Biomedical Engineering Reference
In-Depth Information
by prolonging disease resistance associated with immaturity, and by directly inhib-
iting the pathogen at temperatures unfavorable to its development.
133
Precooling is
the first step in the handling of many fruits and vegetables. Hall
183
reported that in
a tropical environment, a delay of 2 h between harvesting and cooling can reduce
the shelf life of produce by a whole day. Dicecco
184
reported that mushrooms held
at 10°C have only 25 to 50% the shelf life of those held at 1°C. Chen and co-
workers
185
reported that bamboo shoots in Taiwan produced 14% more finished
product when stored at 5°C for 2 days after harvest than when held at room tem-
perature before processing. A 40% reduction in marketability of strawberries was
caused by a 4-h delay at a holding temperature of 30°C.
45
If not cooled to -0.5°C
within 24 h, “Bartlett” pears develop enzymatic breakdown known as “watery break-
down”.
186
However, there are commodities that do not require prompt cooling, such
as freestone peaches,
186
apples,
108
tomatoes,
130
and lemons.
116
The commodities do
not rapidly deteriorate but develop symptoms of chilling injury upon storage.
Methods of precooling are forced-air cooling, hydrocooling, hydro-air cooling,
and vacuum cooling, although room cooling and package icing are also common.
Choice of the precooling method is dependent on the cooling needs and suitability
of a commodity, type of packaging material used for the product, type of market
and marketing system, and economic and other considerations. Commodities and
packaging materials that cannot withstand soaking and immersion in water are not
suitable for hydrocooling, hydro-air cooling, or package icing. Vacuum cooling can
be used on commodities that have a favorable surface-to-mass ratio like leafy and
flower-type vegetables, celery, some sweet corn, and bell peppers.
186
About 1%
weight loss is incurred for each 6°C cooled in vacuum cooling.
187
Generally, room
cooling can be used for all kinds of fruits and vegetables including strawberries and
grapes, although it is not recommended for commodities that deteriorate rapidly.
Yahia and Sanudo
61
recommended forced-air precooling of avocados to temperatures
of 8 to 10°C. Prompt cooling of table grapes is crucial in preventing the softening
of berries and weight loss of stems, which easily break when handled dry. Table
grapes are precooled to about 2°C by forced air cooling,
45
which is also ideal for
strawberries because of the short period needed. For sweet corn destined for the
fresh market, hydrocooling is the method recommended,
188
where crates packed with
4 to 5 dozen ears pass through a spray of cold water. Half-cooling times of 28 min
for sweet corn packed 5-ears deep in wire-bound crates have been reported. Storage
life can be extended from 4 to 8 days as a result of precooling when maintained at
a temperature of 0°C and relative humidity of 90 to 95%. Contact icing of loaded
trucks also provides a means of precooling and minimizing quality losses during
transportation. Brusewitz and co-workers
189
studied the different cooling methods
to extend the shelf life of peaches. They also studied the effect of picking times on
the measured variables like weight loss, impact parameters, and bruising. It was
confirmed in their study that cooling at recommended conditions (temperature of
4°C and relative humidity of 92 to 94%) was beneficial for extended storage life
and reducing weight loss and bruise damage that limit marketability of the produce.
Evidently, peaches need humid cool air coupled with hydrocooling before storage
to minimize deterioration. Peaches picked on hot afternoons were affected adversely
Search WWH ::
Custom Search