Nutritional quality of corn stored in plastic bags under a shade screen

Introduction

World corn production for 2010/2011 is estimated at 814 million tons (Francomano & Picardi, 2011). Argentina is characterized as a producer and primarily as an exporter of corn, since the capacity for grain storage and conditioning is a relatively important limiting factor. A widespread local practice is the storage of grain in plastic bags. This generates a modified atmosphere as a consequence of the action of biotic members that consume oxygen and produce carbon dioxide (Azcona et al., 2009). With this storage system, it is possible to have the grain at the site where it was harvested and solve space problems at the point of collection. Furthermore, compared with traditional systems, due to the modified medium that is generated, it is feasible to limit the development of insects and microorganisms, but summer temperatures can affect the nutritional value of grains.

Objective

To evaluate the effect of "shade cloth" coverage on the commercial quality and nutritional value of corn stored in plastic bags.

Materials & Methods

Corn was harvested with 14% moisture and stored in plastic bags for 10 months. A bag remained unprotected while the other bag was covered with plastic known as "shade cloth" capable of retaining 80% of sunlight. A small sample was retained in regular bags, representing the conventional storage system.

Commercial quality, dry matter, protein, lipids, acidity (AOAC, 1975), mycotoxins (AOAC, 1990) and true metabolizable energy (TME) (Sibbald, 1976) were determined on the materials with and without protection and on conventionally stored material. Finally a growth test was carried out to compare the material with and without protection vs. the unprotected stored material. Cobb male chicks were used, which were housed in batteries at 10 birds per lot. Each treatment had 5 replicates distributed in a completely randomized design. Weight and consumption were monitored on a weekly basis in each lot and feed conversion was calculated. A 2-stage feeding plan was provided: starter up to 21 days and grower up to 35 days (Table 1).

Results were evaluated by analysis of variance and Duncan test to separate means (Snedecor & Cochran, 1967).

Table 1. Composition of experimental diets

Ingredients (%)	1 - 21 days	22 - 35 days
Corn	51.408	53,.833
Deactivated soybeans	20.000	20.000
Soybean meal 45	21.303	18.435
Meat meal	5.402	4.633
Shell	0.526	0.653
Oil	0.503	1.732
Methionine	0.309	0.214
Salt	0.200	0.200
Premix	0.200	0.200
Coccidiostat	0.050	0.050
Choline	0.050	0.050
Lysine	0.049
Nutrients (%)
TME (kcal / kg)	3350	3450
Protein	23.00	21.50
Methionine + Cystine (Total - Dig.)	1.02-0.94	0.89-0.81
Lysine (Total - Dig.)	1.30-1.17	1.17-1.05
Threonine (Total - Dig.)	0.87-0.76	0.82-0.71
Calcium	0.95	0.90
Available phosphorus	0.45	0.40

Results

Table 2 shows the results with respect to commercial quality parameters.

Table 2. Effect of coverage on the quality of corn preserved in a plastic bag

Parameters	Treatments
No Coverage	With coverage	Conventional Storage
Test Weight	74.0	75.2	77.2
Damaged kernels (%)	5.3	5.1	11.4
Acidity (eoa)	12.6	14.2	9.2

^{eoa: equivalent oleic acid.}

Corn stored without coverage had a loss of test weight of nearly three points compared to natural dry material, so from the standpoint of commercial quality, it went from Grade 1 to Grade 2. The use of a "shade cloth" cover reduced the of test weight, which maintained the material within Grade 1 after 10 months of storage at 14 - 15% moisture. The percentage of damaged kernels was lower in corn stored in plastic bags compared to conventional storage control, probably because there was no insect damage, while the acidity of bagged materials (with and without coverage) was higher.

Table 3 shows the results of metabolizable energy.

Table 3. Effect of coverage on the metabolizable energy of corn preserved in a plastic bag

Parameters	Treatments
No Coverage	With coverage	Conventional storage	CV (%)
GE (kcal/kg)	4465	4454	4447
TME (kcal / kg)	4104	4148	4149	1,6
TME/GE (%)	91.9^B	93.6^A	93.3^A	1,6

^{Conventional storage: Conventional Storage, GE: Gross energy, TME: True metabolizable energy. Results expressed on a dry basis. Means with different superscripts in a row differ significantly (p<0.10).}

The TME/GE (%) ratio was similar in corn preserved with coverage (93.6%) and in conventionally stored control (93.3%), however, such ratio in bagged corn without coverage was lower (91.9%).

Table 4 shows the production results.

Table 4. Effect of coverage of corn preserved in a plastic bag on the production response of broilers

Parameters	Treatments
No Coverage	With coverage	CV%
Consumption (g)	2523^b	2632^a	1.0
Weight (g)	1716^b	1785^a	2.2
Conversion	1.469	1.474	1.4

^{Means with different superscripts in a row differ significantly (p<0,05).}

Broilers that received bagged corn with coverage showed a significant increase in the feed consumption. Thus, they grew 6% more than chickens fed with bagged corn with no coverage, without differences observed in conversion between the two treatments. This response could be associated with an improvement in nutrient digestibility by adding "shade cloth", which favored the increase in feed consumption.

Conclusions

A reduction of test weight of corn stored in a plastic bag was observed, which could affect the commercial quality, depending on the initial test weight. This effect on test weight was of lesser magnitude when incorporating "shade cloth", which reduces the risk of affecting the commercial quality.
Corn stored with 14% moisture and protected with "shade cloth" for 10 months showed higher nutritional value than their counterparts without coverage, showing a better utilization of gross energy and better growth of chickens.

References

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Azcona JO, Bartosik R, Cardoso L, Casini C, Couretot A et al. 2009. Almacenamiento de granos en bolsas plásticas. Resultados de Investigación. Casini C, Rodriguez JC, Bartosik R (Eds) Ediciones INTA. 180pp.

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