Postharvest Handling of Tree Nuts and Dried Products

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.