Trace elements in flour and bran from common and tartary buckwheat

Abstract

The contents of Se, Cr, Rb, Zn, Fe, Co, Sb, Ba, Ni, Ag, Hg and Sn were analysed in the flour and bran of common and tartary buckwheat, obtained by milling in a stone mill. In both species most trace elements are concentrated mainly in the bran. However, there are relatively small differences in the contents of iron, antimony, and chromium between flour (extraction rate 55%) and bran fractions. In tartary buckwheat fine flour (extraction rate 42%) there is a lower trace element content than in normal flour. The potential use of buckwheat bran as a dietary source of Zn, and Se, is indicated.

Introduction

Two buckwheat species are used for food: common buckwheat (Fagopyrum esculentum) and tartary buckwheat (Fagopyrum tataricum), the latter being grown in more harsh climatic conditions (Bonafaccia et al., 2003, Lin et al., 1992).

In Slovenia, and in other central European countries, buckwheat has been grown for centuries and is now, alongside spelt wheat (Bonafaccia et al., 2000), one of the most important alternative crops. It is suitable for ecological growing without the use of chemicals, following sustainable agricultural practice by developing and extending environmentally conscious technologies (Kreft, 1989, Vadnal, 2002, Vadnal & Bratusa, 2000). Buckwheat may be used for flour and groats products (Kreft, 1994). Buckwheat pasta and other buckwheat flour products are traditionally popular in Italy, Slovenia and in Asian countries (Kreft & Skrabanja, 2002). Other foods obtained from buckwheat are buckwheat floral honey (Nagai et al., 2001, Paradkar & Irudayaraj, 2002), green buckwheat tea, buckwheat sprouts, and fresh green plant parts used as a vegetable (Kreft, 1995, Park et al., 2000).

Buckwheat is safe for patients with coeliac disease (Skerritt, 1986), but it may contain some antinutritional factors—oversensitivity reactions may be caused in a very few people by ingesting buckwheat and its products or by exposure to buckwheat dust (Wieslander & Norbäck, 2001).

Buckwheat products are known as a dietary source of polyphenols (Kreft et al., 1994, Kreft et al., 1999, Kreft et al., 1996, Nagai et al., 2001, Park et al., 2000, Watanabe, 1998), dietary fibre and resistant starch (Skrabanja et al., 1998, Skrabanja et al., 2001) and proteins with high biological value but relatively low true digestibility (Ikeda & Kishida, 1993, Skrabanja et al., 2000). In experimental animals, buckwheat proteins suppress gallstone formation better than soy protein isolate (Tomotake, 2000). They are connected with retardation of mammary carcinogenesis by lowering serum estradiol, and with suppression of colon carcinogenesis by reducing cell proliferation (Kayashita et al., 1999, Liu et al., 2001).

Common buckwheat is grown in Slovenia and in the Alpine region of Italy (Valtellina and Val Venosta), and is used for many traditional regional food products. Tartary buckwheat was cultivated to some extent in Slovenia and Italy for centuries, but this ceased before the end of the 20th century. The cross border region Islek—which includes northern Luxemburg, the Westeifel (Germany) and the border area of the German-speaking part of Belgium—is at present the only place in Europe where tartary buckwheat is still grown, on approximately 50 ha, for human food. The University of Ljubljana, Slovenia, has carried out a pluriannual research project for the Luxemburgish Ministry of Agriculture, in order to further develop the cultivation and utilization of tartary buckwheat.

A few studies have been reported on the contents of zinc, copper, manganese, boron, aluminium, nickel, molybdenum, cobalt, cadmium, chromium, iron and lead in common buckwheat (Ikeda et al., 1990, Ikeda & Yamashita, 1994, Ikeda et al., 2000, Steadman et al., 2001), but there is little information about the content of other trace elements in common buckwheat. In tartary buckwheat, of the trace elements, only zinc contents was studied (Ikeda & Yamaguchi, 1993). The present work is, as far as we know, the first published report on the contents of the trace elements Se, Cr, Rb, Fe, Co, Sb, Ba, Ni, Ag, Hg and Sn in tartary buckwheat grain, flour and bran.

The purpose of this research was to compare the trace element contents of common and tartary buckwheat and to evaluate the possibility of utilizing products of the two species as a source of dietary trace elements.