Consumption and contact with common buckwheat have been reported to cause allergic reactions, including skin eruptions, asthma, and even anaphylaxis. Little has been reported about allergies to tartary buckwheat; however, a protein has been purified from that species that is very similar to the allergen purified from common buckwheat.
Allergy to common buckwheat occurs both in countries where the species is a significant component of the diet, and in countries where it is not. Besides being a food allergy, common buckwheat has been associated with asthma or skin eruptions in workers in noodle shops and health food businesses. Moreover, nocturnal asthma has been observed in some Korean children sleeping on pillows stuffed with buckwheat hulls. Rare cases of anaphylaxis have also been reported, as have cross-reactivity with rice, poppy seed, latex, cashew, walnut and sesame (Sammut et al., 2011).
In a sample of 90,000 Japanese schoolchildren, 0.22 percent exhibited allergic reaction to common buckwheat (Wieslander and Norback, 2001). In Shanxi province, China, reactions to buckwheat were tested in small samples from three exposed groups: agricultural researchers (N=16), noodle makers (N=25), and patients consuming it as a functional food (N= 20). Weekly consumption of buckwheat was reported by 34 percent of respondents, and weekly consumption of tartary buckwheat by 23 percent. Only one (asymptomatic) subject exhibited a positive skin prick test; one reported a history of asthma; four reported a history of allergic rhinitis (Wieslander at al., 2000).
The reaction to common buckwheat protein is mediated by Immunoglobulin E. In seeds of common buckwheat, a 24 kDa globular protein (BW24KD) is the most frequently reactive allergen, but proteins of nine, 16, and 19 kDa are also suspected to play a role. Wang et al. (2004) purified protein from tartary buckwheat seeds and tested fractions (20 to 90 kDa) for reactivity with IgE. When tested against sera from two individuals allergic to buckwheat, the purified 24 kDa fraction was highly reactive. In contrast, the sera of five patients with allergies to other plants displayed only slight binding activity to tartary buckwheat proteins, the latter ranging in weight from 40 to 55 kDa. The authors reported that the tartary buckwheat 24 kDa protein was stable when exposed to 100ºC for at least 20 minutes (but less than 60 minutes).
In 2006, Wang and co-authors cloned a cDNA of the allergenic 24 kDa tartary buckwheat protein, which they had named “TBa.” They sequenced an open reading frame (ORF) of 588 nucleotides, and a 3’-terminal sequence of 180 nucleotides (Genbank accession AY044918). The ORF was 95 percent homologous with the allergenic storage protein from common buckwheat, and 93 percent homologous with a legumin-like protein from the same species. (Legumin is a water-soluble albuminous storage protein found in seeds of several leguminous and non-leguminous plant species. ) Refolded recombinant TBa exhibited specific binding activity with IgE antibody in the sera of a patient with a history of buckwheat allergy, similar to the reactivity of the allergen extracted from tartary buckwheat seeds.