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2008 International Grain Quality & Technology Congress Proceedings
0
S
TORAGE
O
F
C
ORN
,
W
HEAT
S
OYBEAN
A
ND
S
UNFLOWER
I
N
H
ERMETIC
P
LASTIC
B
AGS
Bartosik
1
, Ricardo, Juan Rodríguez
1
and Leandro Cardoso
1
EEA INTA Balcarce, Ruta 226 km 73,5, Balcarce (7620), Pcia. Bs.As, Argentina
rbartosik@balcarce.inta.gov.ar, jrodriguez@balcarce.inta.gov.ar, lcardoso@balcarce.inta.gov.ar
A
BSTRACT
This research makes focus on the effect of grain moisture content (MC) and storage time on the
quality of corn, wheat, soybean and sunflower stored in hermetic plastic bags of 200 tonnes of
capacity.
Grain samples were periodically collected during the entire storage time, and then quality tests
were performed. Additionally, moisture content stratification and temperature changes were
monitored for different grain layers. The study also included measurement of CO
2
and O
2
concentration of the interstitial atmosphere.
The main results indicated that the grain temperature in the hermetically sealed plastic bags
followed the pattern of the ambient temperature throughout the year.
The average moisture content did not significantly change during the entire experiment for both
dry and wet silo-bags. In general, no MC stratification was observed but in wet sunflower, where
the top layer increased MC from 16.4 to 20.8% after 150 days of storage.
When the grain was stored at the market moisture content, no significant decrease in the quality
parameters could be observed during 150 days of storage. Contrastingly, when grain was stored
above the market moisture content, the decrease in some of the quality parameter could be
observed.
The increase in the CO
2
concentration was higher at the end of the storage time and also was
higher in those bags with wetter grain. Measurement of gas composition in the interstitial air could
be used as an indication of the biological activity of the grain mass in the hermetic storage
systems, and a tool for monitoring grain storability.
Keywords: Modified atmosphere, Grain, Quality.
I
NTRODUCTION
In Argentina, 95 million tonnes of wheat, corn, soybeans and sunflower were harvested in 2006/07
(SAGPyA, 2007). At the same time, the total permanent storage capacity of the country was
estimated between 65 and 70 million tonnes, resulting in a shortage in storage capacity of about 25
to 30 million tonnes (PRECOP, 2007). Due to this insufficient storage capacity, an important
proportion of the Argentine grain production had to be delivered directly from the field to the
regional grain elevators and from there to the terminal ports. Other consequences are an
insufficient truck fleet to transport the harvested crop from the field to the elevators, and terminal
ports working at 100% of their capacity. On top of that, trucks are used as temporary storage at the
terminal ports in long lines. As a result, grain producers have to pay higher prices for
transportation and services at the elevator (drying, cleaning, etc) during the harvest time than
2008 International Grain Quality & Technology Congress Proceedings
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during the off season. This inefficiency of the grain post-harvest system influenced the harvest
operations and farm logistic, which increased production cost unreasonably.
To overcome these unfavorable circumstances, grain producers started to increase their on-farm
storage capacity. By doing so, grain producers were able to store their grain on-farm and sell it
after the harvest season, when not only the grain prices are usually higher, but also the service
costs are lower. However, to build a new storage facility or update/enlarge an existing one is
generally not affordable for most Argentine farmers. The main constraints are the high initial
investment, high interest rate and short loan maturation period. Under these circumstances, a new
storage technique has gained popularity among farmers. This technique has been on the market for
many years for storing wet grain for feed (grain silage) and then was adapted for storing dry grain.
It consists of storing grain in hermetically sealed plastic bags (“silo-bags”). Each bag can hold
approximately 200 tonnes of grain and with the available handling equipment is very easy to fill.
Local companies also developed machineries to unload the plastic bag transferring the grain
directly to the track or wagon. The new generation of high capacity combines found in the silo-bag
system the ideal partner, since the loading capacity of the bagging machine is basically limited to
the transportation capacity between the combine and the place where the bag is filled. Other
advantage of the silo-bags is that they can be easily incorporated into grain identity preservation
(IP) programs. Silo-bags can be easily set up in the field, right next to the crop, reducing risks of
contamination of the specialty grain with other commodities. Many wheat growers have found in
the silo-bag system the ideal tool to segregate different wheat varieties directly in the field.
In 2001, around 2 million tonnes of grain (corn, wheat, soybean and sunflower) were stored with
this system. During the past few years, this storage technique has been further refined and the
“silo-bag” system has gained rapid adoption among Argentine farmers, up to the point that in year
2007 about 22-25 million tonnes were stored in the silo-bags systems (more than 23 % of the total
production).
These plastic bags are waterproof and have certain degree of gas-tightness (O
2
and CO
2
). As a
result, respiration of the biotic components of the grain mass (fungi, arthropods, and grain)
increases CO
2
and reduces O
2
concentrations.
The effect of low oxygen concentration on insects is called anoxia. Oxygen level below 3% is
required for effective control of insects (below 1% if rapid killing is required) (Banks and Annis,
1990 and Adler et al., 2000). The effect of high carbon dioxide concentration is called hypercarbia.
The exposure time required to achieve complete control of insects is inversely proportional to CO
2
concentration. The minimum CO
2
concentration required to achieve total insect control seems to
be 35%, with an exposure time longer than 14 days. However, different insect species have
different tolerance to hypercarbia, as well as the insect stage (Navarro and Donahaye, 2005).
Under self modified atmospheres treatments, the increase on the CO
2
concentration corresponds to
a decrease in the O
2
concentration, so a combined effect is obtained and insect killing could be
achieved more easily due to a synergistic effect (Calderon and Navarro, 1980). Additionally, the
plastic material proved to be an efficient physical barrier that prevents insects from getting into the
grain bag.
Low O2 concentration (below 1%) seems to be not sufficient to stop mold growth, although grain
deterioration was delayed. Increasing CO2 concentration from 3 to 30% (even with O2
concentrations of 21%) resulted in a reduction of fungal counts. The combination of high CO2 and
low O2 concentrations retarded mold growth. The latent period for growth of storage fungi in low
O2 concentration (less than 1%) were longer than of the field fungi. However, the storage fungi
were much tolerant to low a
w
(low equilibrium relative humidity) than were the field fungi. When
2008 International Grain Quality & Technology Congress Proceedings
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the CO2 concentration increased to 15%, the lag phase of field and storage fungi increased for all
a
w
levels (Navarro and Donahaye, 2005). Wilson and Jay (1975) reported that mold appeared later
in grain stored under modified atmosphere storage condition compared to control.
Aerobic fungi are predominant in bulk grain, and they find suitable conditions for proliferating
and multiplying under normal atmosphere composition. However, low O2 and high CO2
concentration reduces (even suppresses) the viability of the fungi, expressed as rate of growth,
degree of sporulation, respiratory rate and finally their ability to attack grain tissues (Navarro and
Donahaye, 2005).
The ability of A. flavus to produce aflatoxin in groundnuts under optimal temperature and
moisture conditions for mold growth was substantially reduced with the increase on CO2 and
decrease on O2 concentrations. The primary cause of inhibition was the high CO2 concentration,
rather than the low O2 concentration, and after the colonies were returned to normal atmosphere,
mycotoxins can be produced (Landers et al., 1986).
The effect of high CO2 concentration on seed viability was studied, and it was observed that seeds
below their critical moisture content (MC) are not significantly affected at high CO2 or low O2
concentration (Banks, 1981). However, seed stored at high MC could result with reduction in the
germination test due to the interfering effect of the CO2 with the enzymatic activity of glutamine-
decarboxylase (Münzing and Bolling, 1985). It was observed that the negative effect of CO2 was
more pronounced with temperatures above 47°C, but this effect was not noticeable with
temperatures bellow 30°C (Banks and Annis, 1990). Seeds stored in the silo-bags usually have
temperatures below 30°C, thus it should not be expected a noticeable reduction on seed viability
due to high CO2 concentration.
The National Institute of Agricultural Technologies (INTA) of Argentina has been conducting
research on storage of grain and oilseed in hermetic plastic bags since year 2000 (Bartosik et al.,
2002). The main goals of these experiments were to study the effect of MC, temperature and
storage time on quality of corn, wheat, soybean and sunflower.
M
ATERIALS AND
M
ETHODS
The tests were carried out on farms in the south east of Buenos Aires province, Argentina. The
dimensions of the bags were 67 m long (220 ft), 2.74 m diameter (9 ft), and 235 microns thick.
The bags are made of a plastic material with three layers, black on the interior side and white on
the exterior (Figure 1). This material is airtight and does not allow water and/or gasses to pass in
or out. Each bag held roughly 200 tonnes of wheat, corn and soybean, and 120 tonnes of
sunflower. The bags were filled with fresh grain right after the harvest, in the same plots were the
crops were planted.
2008 International Grain Quality & Technology Congress Proceedings
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Figure 1. Picture of a 200 tonnes capacity (60 m long and 2.74 m diameter) hermetic storage plastic bag (silo-
bag).
The grain stored in plastic bags was sampled at the beginning of the experiment and after 45, 80,
and 150 days. Samples were taken with a simple truck probe. The plastic cover was punctured at
three locations along the length of the bag. At each one of these locations grain was sampled at
three different levels (surface= 0.10 m depth, middle= 0.75 m depth, and interior= 1.6 m depth.
Total height of the bag= 1.7 m). Material from each one of the three sampling locations was
segregated by level (surface, middle, and interior). Then, grain from superior level of each
sampling location was blended all together, conforming a compounded sample for superior level.
The same procedure was applied to samples from middle and interior levels. After probing the
bags, the holes were sealed with special plastic tape to keep the system hermetically sealed. In
order to track any change in the quality of the grain, several quality tests were performed on each
of the sub samples (test weight, germination test, composition, oil acidity for soybean and
sunflower, and baking quality for wheat). The MC of the grain at different levels was monitored,
as well as the grain temperature. MC was determined by oven drying at 103 ºC for 72 h (ASAE,
1983). Temperature was monitored by dataloggers every 10 minutes during the experimental
period. Carbon dioxide (CO
2
) and oxygen (O
2
) levels at different depths were also monitored after
5 and 100 days of storage time using a fast gas analyzer (ABISSPRINT, Abiss, Viry Chatillon,
France). The effect of the modified atmosphere on insect activity was also investigated. Bags
made of fine a plastic mesh containing grain (wheat) and 50 rice weevils (Sitopillus orizae (L.))
were placed in a plastic pipe with holes to facilitate gas flow between the interstitial grain air in
the grain bulk and the inside of the pipe. These pipes were inserted into the grain mass extending
through the three depths (surface, medium and interior). For each depth and sampling date three
replicates were analyzed.
The wheat experiment started on January 2
nd
, 2001 (variety ProINTA-Isla Verde). One bag was
filled with dry wheat (12.5%) and the other with wet wheat (16.4%). After the bags were filled, the
ends were sealed and the grain was not disturbed until the end of the test on June 4
th
(150 days).
The sunflower experiment started on March 8
th
, 2001 (hybrid Van der Haven 480). One bag was
filled with dry sunflower (8.4%) and the other with wet sunflower (16.4%). The grain was hold in
the bags during 160 days (August 15
th
).
2008 International Grain Quality & Technology Congress Proceedings
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The corn experiment started on July 6
th
, 2001 (hybrid Axel, Sursem). One bag was filled with dry
corn (14.8%) and the other with wet corn (19.5%). The grain was hold in the bags during 153 days
(December 5
th
).
The soybean experiment started on June 5
th
, 2001 (variety Nidera 4100). One bag was filled with
dry soybean (12.5%) and the other with wet soybean (15.6%). The grain was hold in the bags
during 160 days (November 12
th
).
R
ESULTS AND
D
ISCUSSION
Temperature
The main results indicated that the grain temperature in the hermetically sealed plastic bags
followed the pattern of the average ambient temperature. For instance, when wheat is harvested
and bagged in the early summer (January), the grain temperature starts with a maximum and then
decreases, following the drop of the ambient air temperature during the fall, and reaching the
minimum during the winter (June) (Figure 2). On the other hand, when corn is harvested and
bagged in the late fall or winter, the grain temperature starts with a minimum and then increases
following the rise of the ambient air temperature during the spring, and reaching the maximum
during the summer (Figure 3).
The silo-bags with wheat and sunflower were set up during the summer time, with grain
temperatures close to 40°C and 30°C respectively. The silo-bag was able to dissipate the
accumulated heat in the grain to the ambient air and the soil in a couple of months. This could be
explained with the relation volume/surface, which is substantially lower for silo-bags (0.7 for a
200 tonnes silo-bag) than for a regular bin of similar storage capacity (1.27 for a 7 m diameter and
9 m height bin of 200 tonnes of capacity). Wheat and sunflower harvested in summer time reached
the safe storage temperature for preventing insect development (below 17°C) by early May
(Figure 2), while soybean and corn, harvested during the fall and winter, were able to maintain the
temperature below 17°C until early November (Figure 3).
2008 International Grain Quality & Technology Congress Proceedings
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0
5
10
15
20
25
30
35
40
45
50
1/2/01
1/13/01
1/23/01
2/3/01
2/13/01
2/24/01
3/6/01
3/17/01
3/27/01
4/6/01
4/17/01
4/27/01
5/8/01
5/18/01
5/28/01
Date
Temperature (°C)
Ambient
Superior
Middle
Bottom
Figure 2. Temperature pattern at different grain depths (surface, middle and bottom) during storage of wheat
in a silo-bag, from January to June.
2008 International Grain Quality & Technology Congress Proceedings
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-10
0
10
20
30
40
50
8/23/01
9/9/01
9/26/01
10/12/01
10/29/01
11/15/01
12/1/01
12/18/01
1/4/02
1/20/02
Date
Temperature
Ambient
Superior
Middle
Bottom
Figure 3. Temperature pattern at different grain depths (surface, middle and bottom) during storage of corn in
a silo-bag from August to January.
At the surface of the grain, the temperature showed the distinctive pattern of the ambient air
temperature, reaching its maximum at noon and minimum during the early morning (Figures 2 and
3). The daily temperature oscillation decreased with the grain depth, being not noticeable after 0.7
m depth. The larger temperature change at the surface level could cause moisture change due to
water condensation (during the night) and relative humidity change at the interstitial air close to
the grain surface.
Moisture Content
Tables 1 and 2 show the MC of the grain at three different levels (top: 0.1 m from the surface,
middle: 0.75 m from surface, and bottom: 1.5 m from surface) at the beginning of the experiment
and after 150 days of storage. The average MC did not substantially change during the entire
experiment for both dry and wet silo-bags, and most of the differences could be explained by the
precision of the moisture meter and the experimental error during the sampling operation. It was
not observed, in general, a substantial moisture stratification during storage, with the exception of
the wet sunflower silo-bag. For this grain, the MC at the top layer increased from 16.4% to 20.8%
during the experiment. The substantial MC increase at the top grain layer could be caused by
repeated cycles of water condensation at the top grain layer. The equilibrium relative humidity of
16.4% MC sunflower is above 90% at 15°C. With the temperature decrease during the night, the
relative humidity could easily increase up to 100% and condensate on the grain surface and plastic
cover, increasing, in the long time, the grain MC at the top layer. This condition of high MC (and
high RH%) at the top grain layer created suitable conditions for developing of yeast and other
anaerobic microorganisms, which are not normally observed when dry grain is stored.
2008 International Grain Quality & Technology Congress Proceedings
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Table 1. Moisture content of the dry grain silo-bags at three different levels (top: 0.1 m from the surface,
middle: 0.75 m from surface, and bottom: 1.5 m from surface) at the beginning of the experiment and after 150
days of storage.
Position Wheat Corn Soybean Sunflower
Initial Final Initial Final Initial Final Initial Final
Top 12.5
13.5
14.8
14.2
12.5
12.9
8.4
8.3
Middle 12.5
13.4
14.8
14.5
12.5
12.6
8.4
8.6
Bottom 12.5
12.9
14.8
14.5
12.5
12.6
8.4
9.6
Table 2. Moisture content of the wet grain silo-bags at three different levels (top: 0.1 m from the surface,
middle: 0.75 m from surface, and bottom: 1.5 m from surface) at the beginning of the experiment and after 150
days of storage.
Position Wheat Corn Soybean Sunflower
Initial Final Inicial Final Initial Final Initial Final
Top 16.4
15.7
19.5
18.8
15.6
15.7
16.4
20.8
Middle 16.4
16
19.5
18.8
15.6
15.6
16.4
17.6
Bottom 16.4
16.1
19.5
18.7
15.6
15.5
16.4
15.5
Grain Quality
In general for all grains, when the grain was stored at the market MC (or below market MC), no
significant decrease was observed during 150 days of storage for most of the quality parameters
considered. However, some quality parameters such as germination test, resulted slightly affected.
Contrastingly, when grain was stored above the market MC corresponding to the grain, a certain
degree of decrease in some of the quality parameter was observed (from almost noticeable to
severe) after 150 days of storage.
Table 3 shows the effect of storage time on dry and wet wheat quality parameters. When wheat
was bagged at 12.5% MC no substantial reduction in test weight was observed, while the
germination test decreased from 93 to 87%. This 6 percentage points of reduction did not prevent
the use of the stored wheat as seed for the following planting season (in Argentina farmers are
allowed to store their own seed for the next planting season, and this is a common practice). The
baking quality parameters for dry wheat did not substantially change after 150 days of storage,
making suitable this storage technology for storing wheat for flour milling purpose.
When 16.4% MC wheat was bagged in January, the ambient temperature was in the low 40’s, so
the average grain temperature was close to 42°C. The combination of high MC and high
temperature resulted in a substantial decrease on most of the quality parameters evaluated. The test
weight decreased from 78.7 to 77.3 kh/hl, although this decrease did not change the commercial
grade of the wheat. The germination test decreased from 95 to 40%, which prevented the use of
the grain as seed for the next planting season. Additionally, all the baking quality parameters
resulted negatively affected, making this wet wheat not suitable for flour milling purposes.
Wheat is harvested during the early summer (December-January), with ambient air temperatures
above 30°C. Thus, wheat is usually bagged at 30°C or more, and stored through all summer and
early fall with relatively high temperatures, before the ambient temperature starts to cool down in
the late fall and winter. Therefore, the combination of high storage temperature and grain MC
results in high biological activity, with the subsequent negative effect on wheat quality parameters
2008 International Grain Quality & Technology Congress Proceedings
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during storage. On the other hand, storage of wheat during 5 months with low MC (below 14%)
results a safe storage condition.
Table 3. Wheat quality parameters at the beginning of the experiment and after 150 days of storage in hermetic
plastic bag.
Sampling time Test
weight
(kg/hl)
Baking quality parameters
Germination
test (%)
Gluten
(%) W P/L Abs.
a
LV
(cm
3
)
b
SV
c
Dry Wheat (12.5%)
Initial 82.4 93.0 30.2 282 0.9 61 620 4.3
Final (150 days) 82.0 87.0 27.8 313 1.1 62 655 4.5
Wet Wheat (16.4%)
Initial 78.7 95.0 29.8 288 1.0 61 675 4.7
Final (150 days) 77.3 40.0 22.6 283 2.6 61 578 4.0
References:
a
= Water absorption,
b
= Loaf volume,
c
= Specific volume
Table 4 shows the effect of storage time on dry and wet corn quality parameters. The grain bagged
at 14.8% MC resulted with a slightly higher test weight after 150 days of storage, while the
percentage of damaged kernels increased by 1.3 percentage points. Since the initial dry corn
samples were above the damaged kernel tolerance for the argentine standard (3%), the change in
this quality factor did not affect the commercial grade of corn.
The wet corn samples (19.5% MC) resulted with a reduction in the test weight of 2 kg/hl, and a
substantial increase of the damaged corn faction of 4.4 percentage points.
Corn is harvested during the fall, with decreasing ambient air temperatures. Thus, corn is usually
bagged at 20°C or less, and stored during the winter with ambient air temperatures below 15°C
average. As a result, wet corn (18% MC) is usually stored without substantial decrease in quality
parameters until spring (September), because the grain remains at 15°C or below. Thereafter, with
the temperature increase during spring increases the biological activity inside the silo-bag,
resulting in substantial deterioration of the corn quality parameters during late spring. Storage of
dry corn (below 15%) during 5 months results in a safe practice, while storage of wet corn beyond
winter time (more than 3 months), usually results in negative effects on grain quality parameters.
Table 4. Corn quality parameters at the beginning of the experiment and after 150 days of storage in hermetic
plastic bag.
Sampling time (days) Test weight (kg/hl) Damaged kernels (%)
Dry Corn (14.8%)
Initial 73.0 3.2
Final (150 days) 74.0 4.5
2008 International Grain Quality & Technology Congress Proceedings
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Wet corn (19.5%)
Initial 72.0 5.8
Final (150 days) 70.0 10.2
Table 5 shows the effect of storage time on dry and wet soybean quality parameters. The soybean
bagged at 12.5% MC did not substantially modify the test weight and oil percentage of the
samples. On the other hand, the oil acidity index and the germination test were, somehow,
affected. The decrease on germination test (from 74 to 62%) indicated that precautions should be
taken when the soybean is to be used as seed for the next planting season. In Argentina, the base
MC for soybean commercialization is 13.5%. According to the Modified Chung-Pfost EMC
equation and the parameters available in the ASABE D245.5 standard, the equilibrium relative
humidity of 67% (considered the safe storage MC) corresponds to a MC substantially below
13.5% (Figure 4). Thus, if soybean will be stored in plastic bags to be used as seed in the next
planting season, the bagging MC should be below 12.5% MC.
11
11.5
12
12.5
13
13.5
0 5 10 15 20 25 30
Grain Temperature (°C)
Safe Stoarge MC (%)
Figure 4. Safe storage MC (equilibrium relative humidity of 67%) for soybean at different storage
temperatures [Modified Chung-Pfost equation and ASABE D245.5 parameter standard].
The wet soybean samples (15.6% MC) resulted with a reduction in the test weight of 2 kg/hl, and
a substantial increase of the damaged corn faction of 4.4 percentage points.
Soybean is harvested like corn, during the fall, with decreasing ambient air temperatures. Thus,
soybean is usually bagged at 20°C or less, and stored during the winter with ambient air
temperatures below 15°C average. As a result, wet soybean (above 13.5% MC) is usually stored
without substantial decrease in quality parameters until spring (September), because the grain
remains at 15°C or below. Thereafter, with the temperature increase during spring, increases the
2008 International Grain Quality & Technology Congress Proceedings
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biological activity inside the silo-bag, resulting in substantial deterioration of the soybean quality
parameters during late spring. Storage of dry soybean (below 13.5%) during 5 months results in a
safe practice (excepting for maintaining the germination test values, which requires storing
soybeans below 12.5%), while storage of wet soybean beyond winter time (more than 3 months),
usually results in negative effects on grain quality parameters.
Table 5. Soybean quality parameters at the beginning of the experiment and after 150 days of storage in
hermetic plastic bag.
Sampling time (days) Germination
test (%) Test weight
(kg/hl) Oil composition
(%) Oil acidity
index (%)
Dry Soybean (12.5%)
Initial 74.0 71.0 20.8 1.6
Final (150 days) 62.0 71.0 20.5 1.9
Wet Soybean (15.6%)
Initial 74.0 68.5 21.5 1.7
Final (150 days) 55.0 68.9 21.0 2.3
Table 6 shows the effect of storage time on dry and wet sunflower quality parameters. When
sunflower was bagged at 8.4% MC no reduction in oil composition was observed, while the oil
acidity index slightly increased from 0.9 to 1.4. This increase in the oil acidity index did not affect
the standard grade of sunflower, since the oil acidity index limit for the argentine standard is of
1.5% until August 31, and 2% thereafter. Thus, storage of dry sunflower (below 11% MC) is a safe
practice, since the industrial quality parameters were not affected after 150 storage days.
Storing of wet sunflower (16.4%) resulted in a reduction of oil composition of 1.3 percentage
points (from 47.0 to 45.7%) after 150 storage days, and a more substantial increase in the oil
acidity index (0.9 to 3.9%).
Sunflower is harvested during the late summer (February), with ambient air temperatures above
20°C. Thus, sunflower is usually bagged at 20-25°C or more, and stored through the late summer
and early fall with relatively high temperatures, before the ambient temperature starts to cool
down in the late fall and winter. Therefore, the combination of relatively high storage temperature
and grain MC results in high biological activity, with the subsequent negative effect on industrial
sunflower quality parameters during storage. On the other hand, storage of sunflower during 5
months with low MC (below 11%) results a safe storage condition.
Table 6. Sunflower quality parameters at the beginning of the experiment and after 150 days of storage in
hermetic plastic bag.
Sampling time (days) Oil composition (%) Oil acidity index (%)
Dry Sunflower (8.4%)
Initial 49.0 0.9
Final (150 days) 49.0 1.4
Wet Sunflower (16.4%)
Initial 47.0 0.9
2008 International Grain Quality & Technology Congress Proceedings
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Final (150 days) 45.7 3.9
Atmosphere Composition
Grain and associated microorganism respiration produces an increase in the CO
2
concentration and
reduction in the O
2
concentration. Tables 7 to 10 show the change in the interstitial atmospheric
composition during storage time for dry and wet wheat, corn, soybean and sunflower. The increase
in the CO
2
and reduction in the O
2
concentrations were higher at the end of the storage time. It was
also observed that, for any grain, the increase in the CO
2
and reduction in the O
2
concentrations
were higher for the wet than for the dry grain silo-bags, with the exception of corn, where both
silo-bags presented similar values of CO
2
and O
2
(Table 8). The higher CO
2
concentration
observed in the wet grain plastic bag was an expected result, since the higher grain MC is able to
support higher biological activity (mold growth). Thus, the higher respiration rate resulted in a
more substantial modification of the interstitial atmosphere. In the case of the corn experiment,
where the dry and wet corn plastic bag resulted with high and similar CO
2
concentration (about
18%), it was speculated that the dry corn plastic bag had a portion of the grain in decomposition
(most likely due to breakages in the plastic film at the bottom caused by the stems of the former
crop, which often allow water coming inside the bag). The CO
2
and O
2
concentrations in the wet
sunflower plastic bags reached 70.3 and 4.9%, respectively (Table 10). This significant change in
gas composition was most likely caused by the high biological activity that 16.4% MC sunflower
can support (the safe storage MC for sunflower is below 11%). Thus, measurement of gas
composition in the interstitial air could be used as an indication of the biological activity of the
grain mass in the hermetic storage systems, and a tool for monitoring grain storability.
Table 7. Change during storage time of carbon dioxide (CO
2
) and oxygen (O
2
) concentrations in the interstitial
atmosphere of wheat stored in the silo-bag.
5 days 100 days Grain Condition
CO
2
O
2
CO
2
O
2
Dry wheat (12.5%) 4.4 14.7 13.0 10.4
Wet wheat (16.4%) 18.9 5.5 22.8 5.6
Table 8. Change during storage time of carbon dioxide (CO
2
) and oxygen (O
2
) concentrations in the interstitial
atmosphere of corn stored in the silo-bag.
20 days 35 days 52 days 79 days 84 days Grain Condition
CO
2
O
2
CO
2
O
2
CO
2
O
2
CO
2
O
2
CO
2
O
2
Dry corn (14.8%) - - 9.7 10.4 18.2
2.1 18.2
2.1 - -
Wet corn (19.5%) 6.2 12.8 - - - - - - 18.5 2.6
2008 International Grain Quality & Technology Congress Proceedings
12
Table 9. Change during storage time of carbon dioxide (CO
2
) and oxygen (O
2
) concentrations in the interstitial
atmosphere of soybean stored in the silo-bag.
30 days 46 days 93 days 160 days Grain Condition
CO
2
O
2
CO
2
O
2
CO
2
O
2
CO
2
O
2
Dry soybean (12.5%) 3.5 15.5 3.8 14.2 4.5 11.3 7.5 10.0
Wet soybean (15.6%) 5.7 7.7 6.8 5.2 9.2 4.8 16.2
3.0
Table 10. Change during storage time of carbon dioxide (CO
2
) and oxygen (O
2
) concentrations in the
interstitial atmosphere of sunflower stored in the silo-bag.
34 days 125 days Grain Condition
CO
2
O
2
CO
2
O
2
Dry sunflower (8.4%) 16.5 5.1 18.9 4.5
Wet sunflower (16.4%) 70.3 4.9 69.1 4.7
C
ONCLUSION
The temperature of the grain stored in the hermetic plastic bags followed the typical pattern of the
average ambient temperature throughout the season. No temperature rise due to biological activity
was observed (even in wet grain storage). Grain stored in the plastic bag remained below 17°C
(temperature limit for insect development) during the cold part of the year.
The average MC of the grain mass did not change during storage. Moisture stratification was
observed in wet sunflower, which increased MC at the surface from 16.4 to 20.8% during more
than 150 days of storage.
In general, when grain was stored at the market MC or below (14% for wheat, 14.5% for corn,
13.5% for soybean and 11% for sunflower), no significant decrease in the quality parameters was
observed after 150 days of storage. When grain was stored wet (above market MC), a decrease on
one or more quality parameters was observed, and that decrease was more severe for higher MC
grain. The combination of high grain temperature (warm part of the year) and high MC resulted in
greater quality loss.
CO
2
concentration increased during storage time for all grains. Wet grain had a higher degree of
modification of the interstitial atmosphere, due to the higher biological activity. Measurement of
gas composition in the interstitial air could be used as an indication of the biological activity of the
grain mass in the hermetic storage systems, and a tool for monitoring grain storability.
Acknowledgements
The authors want to thank Ing. Hector Malinarich and Ing. Gabriel Alfonzo for helping in the field
work of this research, and to the hermetic plastic bags manufacturing companies (Ipesa SA, Plastar
SA and Agrinplex) for the financial support of our research in modified atmospheres.
2008 International Grain Quality & Technology Congress Proceedings
13
R
EFERENCES
1. Adler, C., H.G. Corinth and C. Reichmuth. 2000. Modified atmospheres, pp. 106-146, in Bh.
Subramanyam and D.W. Hagstrum (Eds.), Alternative to Pesticides in Stored-product IPM.
Kluwer Academic Publisher, Boston, USA.
2. ASAE Standards. 2001. ASAE D241.5. Moisture relationships of plant-based agricultural
products. St. Joseph, Michigan, USA.
3. Banks, H.J. 1981. Effects of controlled atmosphere storage on grain quality: a review. Food
Technol. Aust. 33:335-340.
4. Banks, H.J. and P.C. Annis. 1990. Comparative advantages of high CO2 and low O2 types of
controlled atmospheres for grain storage, pp. 93-122, in M. Calderon and R. Borkai-Golan
(Eds.), Food Preservation by Modified Atmospheres, CRC Press, Boca Raton, Florida, USA.
5. Bartosik, R. E., J.C. Rodriguez, H.E. Malinarich, and D. E. Maier. 2002. “Silobag”:
evaluation of a new technique for temporary storage of wheat in the field. Proceedings of the
8th International Working Conference on Stored Product Protection, pages 1018-1023, York,
England.
6. Calderon, M. and S. Navarro. 1980. Synergistic effect of CO2 and O2 mixture on stored grain
insects, pp. 79-84, in J. Shejbal (Ed.), Controlled Atmosphere Storage of Grains. Elsevier,
Amsterdam.
7. Landers, K.E., N.D. Davis and U.L. Diener. 1986. Influence of atmospheric gases on aflatoxin
production by Aspergillus flavus in peanuts. Phytopathology 57: 1967.
8. Münzing, K. and H. Bolling. 1985. Qualitatsveranderungen von Weizen durch CA-Lagerung.
Verjffentlichungsnr. 5309 der Bundesforschungssanst. Für Getreide- und
Kartoffelverarbeitung, Detmold, 22 S.
9. Navarro S. and J. Donahaye. 2005. Innovative environmentally friendly technologies to
maintain quality of durable agricultural produce, pp. 203-260, in Shimshon Ben Yeoshua
(Ed.), Environmentally Friendly Technologies for Agricultural Produce Quality. CRC Press,
Boca Ratón, Florida, USA.
10. PRECOP, 2007. In Spanish “Post-harvest efficiency: generation, development and extension
of suitable technologies to increase the efficiency of conditioning, drying and storing of cereal
grains, oilseeds and industrial crops”. National project of the National Institute of Agricultural
Technologies. INTA PE AEAI5742.
11. SAGPyA, 2007. In Spanish “Monthly agricultural statistics – Official estimations at October
17 of 2007”. Report of the Secretary of Agriculture. Available at: www.sagpya.gov.ar.
Accessed on October 2007.
12. Wilson, D. M. and E. Jay. 1975. Influence of modified atmosphere storage on aflatoxin
production in high moisture corn. Appl. Microbiol. 19: 271.
