating portions which may differ according to individuals
or family requirements), shape (cuts suitable for decorative
purposes and occasions requirements), characteristics
(uniform bright color surface, Fig. 25.2), and absence
of any foreign matter. During storage of minimally pro-
cessed kiwifruit products, appearance scores of kiwifruit
slices do not change significantly during storage at 4 C
(O'Connor-Shaw et al., 1994). At higher storage tem-
peratures (5 -20 C), kiwifruit slices become darker due
to enzymatic reaction and surface moisture loss, and the
tissue becomes more translucent (i.e., low ability to reflect
light) (Agar et al., 1999).
Pigments present in fresh kiwifruit and responsible
for the color perceived include xantophylls, chlorophylls,
carotenoids, and their derivatives (Leunda et al., 2000).
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