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Vegetables Produce Facts English
Sweet Potato
Recommendations for Maintaining Postharvest Quality
Department of Plant Sciences, University of California, Davis
Maturity & Quality
General Information The sweet potato (Ipomoea batatas) is a warm season root crop. Moist, sweet flesh types of sweetpotatoes are sometimes called "yams", but these should not be confused with true yams (Dioscorea sp.). Cultivars with high orange-colored flesh contain much higher levels of carotenoids than less pigmented types. Sweet potato flavor 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. Good quality sweet potatoes should be smooth and firm, with uniform shape and size, be free from mechanical damage, and have a uniform peel color typical of the variety. There are four U.S. Grades for sweet potato (U.S. Extra No. 1, U.S. No.1, U.S. commercial and U.S. No. 2), and 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.
Temperature & Controlled Atmosphere
Optimum Temperature 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 (55°F to 59°F) 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 (59°F) 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. Roots are not washed before storing in bins or crates, but only after removal for selection and packing for marketing. Sweet potato roots are commonly stored in evaporatively cooled rooms, supplemented by mechanical refrigeration late in the storage period when warm ambient temperatures occur. >95% for long-term storage; 70-90% for short-term handling for marketing
To calculate heat production multiply mL CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day. Sweet potato roots produce very low amounts of ethylene (~0.1 µL/kg·hr), although much higher rates can occur after chilling, wounding and decay development. Exposure to ethylene (1 to 10 ppm) increases respiration rates and phenolic metabolism and adversely affects flavor and color of cooked roots. There is no commercial use of controlled atmospheres for sweet potato storage. Respiration rates of roots are reduced as oxygen is lowered from 21 to 3%. Oxygen concentrations below 3% may results in increased respiration rates due to fermentative metabolism. Response of roots to increased carbon dioxide levels is not known.
Disorders
Physiological and Physical Disorders Disorders Photos
Title: Botryodiplodia Rot Photo Credit: Don Edwards, UC Davis 
Title: Chilling Injury (2) Photo Credit: Leonard Morris, UC Davis 
Title: Fusarium Rot Photo Credit: Don Edwards, UC Davis 
Title: Genotypic Difference in Chilling Injury (1) Photo Credit: Leonard Morris, UC Davis 
Title: Rhizopus Rot (1) Photo Credit: Don Edwards, UC Davis 
Title: Rhizopus Rot (2) Photo Credit: Don Edwards, UC Davis 
Title: Surface Abrasions Photo Credit: Marita Cantwell, UC Davis
Date
August 2001 |
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Use of Materials
The UC Postharvest Technology Center grants users permission to download textual pages (including PDF files) from this World Wide Web site for personal use or to reproduce them for educational purposes, but credit lines and copyright notices within the pages must not be removed or modified.
Except for these specified uses, no part of the textual materials available on the UC Postharvest Technology Center Web site may be copied, downloaded, stored in a retrieval system, further transmitted or otherwise reproduced, stored, disseminated, transferred or used, in any form or by any means, except as permitted herein or with the University of California's prior written agreement. Request permission from UC Postharvest Technology Center. Distribution for commercial purposes is prohibited.
The information in this fact sheet represents our best understanding of the current state of knowledge at the time of the latest update, and does not represent an exhaustive review of all research results. Links to any of these UC Postharvest Technology Center pages are permitted, but no endorsement of the linking site or products mentioned in the linking page is intended or implied by such a link.
How to Cite
Author(s) names. Initial publication or update date (located at the top). Title. Link to the specific Produce Fact Sheet webpage (Accessed date)
Example: Cantwell, M. and T. Suslow. 2002. Lettuce, Crisphead: Recommendations for Maintaining Postharvest Quality.
http://ucanr.edu/sites/Postharvest_Technology_Center_/Commodity_Resources/Fact_Sheets/Datastores/Vegetables_English/?uid=19&ds=799 (Accessed January 18, 2014).
