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Postharvest Handling of Tree Nuts and Dried Products

Postharvest Handling of Tree Nuts and Dried Products

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Postharvest Handling of Tree Nuts and Dried Products

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  1. Postharvest Handling of Tree Nuts and Dried Products Jim Thompson UC Davis

  2. Handle Chestnuts like Fresh Fruit Rather than Tree Nuts • Store at -1 to 0°C (30 to 32°F). • Cooling promptly to stop decay development and preserve quality. • Storage humidity = 90 – 95%. • Package in microperforated plastic film to minimize water loss.

  3. Maturity Stages Almond Walnut

  4. Tree Shaker almonds & walnuts

  5. Windrow & Pickup almonds & walnuts

  6. Concealed Damage of Almonds Storage at high temperature and relative humidity

  7. Pick-up Machine for Walnuts

  8. Walnut Hulling & Drying

  9. Kernel Darkening from Sun Exposure

  10. Price is inversely related to kernel color Walnut Kernel Color Quality

  11. Pistachio shell split is desirable. • Early hull split is not desirable because it increases potential for fungal infection. Pistachio Maturity

  12. Pistachio Nut Maturity Indices • Ease of hull separation from shell. • Shell dehiscence (splitting). • Change in shell color (green to ivory). • Decrease in fruit removal force. • Kernel dry weight and fat content.

  13. Shake-Catch System for Pistachio Harvest

  14. Sorting Pistachio Nuts to Remove Defects

  15. Pistachio Hull Removal

  16. Shell Staining

  17. Shell Staining Scale for Pistachio Nuts

  18. Pistachio Drying • Two-stage • Heated-air drying to about 12% moisture • Ambient-air drying to 5-6% moisture • Heated-air • Sun

  19. Pistachio Dryers Cross-Flow Continuous Belt

  20. Drying Temperature Should not exceed 71°C (160°F)

  21. Storage Potential

  22. Storing Nuts & Dried Fruits and Vegetables • Water activity – maintain the dry chain • Temperature • Oxygen concentration • Effective insect control • Time • Cultivar

  23. Water Activity of Selected Nuts and Dried Fruits & Vegetables

  24. Equilibrium Moisture Content

  25. Taste 9 Low quality Odor 8 Flavor 7 Hedonic Scale 6 5 4 High quality 3 0 20 40 60 80 Storage Humidity (%) Placentia Perfection walnuts stored for 7 months at 72°F Rockland, 1957

  26. Kernel Darkening 20 16 Serr 12 Dark Kernels (%) 8 Pedro 4 0 0 3 6 9 12 Storage Time (mo) Lopez et al., 1995

  27. Insects and Decay

  28. Insects cause Quality and Weight Loss • Navel orangeworm • Indian meal moth • Dried fruit beetles • Saw tooth grain beetle • Merchant grain beetle • Raisin moth • Fruit fly

  29. Aeration to Control Storage Temperature and Humidity • Regularly ventilate storage with outside air to maintain uniform nut moisture in storage.

  30. 9 0 8 0 R e d B l u f f 7 0 6 0 S a c r a m e n t o 5 0 4 0 3 0 S O N D J F M A M J J A Average Air Temperature °C °F 30 20 10 0 Temperature Maintain temperature as long as possible Cooling M o n t h

  31. Grain Aeration Components Perforated floor Metal grain bins Ventilation fan

  32. Insect Control Procedures • Fumigation - methyl bromide, phosphine, propylene oxide. • Freezing at -18 ºC for more than 2 days. • Heat treatment (50-55 ºC). • Exposure to 100% carbon dioxide for more than 2 days. • Storage temperature <10 ºC reduces insect activity. • Storage in 0.5% oxygen (balance nitrogen) atmosphere reduces insect activity. • Irradiation at 750 Gy.

  33. Sensory Quality of Irradiated Almonds Quality is reduced at 1.5 kGy or higher

  34. Experimental Insect Control Treatments • Fumigation with carbonyl sulfide, sulfuryl fluoride, or ethyl formate. • Controlled atmospheres (<0.5% O2 and/or 40-60% CO2). • Heat treatments (radiofrequency). • UV & IR radiation.

  35. Reduce Losses of Dried Products • Dry below 0.65 water activity. • Store below 10°C (50°F), storage time increases with lower temperatures. • Clean storage before filling. • Protect from birds and rodents. • Insect disinfestation as needed. • Protect against reinfestation using insect-proof packaging.