Impact of Postharvest Drying and Storage Technologies on Quality of Seeds

Abstract

Seeds are vulnerable to loss of germination and vigor as well as insect and fugal attack during storage. High seed moisture contents (SMC) accelerates seed deterioration, so maintenance of seed dryness through hermetic packaging (The Dry Chain) may prevent these storage losses. Sun dried seeds of maize, wheat, quinoa, cotton, rice and okra were stored in traditional porous storage bags (paper, woven polypropylene, jute and cloth) and hermetic plastic bags (Super Bags) for 18 months. Seed storage in hermetic bag maintained high seed germination by preserving high starch, protein, total soluble sugar contents and α-amylase activity and low reducing sugars, seed leachate’s electrical conductivity (EC) and malondialdehyde (MDA) contents in all crop seeds. In second experiment, seeds were dried to 8, 10, 12 and 14% initial seed moisture content (SMC) and were stored in traditional and hermetic bags for 18 months. Seed storage in Super Bag at 8 and 10% initial SMC maintained low seed moisture and higher germination. Moreover, starch, protein, total soluble sugars and α-amylase activity were higher while EC, reducing sugars and MDA contents were low for the seeds stored in Super bag at 8 and 10% initial SMC. Seed moisture adsorption isotherms were also developed for seeds stored in various bags by incubating the seeds at four different levels of RH (60, 70, 80 and 90%) and a nearly straight lines moisture adsorption isotherms were found for all seeds stored in Super bag with a slight increase in seed moisture at higher levels of RH (80 and 90%) while in rest all traditional bags seed moisture increased with increasing RH. In another study, insect and fugal activities and seed deterioration were monitored in maize and wheat seeds stored at 8, 10, 12 and 14% initial SMC by introducing 30 larvae of Khapra beetle (Trogoderma granarium) and 30 adults of lesser grain borer (Rhizopertha dominica) separately into each type of bag. Insect populations were lower in both maize and wheat seeds stored in Super Bags at 8 and 10% SMC, while seeds stored in all other storage bags had very high insect populations irrespective of the initial SMC. Seed storage in Super Bags at 8 and 10% SMC also maintained seed germination percentages and starch and crude protein contents. Malondialdehydes, aflatoxins B1 and G2 were present at higher amounts in seeds at 14% SMC in Super Bags and in all traditional storage bags, while seeds stored in Super Bags at 8 and 10% SMC had lower values of these compounds. In conclusion, insect populations, storage losses and deterioration of seed quality with respect to germination, loss of food reserves and increased aflatoxin contamination were highly related to seed moisture contents. Maintaining the Dry Chain through hermetic storage of seeds in Super bag at 8 and 10% SMC resulted in better storage of crop seeds.