Sweet potato

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Code: f54
Latin name: Ipomoea batatas
Source material: Fresh sweet potato
Family: Convolvulaceae
Common names: Sweet Potato, Sweetpotato, Yam, Batata

Allergen Exposure

Geographical distribution
The Sweet potato, belonging to the Morning glory family and not related to Potatoes, is native to the West Indies and Central America, although early reports place it in Indonesia and Philippines too. It is a vine-like, perennial herb but is cultivated as an annual. It is now grown in more than 100 countries in tropical, sub-tropical and temperate climates. It is 1 of only 7 world food crops with an annual production of more than 100 million metric tons per year, and ranks thirteenth globally in production value among agricultural commodities. It is cultivated primarily for the enlarged edible storage roots, which provide large amounts of starch.

Although variation in storage root skin and flesh colour is abundant, there are 2 general types of Sweet potato: a dry, mealy, and a moist, seedy type. In most developing countries, the root has white to cream-coloured flesh and a bland, non-sweet flavor. In contrast, the type most used in developed countries has yellow or deep orange root flesh, a moist texture, a very distinct flavour, and high sugar content. This type is mistakenly referred to as “Yams” in the US, but the true Yam is of the family Dioscorea.


Environment
Sweet potatoes are a staple food of many peoples of the tropics, but in the industrialised world are principally a vegetable or a dessert. They are cooked, canned, frozen, dehydrated, and used as a source of flour, starch, glucose syrup and alcohol. Various products such as candy, pastas, flour, and drinks are produced in local industries. Both the starchy roots and vines can be used as animal feed. Nutrients supplied include vitamin C, iron, potassium, calcium, and fibre. The moist orange-fleshed variety is high in beta-carotene (a precursor of vitamin A).

Sweet potatoes contain trypsin inhibitors, and if eaten raw may reduce the ability to utilise protein. However, trypsin inhibitors do not survive cooking and are of no consequence in cooked roots.

Unexpected exposure
The starch is used commercially for sizing textiles and papers, for the manufacture of adhesives, and in laundries. In the US, large quantities of Sweet potatoes, either freshly harvested or shredded and dried, are used as feed for livestock.

Allergens
No allergens from this plant have yet been characterised.

A beta-amylase has been isolated. It showed 50-60% amino acid sequence identity with beta-amylases from Soybean and Barley, and about 25% with bacterial beta-amylases deduced from cDNA sequences (1). Its allergenic potential has not been evaluated.

Potential cross-reactivity
An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among members of the family Convolvulaceae (2).

Clinical Experience

IgE-mediated reactions
Anecdotal evidence suggests that Sweet potato can occasionally induce symptoms of food allergy in sensitised individuals; however, no studies have been reported to date.

IgE antibodies to Sweet potato have been measured in children (3-4) and in adults (5) using the Pharmacia ImmunoCAP® System. Other species of Ipomea are involved in allergic pollinosis (6).

Other reactions
Sweet potato has been implicated as a cause of infantile food protein-induced enterocolitis syndrome (FPIES), a severe, cell-mediated gastrointestinal food hypersensitivity typically provoked by Cow’s milk or Soy (7).

In a study of subjects with irritable bowel syndrome (IBS), 70 fresh food extracts were applied to the back by the prick-by-prick method. SPT was positive in 17 (38.6%) treated patients, in 5 (16.1%) untreated patients and in 1 (3.3%) control. Three of 44 (17.6) of the treated patients were skin prick test-positive for Sweet potato (8).

Sweet potato may be infected with the mould Fusarium solani, which produces a toxic substance, furanoterpenoid (9).

Compiled by Dr Harris Steinman, harris@zingsolutions.com

References

  1. Toda H, Nitta Y, Asanami S, Kim JP, Sakiyama F. Sweet potato beta-amylase. Primary structure and identification of the active-site glutamyl residue. Eur J Biochem 1993;216(1):25-38
  2. Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
  3. Matsumaru S, Artia M et al. Clinical evaluation of Pharmacia CAP System new allergens for fish, vegetables, fruits and grains. Paper presented at Jap Soc Ped Allergol 1992
  4. Yamada M, Torii S. Clinical evaluation of Pharmacia CAP System new food and inhalant allergens. Paper; Japanese Soc Allergol 1992
     
  5. Konatsu H, Miyagawa K, Ikezawa Z. Study of clinical efficacy of Pharmacia CAP System new allergens in patients with atopic dermatitis. Paper presented at Japanese Soc of Allergology 1992
     
  6. Mondal AK, Parui S, Mandal S. Protein profile of the allergenic pollen of Ipomoea fistulosa L. – comparative study. Ann Agric Environ Med 1998;5:131-4
     
  7. Nowak-Wegrzyn A, Sampson HA, Wood RA, Sicherer SH. Food protein-induced enterocolitis syndrome caused by solid food proteins. Pediatrics 2003;111(4 Pt 1):829-35
     
  8. Jun DW, Lee OY, Yoon HJ, Lee SH, Lee HL, Choi HS, Yoon BC, Lee MH, Lee DH, Cho SH. Food intolerance and skin prick test in treated and untreated irritable bowel syndrome.
    World J Gastroenterol. 2006; 12(15):2382-7
     
  9. Parasakthy K, Shanthi S, Devaraj SN. Lung injury by furanoterpenoids isolated from Fusarium solani infected sweet potato, Ipomea batatas.
    Indian J Exp Biol 1993;31(4):397-8

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.