Food Technology Information Center

Application of Modified Atmospheres Under Plastic Covers for Prevention of Losses in Stored Grain

Executive Summary The overall accomplishment of this project was the development of environmentally and user-friendly temporary or emergency grain storage facilities without the requirement of chemical pesticides, to be used by farmers organizations, cooperatives, grain processors and other intermediary parties where secure reserve stocks must be maintained yet permanent storage structures are lacking.

The research required evaluation of the applicability of using flexible plastic sheeting developed in Israel for modified atmosphere and gastight storage for paddy and corn stacked in the open in the Philippines. Storage cubes and silos manufactured from heavy duty plastic were used in order to provide an inexpensive solution to short and medium term preservation of dry paddy and corn and intermediate moisture content of paddy. Prevention of serious losses of grain in the stores was thus accomplished without the need for pesticides.

A series of preliminary trials were canried out in Israel with prototype plastic structures. Following this, a series of trials were carried out during the second and third years of the project, in the Philippines with paddy and corn. The Philippine investigations comprised both storage under modified atmospheres (MAS) using carbon dioxide flushing of corn, and biogeneration of MAS using gastight storage of corn and paddy without gas replacement. The phenomenon of moisture migration due to temperature gradients within the grain bulks was studied in Israel.

The field trials were accompanied by laboratory studies on the permeability of the plastic sheeting to gases (Israel), resistance to insect penetration (Israel and the Philippines), and resistance to rodent penetration (Israel).

A preliminary model was proposed to study the interdependent changes in gas concentrations, dynamics of insect population and amounts of grain consumed by the insects. Numerical experiments were run to assess the degree of gastightness of the structure expressed as permeation rate of oxygen through the storage membrane, size of grain mass, volume of the storage structure, number of initial insectslkg of grain, respiration rate of the insect population, birth and death rates of the different species, and the amounts of grain consumed. This model will enable prediction of safe storage periods under the different physical and biological variables described above.

Carbon dioxide treatment proved effective for insect control. In view of the frequent nonavailability of C0₂ in the Philippines, particularly of food-grade, the adoption of C0₂ enriched atmospheres using C0₂ cylinders remains limited. Rodent penetration in field trials confirmed the laboratory findings that heavy duty sealed plastic tarpaulin cubes or heavy duty sealed plastic liners as silos provided an effective barrier to rodents when correctly set-up. Although CPE had lower permeability to gases than PVC it was more susceptible to insect and rodent penetration. In field trials in both Israel and the Philippines with elevated moisture content, moisture migration was observed. Use of agricultural wastes provided insulation from diurnal temperatwe fluctuations and was effective in preventing moisture migration.

The trials show that gastight storage provides an acceptable protection by maintaining the number of live insects below the threshold of economic damage. Weight losses in corn stacks under C0₂ purge were comparable to gastight storage in terms of preventing dry matter loss.

This study shows that gastight storage using enclosed plastic sheeting is a feasible alternative for outdoor safe storage of paddy and corn. In the Philippine climatic conditions the period of safe storage should not exceed four months. Under the Israeli climatic conditions wheat storage can be extended up to 4 years. Gastight storage can preserve the quality of wheat, corn and paddy and minimize insect damage with the added advantage of being flexible and transportable. The technology has strong potential for adoption by farmer organizations and cooperatives, private grain traders and millers in their post harvest operations

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