Sweetpotatoes

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Infobox on Sweetpotatoes
Example of Sweetpotatoes
Sweetpotatoes.jpg
Freshness facts
Optimum carrying temperature +12,5°C/+15C°C
Highest freezing point -1,9°C
Acceptable product temp. at loading into containers Max. 2°C above carrying temperature
Optimum humidity 85% to 90%
Ventilation setting for containers 10 m³/hr
Storage life 6-10 months
Climacteric / non-climacteric Non-climacteric
Ethylene production Very low
Ethylene sensitivity Low
Modified / controlled atmosphere See text
Potential benefits See text
Availability
On demand

Harvesting and Handling

The sweet potato is a warm season root crop. Moist, sweet flesh types of sweet potatoes are sometimes called "yams", but these should not be confused with true yams (Dioscorea sp.). Cultivars with high orange-coloured flesh contain much higher levels of carotenoids than less pigmented types. Sweet potato flavour is largely based on starch and sugar concentrations, and these are affected by cultivars and storage conditions.

Sweet potatoes are harvested when roots have reached the desirable size. Irrigation is typically stopped 2 to 3 weeks before harvest so that vines begin drying before they are removed and roots are harvested. Roots should be cured immediately after harvest at approx. 30°C and 90% to 95% RH for 4 to 7 days, with adequate ventilation. Curing heals wounds from harvest and handling, helping reduce moisture loss during storage and decrease the potential for microbial decay.

Good quality sweet potatoes should be smooth and firm, with uniform shape and size, be free from mechanical damage, and have a uniform peel colour typical of the variety. Quality grades are based on degree of freedom from defects (dirt, roots, cuts, bruises, growth cracks, decay, insects, and diseases), but also size and weight categories.

Cooling and Storage

The recommended conditions for commercial storage are to keep roots cool and dry. Sweet potato roots are chilling sensitive and should be stored between 12,5°C and 15°C with high relative humidity (>90%). A storage life of 6-10 months can be expected under these conditions, although sprouting may begin to occur after about 6 months depending on cultivar. Temperatures above 15°C lead to more rapid sprouting and weight loss. Careful handling during harvesting will minimize mechanical damage to the skin and reduce decay incidence during storage.

Sweet potato roots freeze at -1,9°C and are very sensitive to chilling injury at temperatures of <12°C. The severity of chilling injury depends on the temperature and length of exposure below 12°C. Symptoms of chilling injury include root shrivelling, surface pitting, abnormal wound periderm formation, fungal decay, internal tissue browning, and hardcore formation.

Controlled atmosphere considerations

There is no commercial use of controlled atmospheres for sweetpotato storage. Respiration rates of roots are reduced as oxygen is lowered from 21 to 3%. Oxygen concentrations below 3% may result in increased respiration rates due to fermentative metabolism. Response of roots to increased carbon dioxide levels is not known.

Storage disorders

Bacterial soft rot, Black rot, Chilling injury, Fusarium, Watery soft rot.