Dry material losses and qualitative evaluation of corn grain stored in hermetic units / Determinação da perda de matéria seca e avaliação qualitativa de grãos de milho armazenados em bolsas herméticas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

A significant increase in the grain sector has been observed over the last few years, leading to the expansion of the balance of trade. However, in various Brazilian States, storage systems are composed of old structures, precarious for storage which end up compromising the quality of the product during storage. In order for the sector to increase exports and gain credibility on the world market, storage systems should be adapted to international quality standards. These demands have heightened interest in the use of effective pest control techniques with minimal contamination, of which hermetic storage in silos was emphasized and utilization de allyl isothiocyanate (AITC). In the search for information which supports the method for storage in silos, the present work was developed with the objective of estimating the dry material losses and evaluating the utilization of AITC and its possible effect on the preservation of corn grain quality when stored in hermetic units. Corn grain with moisture contents of 14.8% and 17.9% w.b. was added to polyethylene bags, impermeable to gas and submitted to a 300 μL L-1 AITC treatment, each was done in triplicate. AITC was applied on filter paper measuring approximately 5 cm2 and was placed inside the bags containing the grain. After AITC treatment, all excess air was removed and the bags were sealed with a thermal sealing machine. The control sample was processed and stored under the same conditions, however in the absence of AITC. After all bags were closed and sealed, they were stored in temperature controlled chambers at 15, 25, and 35 C. A total of 180 bags were used, including three repetitions for each combination of moisture content, temperature, treatment and storage period. During a 150 day period, three bags corresponding to each moisture content, temperature and treatment were removed from the chambers at 30 day intervals for the measurement of O2 and CO2 concentrations. Afterwards, the corn was submitted to commercial classification, moisture content, apparent specific mass, germination potential and electrical conductivity analyses and later disposed of. To estimate the loss of dry material, a model was developed as a function of the respiratory rate of corn, considering the occurrence of aerobic and anaerobic respiration. From the obtained results, it could be concluded that the consumption of O2, the production of CO2, and consequently the dry material mass were affected by the corns moisture content and temperature. At temperatures of 15, 25 and 35 C, the stored corn with moisture contents of 14.8 and 17.9% maintained dry material losses at levels less than 0.5%, the limit of dry material loss generally used by open storage systems. Due to the low respiratory activity of the corn and the microflora, and the low production of CO2 during the anaerobiosis phase, the increase in dry material loss with time was disregarded. The loss of dry material in stored corn with a moisture content of 17.9% and temperature of 35 C was inferior to the loss verified for corn stored at 25 C. However, by monitoring CO2 concentrations at intervals before 30 days, the results may be inversed for the given conditions. In relation to the quality parameters evaluated, it was verified that for the conditions utilized in this study, the dosage of 300 μL L-1 of AITC did not significantly affect the physiological quality of the corn stored in hermetic bags, inducing the idea that it did not have a controlling effect on the microflora present. Storage in hermetic bags permits the stability of moisture content in the corn during the complete 150 day period, independent of temperature. Storage of corn with moisture contents of 14.8 and 17.9% in hermetic bags at temperatures of 15, 25 and 35 C for a period of 150 days can be achieved without reducing quality standards for commercial usage. Corn grain storage with moisture contents of 14.8% allow for the preservation of its characteristics for greater time periods and with fewer dry material losses than the storage of grains with moisture contents of 17.9%. The typical acceptable limit (0.5%) of dry material loss for corn storage in open systems cannot be applied to hermetic systems. This is because as the grain enters anaerobiosis, its respiration rate decreases and the increment in dry material losses decrease with time to the point where it becomes negligible. So, the dry material loss can be considered maximum before reaching levels of 0.5%, since while the grains continue to deteriorate, quality standards are also reduced as storage time increases. For this reason, it is important for more detailed studies to be done, with more frequent measurements of CO2 concentrations for grains stored with high moisture contents and for long time periods. Limits for dry material loss in hermetic grain storage units should also be established for corn grain.

ASSUNTO(S)

armazenamento de grãos grain storage atmosfera modificada modified atmosphere engenharia de processamento de produtos agricolas hermetic bag silos silo bolsa

ACESSO AO ARTIGO

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