Nutritional quality of corn stored in plastic bags with different moisture levels

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 practice in the country in recent years is the storage of grains in plastic bags. Under these conditions it is possible to generate a low-oxygen modified atmosphere, rich in carbon dioxide (Azcona et al., 2009) which limits the development of insects and microorganisms and allows storage of grains with moisture levels even above those recommended for traditional storage systems.

Objective

To evaluate the effect of moisture content of corn stored in plastic bags on commercial quality and nutritional value for poultry.

Materials & Methods

To store grain from the same source with different moisture contents, several crops were carried out at different times, including also a control naturally dried in the plant.

Plastic bags of 15 to 20 tons were used with storage times ranging between from 3 to 10 months.

Commercial quality, dry matter, protein, lipids, acidity (AOAC, 1975), mycotoxins (AOAC, 1990) and true metabolizable energy (TME) (Sibbald, 1976) were determined. Finally, growth tests were conducted with Cobb male chickens, housed in cages or floor at a rate of 10 to 16 birds per pen. Each treatment had 6 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 3-stage feeding plan was provided: starter up to 21 days, grower up to 35 days and finisher up to 49 days.

Corn from different bags was air-dried to achieve moisture of control group (14 - 15%) so there would not be differences in dry matter supply and subsequent risks of fungal growth in feed.

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

In 2002, three treatments were compared:

1- Wet material (19%), stored in plastic bag.

2- Wet material (16%), stored in plastic bag.

3- Naturally dried material.

The first control was conducted in August, at 3 and 5 months post-harvest (materials with 16% and 19% moisture, respectively). The second control was conducted in October, at 5 and 7 months post-harvest according to considered moisture level.

In 2003, three treatments were compared:

1- Wet material (19%), stored in conventional plastic bag (20 tons).

2- Wet material (19%), stored in experimental plastic bag (50 to 60 kg).

3- Naturally dried material.

Controls were performed at 4, 6, and 10 months of storage, and the last control in late January 2004, so that the silo was exposed to temperature variations characteristic of each season.

In 2004, two treatments were compared:

1- Wet material (16%), stored in conventional plastic bag (20 tons).

2- Naturally dried material.

Controls were performed at 3 and 10 months of storage.

Results & Discussion

Spoilage of commercial quality associated with moisture contents was observed; test weight was the most affected parameter. Overall, test weight of materials maintained in bags declined from 1 to 2 percentage points. Consequently, continuance of corn in grade 1 depended on the test weight at the time of bagging. Studies with experimental bags (50-60 kg) showed that, despite a demonstrated fall of test weight, weight losses after 10 months of storage were minimal (0.6%). In the case of naturally dried materials, test weight did not change over time, except when samples were evaluated after 10 months of storage where there was a of this variable.

A odd odor was detected (alcohol), particularly in the case of bags with higher moisture, which negatively affected the commercial quality.

There were no changes in the initial and final moisture of silos or the protein and lipids contents. Corn stored under high moisture showed an increase in acidity associated with storage time, of greater magnitude than that observed in naturally dried materials. The increased acidity in the case of materials stored in bags could be the result of lactic fermentation process.

The true metabolizable energy/gross energy ratio (TME/GE) (%) tended to decrease with storage time. This result was also observed in the case of corn preserved in traditional silos and would be a consequence of "aging" of the grain.

Table 1 shows the results obtained in 2002 where, due to the entry of horses to the silos area, some of them broke. No differences between treatments were observed in gross energy content, metabolizable energy and the relationship between the two, except for corn with 19% moisture for the broken silo. In this case, there was an increase in the metabolizable energy content of 146 calories observed, mainly due to increased utilization of gross energy. Under anaerobic conditions, microbial activity could modify the contents of gross energy and/or facilitate the use of it (Azcona & Schang, 1998). In any case, this result does not confer any advantage, on the contrary, this silo should be dismissed since there was a significant spoilage of commercial quality and occurrence of mycotoxins.

Table 1. True metabolizable energy content (dry basis)

Treatment (% Moisture)	Months of Storage	GE (Cal/g)	TME (Cal/g)	TME/GE (%) (%)
19 %	4 (Broken silo)	4588	4294^a	93.6
5 (Good silo)	4557	4180^b	91.7
16 %	3 (Broken silo)	4548	4176^b	91.8
3 (Good silo)	4544	4145^b	91.2
Natural Drying	3	4538	4150^b	91.4
CV%			1.46

^{GE: Gross energy. TME: True metabolizable energy. CV: Coefficient of variation.
Means with different superscripts in a column differ significantly (p<0.05).}

In the case of the broken silo with 16% moisture, data collection continued after repairs, because there were no significant changes in quality.

However, after 5 months of storage, when feed made with corn stored with 16% of moisture from the damaged silo was provided, a slower growth was observed
(-4.2%) and a worse conversion (+0.9%), compared with treatment based on naturally dried corn (Table 2).

Table 2. Production results in 2003 (49 days)

Treatment (% Moisture)	Months of Storage	Live Weight (g)	Diff. (%)	Conversion	Diff. (%)
19 %	7 (Good silo)	2961^a	+3.1	1813	-1.0
16 %	5 (Broken silo)	2751^c	-4.2	1850	+0.9
5 (Good silo)	2908^ab	+1.2	1821	-0.6
Natural Drying	5	2871^b		1832
CV%		2.5		2.0

^{Diff.: Difference (%) compared to natural dried material. CV: Coefficient of variation.
Means with different superscripts in a column differ significantly (p<0.05).}

This response is due to the presence of mycotoxins, which led to lower feed consumption (-3.4%). This time, Aflatoxin B1 (22 ppb) and Fuseranone X (500 ppb) were detected.

However, chickens fed corn stored with 19% moisture and maintained in optimal conditions (good silo), grew 3.1% more than chickens fed naturally dried corn, and had a better feed conversion (-1.0%) . These advantages were of a lesser magnitude in the case of the good silo with 16% moisture (Table 2).

This result could be associated with a mobilization of nutrients caused by the enzymatic activity that takes place in wet conditions, as reported in the case of studies carried out with soaked rye (one part of grain - one part of water) and stored in closed plastic bags during 144 h (Pawlik et al., 1990). This "pre-digestion" would allow a faster use of feed and therefore more consumption, without causing changes in terms of nutrient concentration, such as protein and metabolizable energy.

Table 3 presents a summary of the results corresponding to the seven growth tests carried out between 2002 and 2004. They are expressed as differences (%) compared to the naturally dried material.

Table 3. Summary of production results

Year	Time Storage (Months)	Duration Trial (Days)	Moisture (%)	Body weight Diff. (%)	Conversion Diff. (%)
2002	5	49	16	+1.2	-0.6
7	49	19	+3.1	-1.0
2003	4	49	19	+1.9	-1.6
6	42	19	+3.6	-1.7
10	44	19	-0.8	+2.9
2004	3	35	16	-3.0	+0.4
6	49	16	-1.3	-0.2

^{Diff.: Difference (%) compared to naturally dried material.}

Improvements in growth and conversion observed in 2002 with corn silage with 19% moisture were also repeated in 2003, except when storage time was of 10 months. In the latter case, the silo experienced climatic changes characteristic of spring - summer, a situation that affected the corn nutritional value.

In 2004, results were adverse because mycotoxins were produced in the bag during storage (aflatoxin B1: 28 ppb, citrinin: 20 ppb and fuseranone: 500 ppb) due to cracks in the folds caused by rodents. Consequently, there was less growth, an effect that was of greater magnitude (-3%) when corn stored for 3 months was evaluated, probably due to the fact that trial finished at 35 days and the young birds are more susceptible to mycotoxins. In the study of 6 months of storage, impaired growth, although smaller (-1.3%) was also observed. This time, the trial ended at 49 days so the birds were able to recover and close the gap with respect to the naturally dried grain control group.

Conclusions

A 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 in test weight did not involve a loss of grain weight and did not affect the performance of chickens.
At higher moisture storage, the greater risk of loss of commercial quality and nutritional value, if there are bag broken that allow the formation of mycotoxins.
Corn silage with 19% moisture showed an improvement in the nutritional value and consequently on the growth and conversion of birds when there were no breaks in the bags.
When moisture at storage was of 16%, improvements in production response compared with the naturally dried material were of a lesser magnitude than those achieved with 19%.

References

AOAC. 1975. Official Methods of Analysis. 12th ed. Association of Official Analytical Chemistry, Washington, DC.

AOAC. 1990. Official Methods of Analysis - Method 1184-1205. 15th ed. Association of Official Analytical Chemistry, Washington, DC.

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.

Azcona JO & Schang MJ. 1998. Uso de "EUROMOLD L-PLUS" para la conservación de maíz. Acuerdo INTA - EUROTEC. Pergamino.

Francomano & Picardi. 2011. Producción mundial de maíz 2010/11 - Newsletter semanal. URL:http://www.francomanopicardi.com.ar/news/Produccion-Mundial-de-Maiz.htm. Acceso: 01/Abr/2011.

Pawlik JR, Fengler AI, Marquardt RR. 1990. Improvement of the nutritional value of rye by the partial hydrolysis of the viscous water-soluble pentosans following water-soaking or fungal enzyme treatment. British Poultry Science 31(3):525:538.

Sibbald IR. 1976. A bioassay for true metabolizable energy in feedstuffs. Poult. Sci. 55:303-308.

Snedecor & Cochran. 1967. Statistical Methods, 6th ed. NY.