Biomedical Engineering Reference
In-Depth Information
and corn.
84
The main factors that affect longevity are moisture and temperature
85
with each 1% increase in seed moisture content (MC) halving the life of seed. This
rule applies when seed moisture content is between 5 and 14%. Below 5% MC the
speed of aging may increase because of auto-oxidation of seed lipids and above
14% MC storage fungi kill the seed. Also, for each 5°C increase in seed temperature,
the life of seed is halved (from 0 to 50°C). The presence of O
2
decreases seed
germination, even at low partial pressures
86
in dry grain because of membrane
damage caused by the production of free radicals
87
and accumulating chromosome
damage.
88
Peanut seeds with 6.2% MC stored at 38 to 40°C had unaffected germi-
nation after 26 weeks under N
2
or CO
2
atmospheres, while viability decreased
sharply in air.
89
Packaging of shelled peanuts, under vacuum or N
2
atmospheres for
distribution in Senegal after 7 months at room temperature, resulted in similar or
better germination than in other systems.
90
Saly et al.
91
indicated that storage of
shelled peanuts at room temperature and low O
2
had no significant effect on germi-
nation. Corn stored for 360 days in Mexico in hermetic storage lost germination at
the same rate as in air at 14% MC but at 15.5 and 17.6% MC viability was higher
under hermetic storage than in air at the same moisture level;
92
fungi were not present
on seeds in hermetic storage, but the
Aspergillus glaucus
group,
A. tamarii
, and
Penicillium
spp. were present on all seeds stored in air. Green gram seeds stored for
6 months at 12, 14, and 16% MC in hermetic storage had lower sugar values and
free fatty acid values than seed stored in air.
93
Bass and Stanwood
94
stored sorghum
seed for 16 years at 4, 7, and 10% MC under vacuum, air, hermetically sealed, CO
2
,
N
2
, He, or argon atmospheres at temperatures from -12 to 32°C. Under these
conditions, controlled atmosphere storage had no effect on seed germination, which
was not significantly different from that of seeds stored in hermetic containers. Seed
in air had less germination than all sealed treatments at temperatures above 0°C.
Petruzelli
95
stored wheat at 15 to 33% MC under hermetic storage and reported that
seed viability decreased more rapidly at higher moisture content, while in aerobic
storage longevity was enhanced as moisture content increased from 24 to 31% (under
hermetic storage, germination fell to 0% in 8 days at 32.7% MC and to 60% in
150 days at 15% MC). When moisture content increased above 31%, longevity was
greater under hermetic, rather than aerobic, storage. Above 24% MC at 25°C, seed
metabolism was activated and could be sustained only in the presence of O
2
. At
<24% MC O
2
had a negative effect on longevity. Wheat stored at 10.5% MC and
various combinations of N
2
, CO
2
, and O
2
for 13.5 months at 27°C showed no decline
in germination under N
2
, CO
2
, or a mixture of N
2
and CO
2
. Atmospheres of <1%
O
2
, 9 to 9.5% CO
2
, and a balance of N
2
, generated by the combustion of petroleum
fuels, does not affect germination of dry wheat, rice, or malting barley during 6-
month storage.
96
Moor
97
conducted tests in commercial silos (950 t) of malting barley
stored under N
2
(0.5% O
2
) for 5 or 9 months in Australia. There was neither a
negative nor a beneficial effect on germination. Storing unpolished rice in containers
pressurized with N
2
, CO
2
, or air had negative effects on its chemical composition.
At atmospheric temperature and pressure there was no difference in the effects of
N
2
or CO
2
on rice quality in storage.
Atmospheres of 35% CO
2
were reported to have a negative effect on the germi-
nation of wheat, soybean, and rapeseed and little effect on corn or green pea
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