Biomedical Engineering Reference
In-Depth Information
problem in early studies using calcium chloride was the reduced yield at the con-
centration (0.5%) required for improved quality and shelf life. Oxine and calcium
both reduced bacterial counts when added individually to irrigation water. The
combination treatment (50 ppm oxine + 0.25% CaCl
2
) gave the best overall results
for improving shelf life. These two chemicals are thought to act synergistically as
a result of the bactericidal activity of chlorine dioxide and the bacteriostatic effect
resulting from the reduced water activity of the mushroom surface caused by crys-
tallization of calcium chloride. Bacterial counts, browning, and rate of senescence
were all reduced by the combination treatment. Although yield is reduced with this
combination treatment, the mushrooms are significantly larger. Oxine is not currently
approved for use in mushroom irrigation water and hence recent emphasis has been
placed on determining the optimum concentration of calcium chloride in irrigation
water. The use of CaCl
2
(0.3%) reduces the bacterial blotch without reducing the
yield. Food grade gypsum (calcium sulfate) is an alternative source of calcium
because of its lower price, but the results have indicated that it has no advantage
over calcium chloride.
102
Irrigation Treatment with Biological Control
Pseudomonas tolaasii
is the major pathogenic bacterium that causes bacterial blotch
on mushrooms. This bacterium is responsible for an estimated crop loss of 5 to 10%
of mushrooms produced.
102
Chemical control of this pathogen has limitations, while
biological control was successfully used in Australia. The use of antagonistic bacteria
such as
Pseudomonas fluorescens
to control bacterial blotch was first studied in
Australia. However, the mechanism by which biological control of blotch is achieved
is still unclear.
Modified Atmosphere Packaging (MAP)
Modified atmosphere packaging (MAP) by definition is the packaging of the per-
ishable products in an atmosphere that has been modified to contain significantly
higher carbon dioxide and lower oxygen concentrations. MAP reduces the respiration
rate of mushrooms and their deterioration. Kyuper et al.
118
have used MAP combined
with CaCl
2
and obtained lower coliform and total plate counts compared with MAP
alone. In order to achieve better results, the MAP should be developed at 0°C.
111
It
is important that the O
2
concentration never falls below 2%, because according to
Sugiyama and Yang
119
storage of mushrooms in such low concentrations could create
a favorable micro-atmosphere at the center of mushrooms for growth and toxin
production of the anaerobic spore former (
Clostridium botulinum
) and therefore is
not recommended.
120
Coating with Edible Films
Many papers have been written about coating mushrooms with edible films such as
a biodegradable hydrocolloid film.
121-124
The film is intended to reduce transpiration
and evaporation, to control respiration, and to maintain a modulated atmosphere
around each individual piece of produce from the initial stages after harvest, through
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