Efficient Drying and Safe Storage of Agricultural Seeds and Products

Elizabeth Mitcham University of California, Davis Director, Horticulture CRSP Director, Postharvest Technology Center

Seed Quality Is Essential for Agricultural Productivity

Two key components of seed quality: • Improved varieties • High viability and germination capacity – Produce high quality seed – Store seeds with minimal loss of viability until needed

Zeolite Drying Beads for the Seed Industry

Peetambar Dahal and Kent J. Bradford University of California, Davis Rhino Research, CABI, IDE, CEAPRED Horticulture CRSP Novel seed drying beads based on zeolites (molecular sieves) make it feasible to efficiently dry and store seeds at low RH.

High Relative Humidity Shortens Seed Storage Life

Seeds are very sensitive to the ambient relative humidity (RH) of the air. Seed storage life is dramatically reduced at high relative humidity.

Humid Conditions in Tropical Regions Cause Rapid Loss of Seed Viability

Ambient conditions in tropical regions often exceed 75% RH and 30°C during the monsoon season following seed harvest, resulting in rapid seed deterioration in open storage.

Traditional Drying Methods Cannot Reduce Seed Moisture Sufficiently under Humid Conditions

Seeds equilibrate with air humidity. Air drying cannot reduce seed moisture content to safe storage levels in humid climates.

Alternative: Drying with Desiccants

Desiccants can be used to absorb moisture from seeds. Current desiccants have drawbacks that have prevented their widespread use for seed drying and storage. Novel seed drying beads based on zeolites (molecular sieves) make it feasible to efficiently dry and store seeds at low RH.

Advantages of Desiccant Drying Beads

• • • • Drying Beads can dry seeds to a specific and low MC at ambient temperatures in moisture-proof containers Dry seeds inside moisture-proof containers are also protected from molds, insects and rodents Seed quality is preserved for several years No need for cold storage to maintain seed viability – Even for seed banks

Costs of Zeolite Desiccant Beads

• • • • • • 0.3-0.5 beads to seeds ratio for one-step drying $10 to $20 per kilogram – 100kg seed = 30 kg beads = $300 investment Less beads needed if initial drying by air first Dries to low moisture content within few days Beads can be regenerated by heating to high temperatures up to 10,000 times Moisture-proof container needed

Regeneration of Drying Beads

• • • • Various ways to achieve high temperatures needed for regeneration of beads Electric oven Microwave Wood fire and other energy sources Simple device under development Service model could be developed for regeneration of beads for farmers microenterprise

Dry and Store Seeds using Beads

Other Storage Problems Are Prevented at Low RH

Roberts EH (1972).

Viability of Seeds. Chapman and Hall Ltd., Syracuse, NY, pp 14-58.

Pepper Seed Storage in Thailand

Before storage After 6 mo storage Seedlings All seeds germinate Open stored vs Bead stored Higher seedling vigor

Storage Insect Control using Drying Beads Six months storage

Without beads 69% infestation With beads 0% infestation

Courtesy of Keshavulu Kunusoth, ANGRAU, Hyderabad, India

Other Postharvest Applications

Drying of fresh horticultural products

Open-air drying: reduction of 17% in 72 h Drying beads: reduction of 58% in 72 h

Chili peppers

Drying of Apple and Tomato Slices with Drying Beads Ratio 1:8

Improved Solar Drying

• • • • • • • • 2 meter stack to increase air flow Build on earthen berm to maintain heat in evening Air flow concentrated around drying product Cheaper to build than standard cabinet dryer Holds more product Dried sliced tomatoes in less than half the time (2 days) Finalist in international competition for drying breadfruit Could be used for drying many products, including grains and seed

Stack Dryer Cabinet Dryer

Thank You!!

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