Properties of pseudocereals, selected specialty cereals and legumes for food processing with special attention to gluten-free products / Verarbeitungseigenschaften von Pseudogetreide, ausgewählten Spezialitätengetreide und Leguminosen mit speziellem Fokuss auf glutenfreie Produkte

Cereal-based foods form the basis of human nutrition world-wide. Their main task is the supply of nutrition energy as they are rich in high polymer carbohydrates, mainly starch. Besides, cereals can and do contribute a significant amount of biologically active constituents that promote beneficial physiological effects like dietary fiber and their fractions, vitamins and polyphenols, to name only a few. There is a large variety of cereal species that has been and could be used for human nutrition, as well as starch-rich seeds that can be used like cereals, the co-called pseudocereals. Yet today, the production and consumption of cereal species and other starch-rich plants is dominated by only three species, namely wheat, rice and maize (FAOSTAT, 2016). This tendency cannot be seen positively for many obvious reasons, in particular, as appropriate alternatives are available. Alternative or specialty cereal species, pseudocereals and other starch-rich plants show great potential for the development of new food products. First of all, their good nutritional composition in comparison to the named major cereals has to be pointed out. Major cereals have undergone many centuries of breeding. The aim of these breeding programs have mainly been the increase in yield or disease resistance. Regarding the composition and nutritional quality, the focus has been and continues to be on the major components protein and starch, and less attention is paid to the secondary substances such as dietary fiber, polyphenols, phytate or ash. These latter mentioned components were even targets of reduction or elimination, because of adverse effects on quality when present in too high amounts. Only recently, it has been recognized that in a respective dose they can promote human health (decrease chronic diseases, etc.). Specialty cereals show differences in nutritional composition, in dietary fiber fractions, in polyphenols, as well as in mineral, vitamin, protein and amino acid composition. Often they have a high level of these functional components (Abdel-Aal and Wood, 2004).

The non-major cereal species are categorized under various terms: minor cereals, underutilized species, and alternative or specialty cereals (Abdel-Aal and Wood, 2004). While the first two names refer to their low production and consumption amount, the last one gives these species credit for their nutritional importance. Throughout this work, the term specialty cereals has been used.

The pseudocereals amaranth and quinoa were one of the major crops for the Pre-Colombian cultures in Latin-America, but the consumption and cultivation was suppressed after the Spanish conquest. In the mid 1990s, their good nutritional properties were recognized again, in particular their suitability for gluten-free food products. Thus, their production has increased again. The origin of buckwheat is middle Asia. In the 13^th century, it was transferred by nomadic people to middle Europe (Germany, Austria, Italy). Due to the importance of major cereals, its cultivation was decreased in the course of time, but like amaranth and quinoa, it is gluten-free and thus, receives increased attention again.

From a nutritional viewpoint, legumes are an important food source, but their consumption has declined immensely in the last few decades (most likely due to increased meat consumption). While in humans, nutrition like cereals and pseudocereals play a key role in providing energy due to the high amounts of starch in them; legumes are estimated in particular to have high amounts of proteins. Nutrition reports show that Austrians consume legumes only once in two months (Elmadfa et al., 2008). By developing palatable products enriched with legumes, the trend of decreasing consumption of legumes could be stopped. For consumers, easy-to-prepare or even ready-to-eat products (high degree of convenience) would be the simplest way to increase the consumption of legumes again.

In Table 1, the botanical classification of cereals is shown. All cereal species belong to the family Poaceae (Gramineae) and are monocotyledonous. Within each genus, there are a large number of species, for example the colored and pigmented varieties like blue, purple or black wheat, barley or maize varieties, but these are only grown in small amounts. Within major cereal, there is a strong tendency to grow only a few species on the industrial scaled farms. Little used Triticum species are einkorn wheat (T. monococcumL.), emmer (T. dicoccum SCHRANK) spelt wheat (T. aestivum subsp. SpeltaL.), khorasan wheat (“Kamut®„, T. turanicum JAKUBZ) and triticale (X Triticosecale Wittmack). Wheat and rye are also often referred to as bread cereals, as the leavened bread can be produced only from these two major cereals.

Besides these “true” cereals, there is another group of plants that produces starch-rich grains, which can be used like cereals Botanically, they are assigned to the dicotyledonous plants and according to most researchers, they are summarized under the term pseudocereals. Although there are several plants under this group, only three have gained some importance, namely amaranth, quinoa (see Figure 1) and buckwheat. In Table 2, their botanical classification is presented. According to several phylogenetic classifications, the Amaranthus and Chenopodium genus belong together to the Caryophyllales, whereas buckwheat (Fagopyrum) belongs to the Polygonales. Polygonales and Caryphyllales are closely related and are combined together in Caryophyllidae. However, the data obtained by Drzewiecki et al. (2003) indicate the occurrence of significant genetic distance between Polygonales and Caryphyllales, and have been confirmed by Gorinstein et al. (2005). It seems that quinoa, buckwheat and amaranth (as a genus) can be considered as phylogenetic distant taxa, although according to Aphalo et al. (2004) the polymerized 11S amaranth globulin (Globulin-P) presented cross-reactivity with quinoa globulins, and to a lesser extent with globulins of sunflower and rice. Worldwide more than 60 species of amaranth exist. The main grain amaranth species used today are Amaranthus caudatus L. (syn. Edulis Spegazzini), Amaranthus cruentus L. (syn. Paniculatus L.) and Amaranthus hypochondriacus L. Among quinoa, sweet and bitter varieties exist, which is dependent on the content of saponins; that is if the saponin content is below 0.11%, the variety is considered as being a sweet variety (Koziol, 1991). Amaranth seeds are lentil-shaped and measure about 1 mm in diameter. The thousand kernel weight is only 0.51.4 g. Quinoa seeds are slightly bigger than amaranth; the thousand kernel weight is approximately 1.9-4.3 g. In contrast to cereals, the embryo surrounds the starch-rich tissue (perisperm) in the form of a ring and makes about 25% of the total seed weight.

Two varieties of buckwheat are commonly cultivated: common buckwheat (Fagopyrum esculentum) and Tartary buckwheat (Fagopyrum tataricum). The buckwheat seed is a three-angled achene, 6-9 mm long. The fruit of F. tataricum is smaller (4-5 mm) and more rounded at the edges. The thousand kernel weight (10-20 g) depends mainly on the hull thickness. Structurally and chemically, the endosperm resembles that of a cereal grain consisting of a nonstarchy aleurone layer and large cells packed with starch granules constituting the majority of the endosperm.

Legumes belong to the botanical family Fabaceae or Leguminosae, commonly known as the legume, pea, or bean family. They are a large and economically important family of flowering plants. The group is the third-largest land plant family, with about 730 genera and over 19400 species. The most important ones are beans (Phaesolus sp., Vicia sp.), peas (Pisum sp.), chickpeas (Cicer arietinum L.), cow peas (Vigna unguiculata), lentils (Lens sp.) and lupines (Lupinus sp.).

The FAO Statistic Division gives production data for all major and some minor cereals species, as well as pulses (legumes) (FAOSTAT, 2016). In Table 3, the production data of cereals in the year 2014 (latest available data by FAOSTAT, 2016) is summarized, Table 4 shows the production data for pulses. The data for cereals demonstrate clearly the dominance of the three major cereals maize, wheat and rice; these are all produced in amounts higher than 7 billion tons worldwide. Together they make 89.02% of the total cereal production. Compared to these three cereal species, barley is of much less importance but still more than 144 mt are produced (5% of total cereal production), most of which is used for the brewing industry. Thus, barley is also considered as one of the major cereals, although it is hardly used in the baking industry anymore. As described before, apart from these major cereal species, there are many more cereal species that are used for human nutrition, but they are only used in small amounts. All these species together make only 10.98% of the total cereal production. Besides the named major cereals, the FAO Statistic Division lists the following additional species: sorghum, millet, fonio, canary seed, oat, triticale, rye, buckwheat and quinoa. Amaranth, as being another important specialty cereal, is not listed; thus, no production data are available. Additionally, there is no detailed information on the used species, so from these statistics it cannot be estimated in what amounts are the specialty cereals grown within the major cereals (e.g., colored or pigmented wheat, barley, maize species, einkorn wheat, emmer or spelt wheat).

Within the legume species, beans are the most produced leguminous species in the world, followed by chickpeas and peas (FAOSTAT, 2016). Beans are an important crop in Latin America, where its consumption has a long tradition. The combination of maize and beans was the basis of nutrition since many centuries and in some countries, this tradition has remained (e.g., Mexico). Chickpeas are an important crop in parts of Asia and the Mediterranean region of Europe and Africa and are used in the preparation of a variety of snacks (Annapure et al., 1998).

The chemical composition of any grown plant raw material is influenced by species or genotype, growing environment and cultural conditions (e.g., fertilization, soil, etc.). This makes the comparison of various cereal species difficult. Another fact is that there are different analytical methods to determine the composition, which lead to different results. This is in particular true for the determination of dietary fiber. Determination of dietary fiber is at present much discussed and the available methods result in highly different values. Considering these facts, caution has to be taken to compare data from literature. In Table 5, the average values have been collected for gross chemical composition of selected cereal species. Table 6 summarizes these data for selected legumes. For an overview, most data were derived from the food and nutrition tables of Souci et al. (2008; 2013), who collect data from literature and try to consider the methods applied for the determination of relevant constituent. In their original tables, they give the range of data found, as well as the average value. In this work, only the average value was taken. For dietary fiber, the applied method was mentioned in a footnote to the table. Missing data were complemented by additional data from own measurements (where marked).

The most abundant constituents found in cereals are carbohydrates in the form of starch and proteins. Differences between the species exist. Rice, millet and sorghum contain higher amounts of starch, while oat, amaranth and quinoa have lower amounts than wheat, maize, barley or rye. Spelt wheat, amaranth and quinoa show the highest content of protein; the fat content is highest in amaranth, oat and quinoa. The nutritional value of pseudocereals is mainly connected to their protein content. While alcohol-soluble prolamins represent the major storage proteins in cereals such as wheat or maize, the storage proteins of dicotyledonous plants are mainly globulins and albumins (Gorinstein et al., 2002; Drzewiecki et al., 2003). The amino acids composition in pseudocereals is excellent, with a high content of essential amino acids. In particular, methionine, lysine, arginine, tryptophan and sulphur-containing amino acids are found in higher amounts than in other cereals (Matuz et al., 2000; Gorinstein et al., 2002). Immunological studies have shown that amaranth and quinoa do not contain toxic proteins to coeliac disease patients and can thus be used within a gluten-free diet (Hibi et al., 2003; Bergamo et al., 2011). Relevant for health promoting benefits within cereals are in particular dietary fiber and its compounds (e.g., resistant starch, crude fiber, ß-glucan), polyphenols and some vitamins (e.g., folic acid). As here again different analytical methods are applied, it is difficult to compare data from the literature, also some of these data are not available or have a limited availability for specialty cereals or pseudocereals. Our own studies have been conducted to perform some of these analyses, applying the same method for the selected cereals. In comparison to cereal species, amaranth and quinoa contain a very high amount of folic acid (Schoenlechner et al., 2010).

Legumes contain about 20-30% protein. Its amino acid composition complements well with the one of cereals. The proteins of legumes are rich in lysine and deficient in sulphur containing amino acids, whereas cereal proteins are deficient in lysine, but have adequate amounts of sulphur amino acids (Eggum and Beame, 1983). The combination of grain and legume proteins thus provides better overall essential amino acid balance. Another advantage of legumes is their usually low content of fat (0.6-5.5% in peas, about 1% in beans) and high content of minerals, trace elements and vitamins, in particular of B-group vitamins. The low glycaemic index, as well as the content of phytochemical substances, are the additional positive properties of legumes. The present oligosaccharides raffinose, stachyose and verbascose are connected to flatulence. By fermentation, germination or in lower amount also by soaking these oligosaccharides can be decreased. Their total removal is not advantageous, because these oligosaccharides also act as prebiotics.

In order to increase the range of used cereals and legumes for human consumption, appropriate food products have to be supplied to the consumers. As described above, all these cereal and pseudocereal varieties offer certain nutritional benefits; in particular, the pseudocereals have to be pointed out in this respect. For the production of gluten-free foods, they are of specific interest. Principally specialty cereals can be used for all food processes, but they often require certain adaptation of the recipe or processing conditions, in particular, when they are used as the sole cereal ingredient. Einkorn wheat for example has low gluten strength and rheological properties and thus, the resulting breads show decreased bread volume and crumb elasticity. Grausgruber et al. (2008) demonstrated that the application of individual enzymes and/or emulsifiers or their application in mixtures could significantly improve bread volume and crumb firmness of whole-grain einkorn breads. Special attention has to be paid to sensory properties of the food products developed from these rather unknown cereal varieties, as only highly palatable products will be accepted by the consumers. The taste of amaranth and quinoa is different from the common consumed cereal products. Popping or roasting the seeds prior to milling was shown to improve their palatability. To overcome these challenges, often cereals and pseudocereals are used in flour blends with wheat, which usually requires only minimum process adaption. A lot of research has been performed in this direction. Already a replacement of 10-20% wheat flour by these cereals or pseudocereals was shown to increase the nutritional properties of the resulting end-product and sometimes they were even preferred in sensory evolutions.

With respect to processing, one of the reasons why legumes are consumed in very low amounts today is that the preparation of legumes is time consuming, for example chickpeas need about 2 hours for cooking. Soaking in cold water overnight can decrease cooking time, but care has to be taken to avoid microbial growth. Thus, the supply of already prepared legume products could help to increase its food use, for example precooked legumes. Although tinned products are not usually seen as a healthy option, today steam cooked beans or chickpeas can be found in the supermarket that are not only ready-to-heat, but also have an increased nutritional value and taste (see Figure 2). Another possibility to process legumes is to blend them with cereal flours in conventional products. Studies have shown that by the use of legumes, the sensory properties of final products are not adversely affected, sometimes texture can even be improved. In a study on cookies from wheat or gluten-free flours with chickpea, it was found that chickpea addition decreased the lightness in white wheat cookies while increasing it in whole wheat and amaranth cookies. It significantly increased yellowness in all the cookies. The spread factor of the glutenfree cookies was reduced by chickpea addition and the hardness was increased in white wheat and buckwheat cookies, and decreased in the whole wheat and amaranth cookies. Sensory evaluation demonstrated that chickpea addition increased the acceptability of all cookies, in particular of the gluten-free cookies. Optimal levels of chickpea addition were 20-40% in wheat cookies and 60-80% for amaranth and buckwheat cookies (Yamsaengsung et al., 2012). While the consumption and use of whole legumes is low in many Western countries, legumes are often used to obtain protein concentrates or isolates from plant origin. These are widely applied in the food industry, namely for texture improvement in bakery or dairy products, or as a major ingredient in meat substitute products.

In conclusion, although specialty cereals, pseudocereals and legumes offer nutritional advantages, food products from these raw materials are still rarely offered. Research has demonstrated that these varieties are suitable for valueadded food products. Emphasis has to be laid on efforts to develop and produce sensory appealing food products, in order to encourage the consumption of a wider range of food products again.