Ensuring performance of hermetic bag storage technology for food security and resource sustainability
Date
2023-05
Authors
Ignacio, Ma. Cristine Concepcion Dungca
Major Professor
Advisor
Maier, Dirk E
Bern, Carl J
Bowers, Erin L
Rosentrater, Kurt A
Vorst, Keith L
Committee Member
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Abstract
Hermetic storage is an innovative technology commercially available to reduce post-harvest losses and improve food security of smallholder farmers and the rural poor. It can effectively control insect activity in stored grains, oilseeds, and pulses without pesticides, thus preserving them biologically. In support of increased adoption of this technology, this research addressed remaining challenges to understand the factors influencing effectiveness in achieving and maintaining a low-oxygen environment, and efficacy in preserving quality and quantity of stored products.
The first study focused on identifying and quantifying the fundamental mechanical and barrier properties of hermetic bag liners as a basis for establishing an American Society of Agricultural and Biological Engineers (ASABE) engineering standard for testing and rating their hermeticity. Six commercially available hermetic storage bag liners (AgroZ®, Elite, PICS™, GrainPro, Storezo, Zerofly®) were evaluated for tensile, impact, tear, and penetration resistance and oxygen transmission rate (OTR) and water-vapor transmission rate (WVTR) following American Society for Testing and Materials (ASTM) test methods. Results indicate significant differences (p-value< 0.05) in material properties among brands.
The second study aimed at estimating the environmental and economic impacts of hermetic storage bags as a sustainable technology. Liners were analyzed for structure and polymer composition using Confocal and Raman microscopy that confirmed categorization into low (AgroZ®, GrainPro, Storezo, Zerofly®) and high (Elite, PICS™) OTR gas barrier types. Life cycle assessment (LCA) from cradle-to-grave showed that bag manufacturing contributes most to environmental impact, i.e., 84.6% to 90.8%. Carbon footprint contribution for total service delivered per hermetic bag ranged from 1.1 to 1.7 kg CO2 eq. Economic benefits of using hermetic bags resulted in highest profit and storage loss reduction when used for three years compared to traditional methods.
In the third study, a storage experiment was conducted to quantify effectiveness of hermetic bag storage technology in achieving and maintaining a low-oxygen environment. Two commercial bag products (AgroZ® and PICS™) were used to store maize with two initial insect infestations for 45 days. After populations were established, a biological (caged maize weevil, S. zeamais) and a chemical (O2frepak®, USA) oxygen scrubber were added for 105 days to evaluate efficacy in reducing oxygen content to lethal levels while maintaining grain quality. After 150 days of storage, hermetic bag liners were tested for gas barrier and mechanical properties following ASTM standard methods. Results indicate that storing maize at < 14% MC w.b. in both types of hermetic bags with 2 zeamais/kg grain initial infestation achieved oxygen concentration below 5% and 8-10% in 105 days after the biological oxygen scrubber and chemical oxygen scrubber were added, respectively. The study found that there were significant (p-value< 0.05) reductions in barrier (OTR, WVTR) and mechanical (elongation, tear strength, penetration resistance, impact failure weight) properties of the two gas barrier liner types after 150 days of storage treatment.
A fourth study developed a model that predicts oxygen depletion in hermetic storage bags as a function of insect and grain kernel respiration, and liner OTR. Results confirmed that insect respiration dominates oxygen depletion in maize stored at safe storage moisture contents of 13-14% while grain respiration is negligible. Bags with low OTR liners reduced oxygen below 5% to asphyxiate adult insects in maize (13-15% MC w.b.) 2 to 14 days faster than bags with high OTR liners at low initial infestation levels (2 adult S. zeamais/kg) stored at 27-33°C. Moreover, high initial insect infestation (10 adult S. zeamais/kg) reduced oxygen levels inside bags in less than 30 days regardless of OTR value of a gas barrier liner.
The fifth study used engineering properties, economic benefits and environmental impacts from the previous studies to rank six commercially available hermetic bag liners using the analytical hierarchy process (AHP). The analysis ranked Storezo bag highest among the six hermetic bags having a global priority value of 0.19 because of its high-performance values for barrier and mechanical properties and carbon footprint. Elite bag ranked lowest because of its low performance values for OTR, dart impact failure weight, and tear strength performance among all six hermetic bags.
This research is the first to quantify the engineering properties of gas barrier liners and to utilize these properties to estimate environmental impacts and economic benefits of commercially available hermetic storage bags. Moreover, this research developed on-line tools that will allow users to quantify effects of gas barrier liner OTR, initial insect infestation level, moisture content, and storage temperature on the performance of hermetic bag storage technology in achieving and maintaining a low oxygen environment, and in preserving quality and quantity of stored products.
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dissertation