Importance of Kemel Structure and Composition for Buckwheat Quality

Transcription

1 Importance of Kemel Structure and Composition for Buckwheat Quality Ivan Kreft Biotechnical Faculty, University of Ljubljana, Ljubljana. Slovenia Abstract Buckwheat quality is discussed. in relation to genetic polymorphism, growing and technological conditions. Particular attention is given to buckwheat kernel structure and composition and their importance for buckwheat milling quality. Different flour fraction are obtained after milling. The chemical composition and constituents of buckwheat kernels are discussed in relation to the nutritional value of buckwheat, to the technological quality and to the typical buckwheat taste. Aspects of buckwheat quality The main aspects of buckwheat quality are: (a) nutritional quality, (b) technological quality for different products ordishes, (c) the desired buckwheat taste. Buckwheat growing areas, where buckwheat. is still an important food source, are Nepal, Bhutan and some other regions in several Asian countries. A high buckwheat yield is particularly important there, but also the nutritional quality and taste of buckwheat products. In some of these regions. buckwheat has remained a poor people's food and is regarded as one lower utilization quality and price than rice. There was formerly a similar situation in Europe. when buckwheat was the commonest food of the poor and when wheat was the predominant food cereal of the rich. However because of the high biological value of the proteins, buckwheat is a very important food of mountain regions in Central Asia where the soil and climate are not suitable for other field crops. Buckwheat is important also because some groups of people from these regions do not consume meat for economic. religious or cultural reasons. The nutritional value of buckwheat could also be of great importance in Europe (especially Denmark, Sweden, Germany) and in Japan for groups of people who eat buckwheat products as an important part of everyday food, such as buckwheat morning cereals in Europe or buckwheat noodles consumed by students and working people in small shops in Japan. often very close to railway stations. In all these cases, both the taste of buckwheat and its nutritional quality are important. The main aspect of buckwheat quality in regard to consumption as a special food in developed countries is the specific buckwheat taste. In Japan. there are many restaurants famous for the very tasty buckwheat dishes. It is also possible to obtain famous buckwheat foods in big cities in Europe in Japanese restaurants from Vienna and Berlin to London, Paris and Lisbon. In Europe traditional buckwheat dishes are also very popular, for example buckwheat pasta in south - eastern France. southern Switzerland. northern Italy, and many different buckwheat flour or groats products in Austria, Slovenia and Croatia. In pancakes (crepes). In western Europe, U. S. A. and Canada. people can buy raw dehulled buckwheat groats or flour, to prepare in their homes traditional buckwheat food. Buckwheat groats (kasl)a) is very popular for such purposes in eastern Europe. 191

2 obtained by dehulling thermally pretreated buckwheat kernels. In all such cases. the typical buckwheat taste is of major importance for quality. Special aspects of buckwheat quality are developed in international trade with buckwheat. Among the characteristics of importance are the "fresh" green color of the dehulled kernels. homogeneity in regard to the size. shape and color of the buckwheat kernels. the absence of fungal infection and ' absence of weed seeds or others admixtures. These aspects are important for buckwheat exporting countries like China. Canada. Brazil. Soviet Union and now also Tasmania. and for buckwheat importing countries. of which the most important is Japan. An international buckwheat quality research program cooperation has been proposed by Ploszynski et al. (1988). Genetic differences in the utwzation value of buckwheat We have not yet found very important genetic differences among buckwheat cultivars or populations in regard to protein content. amino acid composition. starch and crude fiber content., There may theoretically exist also genetically influenced difference in chemical composition of buckwheat. but no major differences have been found to date. and the differences detected could also be partly due to ecological conditions and the technology of buckwheat cultivation. Theoretically mutants could be expected some lacking some substances (for example. photosensitive substances. tanninless mutants. etc.). But such mutants. common in some other plant crops. are not yet known in buckwheat. However. there are some differences between buckwheat varieties. buckwheat cultivars or. populations in regard to the thickness' or percentage of hulls and in regard to the size of kernels. These differences could be important in comparison of diploid and tetraploid buckwheat. Further. there are some differences in utilization value between common buckwheat and tartaric buckwheat. They seem to be connected with a taste affecting greenish. water soluble substance and with the content of the hulls. There are no important differences for example in protein content and in amino acid composition (Javornik at al >. Influence of ecology and all'otechnlcal condltions on buckwheat quality The method of buckwheat cultivation. the availability ofsoil nutrients. temperature. humidity and other ecological conditions certainly affect buckwheat quality. The micro-nutrient composition of buckwheat kernels probably depends on he available microelements in the soil. When the kernels are filled. translocaton of photosynthates to the kernels effects the relative size of the endosperm in the kernel. the proportion of different structures of the kernel and may further influence the relative amount of substance in buckwheat kernel. Details are not yet known of the mechanisms of ecological influence on buckwheat kernel structures. composition and utilization value. However. it is for example known that warm and dry weather are not 'suitable for the technological value of buckwheat: buckwheat grown in a temperate climate has a better utilization value. The main parts of buckwheat kernels are: 192 (a) hulls (husk) (b) testa Kernel structures (c) aleurone layer (d) central (starchy) part of endosperm (e) embryo (including cotyledons)

3 Different parts of,. 'Juckwheat kernel have very different chemical compositions. In the hull. there are many fiber substances. The testa is very rich in tannins (Luthar. pen. comm. >. The aleurone layer is rich in proteins. in the endosperm there is mostly starch and few proteins and the embryo (including cotyledons) is very rich (about 50%> in proteins and crude fibers. Buckwheat kernel structures were studied by Pomeranz and Sachs (1972>. by JAvornik and Kreft (1980) and by De Francisco and Kreft (1989). The composition of different fractions of the buckwheat kernel was studied by Marshall and Pomeranz (1982). Due to ge~ factors or ecological conditions. there are different proportions of the mentioned structures in thekemel. Which may influence the further overall chemical composition of the buckwheat kernel. Buckwheat kernels can be milled in various ways and the flour used in different ways. 'Ibis may result in many different flour and groats fractions with very different content of proteins. minerals. starch. fibres and other substances. Moisture and temperature may cause chemical or physical changes in the kernel. chemical reactions and/or migration of substances among different structures of the kernel. especially migration of soluble substances. So different fractions of flour or 'buckwheat groats prepared in different ways may have very different chemical compositions and so also different nutritional and technological values. ChemIcal eompolitlod of the buckwheat kernel The importance of the chemical composition of buckwheat kernels for the nutritional quality of buckwheat and for human diets were reviewed in papers by Javornik.( Y Buckwheat bas an excellent amino acid composition and biological value of proteins (Eggum. 1980; Javornik ; Eggum et al ; Javomik et al ; Javornik and Kreft, 1984). Buckwheat has a relatively high content of minerals (pomeranz. 1983; Kusano et al., 1983; Ikeda S. et al., 1990, Amarowicz and Fornal. 1987> and vitamins (Sokotv. 1983>. Fibers may have a negative effect on digestibility and the utilization of proteins and on metabolized energy. but are very important in human diets. The fiber content of buckwheat grain. flour and hull and groats was studied by Amarowicz and Fornal (1987>. Enzyme inhibitors in buckwheat and their influence on the utilization value of buckwheat were studied by Ikeda and Kusano (1978). Pokrovskii and Belozerskii (1980). Pokrovskii et ale (1981>. Ikeda and Kusano (1983). Kiyohara and Iwasaki (1985) and Ikeda et ale (1986). Properties of buckwheat starch were studied by Kim et ale (1977), Alekseeva et ale (1979>' Lorenz et ale (1982) and Soral - Smietana et ale (1984), Fornal et ale (1981) studied the influence of hydrothermal processes on starch dispersion and gelatinization. The influence of heating on the functional properties of buckwheat proteins is studied by Ikeda et ale (1991). The content of lipids in buckwheat was reviewed by Soral- Smietana (1984) and Javornik (1986). The influence of tannins on the nutritional value of buckwheat was studied by Javornik et ale (1981) and by Ikeda (1987). Tannins in buckwheat have been recently studied by Luthar (unpublished results). The phenolic substances of hulls and groats of different buckwheat species ware studied by Tahir and Farooq (1985). Qemetson (1976) suggested the use of rutin from natural source such as buckwheat. The rutin content in different parts of buckwheat was studied by Shevchuk (1983) Wender (1946) and Brockmann et Sanders (1950) studied fagopyrism. appearing due to photosensitive substances in buckwheat flowers and hulls. Depending on the milling technology. this 193

4 substance could also be contained in flour if there is any admixture of hulls. The phypersensitivity to buckwheat was studied by Horesh (1972). Yanagihara and Koda (1979) and Yagy et al. (1982). Buckwheat is generally regarded as a food safe for patients suffering from coeliac disease. widely used in such a way with good results. However. it is not yet known whether buckwheat proteins contain absolutely no proteins with amino acid sequences similar to that responsible for difficulties of coeliac patients. In some countries like India and China. young buckwheat plants are consumed as vegetables. Tahir (1989). It is The leaf composition of different buckwheats was studied by Farooq and Technological quality of buckwheat Relatively little knowledge is available about factors affecting the technological value of buckwheat and the typical buckwheat taste (Shiratori. and Nagata. 1986; Ikeda et al 1991). However, what exactly is supposed to be a good buckwheat taste. which substances contribute to it and how it could be analyzed ormeasured. is not yet defined. Among other things, buckwheat is grown for special purposes for top quality restaurants, Japanese restaurants. Conclusion this is a problem when for example in Tasmania for How proteins and amino acids influence the nutritional value of buckwheat is relatively well known. Some knowledge about the importance of starch for certain aspects of the technological value of buckwheat also exists. However, for further improving buckwheat quality by genetic studies and plant breeding and to maintain the value through proper harvesting. storage and technology. parameters of importance for the utilization value of buckwheat should be further defined. A definition and simple and quick determination of relevant substances in buckwheat kemelscould make possible the study of genetic polymorphism of relevant characters and proper selection in buckwheat breeding. Such a definition and determination of further substances connected with the utilization value of buckwheat could also make possible the optimalisation of the technological process and buckwheat products of the highest quality. References Alekseeva. E. S. Kirilenko. S. K Filipchuk. P. A Characteristics of starch from different forms of buckwheat Vestnik Sel'skokhozyaistvennoi Nauki. Moscow. USSR No (FSTA. 11 (11) M ). Amarowicz. 19. and Fornal. L Characteristics of buckwheat grain mineral components and dietary fiber. Fagopyrum 7: 3-6. Brockmann. H. E. W., Sanders. E Fagopyrin. a photodynamic pigment from buckwheat (p. esculentum). Naturwissenschaften. 37: 43. Clemetson. C. A. B Ascorbic acid and diabetes mellitus. Medical Hypothesis. 2: 193. De Francisco. A. and Kreft Morphological studies on the location and size of the buckwheat embryo. Fagopyrum 9: ' Eggum. B. o The protein quality of buckwheat in comparison with the protein sources of plant and animal origin. In: Buckwheat. Symp. Ljubljana. Sept Eggum. B. 0.. Kreft. I.. Javornik. B Chemical composition and protein quality of buckwheat (Fagopyrum esculentum Moench). Qual. Plant Foods Hum. Nutr. 30:

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