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Temperature Treatments for Postharvest Dried Fruits and Nuts

Temperature Treatments for Postharvest Dried Fruits and Nuts. Judy Johnson USDA-ARS-SJVASC Parlier, California. Control of postharvest insects is critical to the large and diverse dried fruit and nut industry. Processors rely heavily on chemical fumigants for postharvest insect control.

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Temperature Treatments for Postharvest Dried Fruits and Nuts

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  1. Temperature Treatments for Postharvest Dried Fruits and Nuts Judy Johnson USDA-ARS-SJVASC Parlier, California

  2. Control of postharvest insects is critical to the large and diverse dried fruit and nut industry. Processors rely heavily on chemical fumigants for postharvest insect control. Temperature treatments are potential alternatives.

  3. On-farm fig storage Covered almond piles Yard stacks of raisins Several dried fruit and nut crops are produced in the Central Valley of California, storage methods vary widely, from outdoor storage…

  4. Dried fruit warehouse Walnut silos Almond silos … to warehouse storage and large silos.

  5. Sun-drying natural raisins Walnut dehydrator Drying methods range from sun-drying to mechanical, forced hot air dehydrators… …and cold storage is often used to preserve product quality.

  6. Insects of concern are of two broad types… Direct field pests Stored product pests …regardless, tolerance for live insects at the consumer level is zero.

  7. Navel orangeworm Indianmeal moth The two major insect pests for these products… Most of our research is directed at these two pests.

  8. Our major research effort… Use of low temperatures High temperature radio frequency treatments

  9. Low Temperature • Using temperatures of 0-10C • First object is to prevent infestation • For some life stages, long exposures are needed for disinfestation • Some commodities are routinely stored at low temperatures to maintain quality

  10. 0.4 Eggs 0.3 Developmental Rate (1/days) 0.2 Pupae 0.1 0 10 13 16 19 22 25 28 31 Temperature (°C) Developmental thresholds for Indianmeal moth

  11. Raw, infested product Clean product protected from reinfestation by cold storage Disinfestation (Processing Step or Treatment) Use of Cold Storage in Combination Treatments

  12. Cold storage protection against Indianmeal moth infestation in walnuts, almonds and raisins was tested.

  13. Almonds Walnuts Moths/week Moths/week Weeks Weeks Raisins Moths/week Weeks Indianmeal moth trap results for combination treatments

  14. ? Clean product? Cold storage Potential for reinfestation… Raw product Disinfestation

  15. Adult Indianmeal moth mortality at 10C

  16. Indianmeal moth fertility after 30 day exposure to 10C

  17. LT95 (days) for insect eggs at low temperatures

  18. Larval and pupal survival at 10C

  19. Larval and pupal survival at 5C

  20. Larval and pupal survival at 0C

  21. Low temperature treatments against diapausing Indianmeal moth larvae require sub-freezing treatment temperatures.

  22. Mortality of diapausing IMM larvae at -10C

  23. Mortality of diapausing IMM larvae at -15C

  24. Mortality of diapausing IMM larvae at -20C

  25. High temperature radio frequency treatments • Radio frequency heating provides very rapid heating throughout the product • Product quality is not effected when subjected to high temperatures for short periods • Treatment times as short as 10 minutes are possible

  26. Thermal death points were first determined in heat block studies… …treatments based on this work were tested in radio frequency ovens.

  27. Relative heat tolerance of red flour beetle stages Averages within columns followed by different numbers are significantly different (LSD means separation)

  28. NOW 100 IMM RFB Linear (RFB) Linear (NOW) Linear (IMM) Time (min) 10 0.1 42 44 46 48 50 52 54 Temperature (C) Comparison of TDT curves for target species

  29. Comparison of lethal times (minutes) for target species Target Species Temp (°C) RFB NOW IMM LT 95 48 64.5 40.9 7.6 50 7.9 13.5 2.2 52 1.5 4.3 0.9 LT 99 48 75.4 46.8 8.8 50 9.5 15.3 2.5 52 1.7 5.0 1.0

  30. Fifth instar navel orangeworm was used for tests in radio frequency ovens.

  31. Mortality of fifth-instar NOW in walnuts after radio frequency (27 MHz) treatment to 55°C Treatments consisted of 60 test insects replicated 3 times

  32. Other results from radio frequency studies • Walnut quality is not harmed • May need higher temperatures to disinfest almonds • Addition of hot air becomes more critical with products like almonds

  33. Questions?

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