Distribution of a novel angiotensin I-converting enzyme inhibitory substance (2″-hydroxynicotianamine) in the flour, plant parts, and processed products of buckwheat

2″-Hydroxynicotianamine (HNA) is a recently discovered angiotensin I-converting enzyme inhibitory compound present in buckwheat which displays hypotensive activity. Here, HNA levels in buckwheat flour, plants, and products were quantified to examine the potential functionality of this food. The HNA content of buckwheat flour ranged from 16–28 mg per 100 g dry weight. When the content was evaluated by the milling stage, common buckwheat contained 24.3, 24.1, and 34.1 mg in the inner, middle, and outer layers, respectively, whereas tartary buckwheat contained 16.8, 30.5, and 51.8 mg of HNA, respectively. Comparison of the distribution of HNA within buckwheat plants revealed that HNA was predominantly localised in seeds (buckwheat flour). The residual HNA levels after cooking ranged from 21% to 41% in dried buckwheat noodles. This study clarified that buckwheat flour contains high levels of HNA and is a readily available source of HNA if incorporated into one’s diet, which may help reduce hypertension.