Postharvest Handling of Tree Nuts and Dried Products
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Transcript of Postharvest Handling of Tree Nuts and Dried Products
Postharvest Handling of Tree Nuts and Dried Products
Jim ThompsonUC Davis
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.
AlmondAlmond
WalnutWalnut
Maturity Stages
Tree Shaker almonds & walnuts
Windrow & Pickup almonds & walnuts
Storage at high temperature and relative humidity
Concealed Damage of Almonds
Pick-up Machine for Walnuts
Walnut Hulling & Drying
Kernel Darkening from Sun Exposure
Price is inversely related to kernel color
Walnut Kernel Color Quality
- Pistachio shell split is desirable.
- Early hull split is not desirable because it increases potential for fungal infection.
Pistachio Maturity
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.
Shake-Catch System for Pistachio Harvest
Sorting Pistachio Nuts to Remove Defects
Pistachio Hull Removal
Shell Staining
Shell Staining Scale for Pistachio Nuts
Pistachio Drying
• Two-stage– Heated-air drying to about 12% moisture– Ambient-air drying to 5-6% moisture
• Heated-air• Sun
Pistachio DryersCross-Flow
Continuous Belt
Drying Temperature
Drying Time to 5 – 6% MC
Open shells – kernels released
(°F) (°C) (h) (%)140 60 14 0160 71 10 1180 82 7 3200 93 5 6
Drying Temperature
Should not exceed 71°C (160°F)
Storage Potential
Storing Nuts & Dried Fruits and Vegetables
• Water activity – maintain the dry chain
• Temperature
• Oxygen concentration
• Effective insect control
• Time
• Cultivar
Water Activity of Selected Nuts and Dried Fruits & Vegetables
Equilibrium Moisture Content
Rockland, 1957
Placentia Perfection walnuts stored for 7 months at 72°F
3
4
5
6
7
8
9
0 20 40 60 80Storage Humidity (%)
Hed
onic
Sca
leOdor
Flavor
TasteLow quality
High quality
Kernel Darkening
0
4
8
12
16
20
0 3 6 9 12Storage Time (mo)
Dar
k Ke
rnel
s (%
)
Pedro
Serr
Lopez et al., 1995
Insects and Decay
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
Aeration to Control Storage Temperature and Humidity
• Regularly ventilate storage with outside air to maintain uniform nut moisture in storage.
Average Air Temperature
M onth
30405060708090
S O N D J F M A M J J A
Sacramento
Red Bluff
Cooling
Tem
pera
ture
30
20
10
0
°F °C
Maintain temperature as long as possible
Grain Aeration Components
Perforated floor
Ventilation fan
Metal grain bins
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.
Sensory Quality of Irradiated Almonds
Quality is reduced at 1.5 kGy or higher
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.
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.