Efficient Drying and Safe Storage of Agricultural Seeds and Products

Elizabeth MitchamUniversity of California, Davis

Director, Horticulture CRSPDirector, 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. BradfordUniversity of California, Davis

Rhino Research, CABI, IDE, CEAPREDHorticulture 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 DesiccantsDesiccants 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

developmentService model could be developed for regeneration of beads for farmers -microenterprise

Dry and Store Seeds using Beads

Roberts EH (1972). Viability of Seeds. Chapman and Hall Ltd., Syracuse, NY, pp 14-58.

Other Storage Problems Are Prevented at Low RH

Pepper Seed Storage in Thailand Before storage After 6 mo storage

Open storedvs

Bead stored

All seeds germinate

Seedlings

Higher seedling vigor

Six months storageWithout beads69% infestation

With beads0% infestation

Storage Insect Control using Drying Beads

Courtesy of Keshavulu Kunusoth, ANGRAU, Hyderabad, India

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

Drying beads: reduction of 58% in 72 h

Other Postharvest ApplicationsDrying of fresh horticultural products

Chili peppers

Drying of Apple and Tomato Slices with Drying BeadsRatio 1:8

Stack Dryer• 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

Cabinet Dryer

Improved Solar Drying

Thank You!!

http//:hortcrsp.ucdavis.edu