Аннотация

Amaranth is a promising raw material for enriching foods with protein, minerals, vitamins, dietary fibre, squalene, and other nutrients. However, its varieties differ significantly in composition and properties. The research included two stages. At first, we studied the composition of eight amaranth varieties grown in a collection nursery of Voronezh State Agrarian University. Their composition was a factor that determined their functional use as an enriching ingredient. We found that amaranth grain of the Universal variety could be best used to increase the biological value of foods, whereas the Universal and Valentina varieties could be recommended as multifunctional ingredients. The addition of enriching ingredients into foods, including breads, often leads to changes in their traditional consumer properties. Therefore, our next step was to study changes in the composition of Universal amaranth during extrusion using IR spectroscopy. Also, we assessed the effect of amaranth extrudate on the baking properties of model wheat flour and extrudate mixtures as the main factor of the product’s consumer properties. The results showed a redistribution of moisture between flour gluten proteins and extrudate dietary fibre. We also established amounts of amaranth extrudate needed to ensure the preservation of crumb appearance and structure close to the traditional ones.

Ключевые слова

Grain, foods, gluten, extrudate, flour, IR-spectra, leaves

ВВЕДЕНИЕ

Improving people’s diet involves enriching foods with a variety of essential nutrients. First of all, these include vitamins, some macro- and microelements, dietary fibre, polyunsaturated fatty acids, and other substances [1–7]. Protein is another important component of a balanced diet [1, 4]. Amaranth is a promising raw material and a rich source of nutrients [8–10]. Numerous studies, both in Russia and abroad, have focused on enriching breads and bakery confectionery products with amaranth [11–24]. However, these developments have not yet been commercialized on a large scale. This confirms the need to continue the search for applications of amaranth and its products in the food industry, especially in the production of staple foods such as breads. Thus, we need to develop a technology based on amaranth – not only its composition depending on variety, but also its functional and technological properties.

Our aim was to assess amaranth as a raw ingredient for breads, based on the study of its composition, as well as its functional and technological properties.

ОБЪЕКТЫ И МЕТОДЫ ИССЛЕДОВАНИЯ

Market research was conducted to identify people’s attitudes to enriching ingredients, taking into account permissible changes in traditional consumer properties of a product determined by changes in its formulation. The sample of 405 respondents was representative of the general population in the region. The statistical error did not exceed 5% at a confidence level of 95%.

The object of study was amaranth grown in a collection nursery of Voronezh State Agrarian University. Geographically, the nursery is located in the forest-steppe zone of the Central Black Earth Region. The experiments were carried out on leached, medium loamy chernozem with medium and high availability of nitrogen, phosphorus, and potassium mobile forms. The humus content was 4.5%, pH 5.4–5.8. Precipitation during a period of temperatures above +10°C reached 250–260 mm. Total active temperatures amounted to 2581°C. The seeding took place in the second half of May.

The study covered the following amaranth varieties bred by Voronezh State Agrarian University and the Federal Research Centre of Vegeculture: Voronezh-36, Voronezh, Imperator, Rubin, Universal, Gigant, Dobrynya, and Valentina.

The composition of amaranth grain and leaf mass was determined at the All-Russian Research Veterinary Institute of Pathology, Pharmacology and Therapy according to the following state standards:
– moisture: State Standard 13586.5-2015^I;
– protein: State Standard 10846-91^II;
– fat: State Standard 29033-91^III;
– cellulose: State Standard 31675-2012^IV;
– total sugar (mono- and disaccharides): State Standard 15113.6-77^V;
– ash: State Standard 27494-2016^VI;
– phosphorus: State Standard 26657-97^VII;
– calcium: State Standard 26570-95^VIII;
– carotene: State Standard 13496.17-95^IX;
– copper and zinc: State Standard 30692-2000^X; and
– iron and manganese: State Standard 32343-2013^XI.

The content of digestible protein was determined by the PDCAAS method, with the degree of digestibility being 75% for amaranth grain protein and 65% for amaranth leaf protein [25, 26].

The quality of flour was determined according to State Standard 9404-88XII (moisture) and State Standard 27839-2013^XIII (gluten quantity and quality).

We used top-grade baking wheat flour with a moisture content of 14.43%, a gluten content of 32%, and gluten quality rated as “satisfactory weak” (gluten deformation index, IDK).

Amaranth grain was subjected to extrusion. The extrudate was obtained from whole low-fat grains of Universal amaranth through an EUM-1 compact laboratory extruder at 110–120ºС. Then it was ground to a particle size of max. 125 μm in a laboratory mill.

The infrared absorption spectra were determined in the range of 400–4000 cm^–1 on a Bruker VERTEX 70 FTIR spectrometer in the reflection mode.

Model mixtures were made of top-grade baking wheat flour and amaranth extrudate. The studies were performed at the Dokuchaev Scientific Research Institute of Agriculture of the Central Chernozem Zone. The data were processed in accordance with State Standard R 51414-99^XIV. The quantity and quality of gluten were determined according to State Standard 27839-2013¹³.

РЕЗУЛЬТАТЫ И ИХ ОБСУЖДЕНИЕ

The comparative characteristics of the amaranth varieties studied are shown in Tables 1, 2.

We found that the composition of amaranth grain differed widely, depending on its variety. The highest content of protein was observed in Universal and Rubin, fat – in Universal and Imperator, mineral substances – in Universal and Valentina. Universal also contained the maximum amount of mono- and disaccharides and digestible protein (Fig. 1). Thus, this variety seemed to have the best composition for being used as an enriching ingredient to increase the biological value of foods, including breads. In addition, this grain is white with a slight yellowish tinge, which makes it suitable for any product, regardless of its intended color.

Another important aim of food fortification is an increase in dietary fibre and minerals. We found that the varieties of Valentina and Dobrynya had the highest cellulose content. Universal and Valentina were also rich in minerals. The results of additional studies of amaranth mineral composition are presented in Table 2.

Calcium and iron are two key minerals that Russian diet has a deficiency of [12]. We found that the varieties of Valentina, Universal, and Dobrynya had the highest calcium content, whereas Voronezh-36 and Universal were rich in iron.

As for other minerals, we found a high content of phosphorus in Universal, copper in Gigant and Universal, zinc in Voronezh, and manganese in Valentina. The content of copper and manganese should be considered as a limiting factor when developing food formulations. It is also noteworthy that Valentina has a dark colour, which may affect the sensory perception of the finished product.

Another form of amaranth use is its leaf mass. After harvesting, amaranth leaves were dried by convection at 30–35°C. This method was used to preserve the maximum amount of biologically active substances.

The comparative characteristics of amaranth leaf mass by variety are given in Tables 3, 4.

Amaranth leaf mass showed significant differences in composition. The highest content of protein and digestible protein (Fig. 2) was found in Rubin and Dobrynya, cellulose – in Universal and Valentina, total sugar – in Universal and Gigant. All the varieties had a low fat content and a high ash content. On the whole, the leaf mass of these varieties can be regarded as a protein ingredient. In addition, it can be used as a source of dietary fibre and mineral substances.

The data presented in Table 4 were used to find effective ways of correcting diets with macro- and microelements by introducing supplements from amaranth leaf mass.

We found that amaranth leaf mass was rich in calcium, especially Voronezh-36 and Imperator. Therefore, amaranth can be classified as a functional food ingredient. Compared to grain, amaranth leaves had a much lower content of iron, copper, zinc, and manganese. Of all the varieties, Valentina showed the highest content of zinc and manganese.

A high carotene content was found in the leaves of Dobrynya and Valentina (Fig. 3). Due to the antioxidant properties of carotenes, the leaves of these varieties can be recommended as enriching supplements.

Thus, the comparative analysis of amaranth composition showed the following results:
– amaranth grain and leaf composition differed significantly, depending on the variety; therefore, when developing formulations for functional or specialised foods, it is important to specify the recommended variety;
– Universal amaranth grain is best suited for improving the biological value of foods with a minimal effect on their color range;
– Valentina and Dobrynya grain, as well as Universal and Valentina leaf mass, can be recommended as a source of dietary fibre; however, the color of amaranth grain and its products should be taken into account;
– Valentina grain, as well as Voronezh-36 and Imperator leaf mass, can be used in foods to increase their calcium content, with an allowable level of manganese being max – 5 mg/day^XV;
– Dobrynya amaranth leaves can be recommended for foods with antioxidant properties; and
– Universal and Valentina varieties can be used as polyfunctional ingredients.

Further studies were conducted with Universal amaranth variety, taking into account its color range and potential uses as an enriching ingredient in breads. To increase digestibility and adjust taste and smell, amaranth grain mass was subjected to extrusion. The extrudate was ground to a particle size of max. 125 μm.

The Universal extrudate is a loose powdery semifinished product with a light cream color, a nutty aroma, and a faint bitterish taste, characteristic of amaranth. It contains 4.76% moisture, 27.51% protein, 4.53% fat, and 3.20% cellulose.

Changes in the fractional composition of amaranth during extrusion were studied by IR spectroscopy (Fig. 4).

Absorption bands were identified in the short-wave (3600–2600 cm^–1) and long-wave (1800–900 cm^–1) spectral regions. The first band was characteristic of C–H stretching vibrations of methyl and methylene fragments at 2923–2933 cm^–1 and 2855 cm^–1, as well as O–H and N–H stretching vibrations at 3280–3300 cm^–1 [22]. In the long-wave region, intense absorption was observed at 1000–1050 cm^–1, with a well pronounced band at 1150 cm^–1, which corresponded to vibrations of the C–O–C ester group in the structure of cellulose [27]. The spectral behaviour of amaranth and amaranth extrudate samples was identical. Comparing the relative heights of the absorption bands for amaranth and amaranth extrudate, we found less intensive vibrations of the carboxyl group (1740 and 1650 cm^–1) and amide bonds (1650 and 1540 cm^–1), as well as a lower height of the “ester band” (1050 cm^–1). This was due to the fact that extrusion causes destructive changes mostly in protein components, rather than in cellulose substances. On the whole, the IR absorption spectra analysis confirmed a partial destruction of amaranth proteins and polysaccharides during extrusion. On the one hand, this suggested a better digestibility of the extrudate compared to grain. On the other hand, this indicated the extrudate’s sorption activity with respect to heavy metal cations due to the preserved native structure in some part of the carbohydrate-based biopolymers.

Thus, the study proved the efficacy of extrusion as a way of preparing amaranth for being used as a food ingredient. The extrudate of Universal amaranth variety was used in further research as a bread enriching ingredient.

One of the problematic issues in food fortification is changes in traditional sensory properties, primarily in products’ appearance, shape, condition, and texture (structure of porosity). Our market research showed that most consumers (80%) were not ready for drastic changes in these characteristics, even when the product had an increased nutritional value and an improved nutrient composition (Fig. 5).

Bread’s shape, crumb, porosity, and other characteristics mainly depend on the baking properties of flour. New grain ingredients usually bring about quantitative and qualitative changes in the proteinproteinase and carbohydrate-amylase flour complex, altering the product’s sensory properties. Therefore, the next stage of our research was to study the baking properties of model mixtures of top-grade wheat flour and amaranth extrudate. The choice of top-grade flour was motivated by a lower standardized amount of gluten and, therefore, a more pronounced effect of raw ingredients on the baking properties of the flour mix. The model mixtures were made of wheat flour and amaranth extrudate in the ratios of 95:5, 90:10, 85:15, 80:20, 75:25, and 70:30.

We studied the effect of amaranth extrudate on the content and elasticity of gluten proteins and, therefore, on their ability to form dough with certain rheological properties (Figs. 6, 7).

We found that an increased amount of amaranth extrudate lowered a gluten content in the model mixture. In addition, it raised the IDK index (gluten quality index). Gluten washed out from the model mixture was less elastic. However, it is noteworthy that the changes in gluten quality did not exceed 7% of the initial IDK value.

More detailed information on the effect of amaranth extrudate on the baking properties of the model mixture was obtained using a valorigraph (Fig. 8).

Table 5 presents flour strength indicators obtained from the analysis of the valorigrams. We found that a higher content of amaranth extrudate in the model mixture raised its water absorption capacity. This can be explained by an increased waterbinding ability of amaranth dietary fibre. Water absorption properties of amaranth extrudate were established in [28].

The increased duration of dough development might be due to the redistribution of water towards amaranth extrudate and the consequent slowing down of gluten swelling. This happened when the amount of amaranth extrudate was up to 15%. With a higher extrudate content, the duration of dough development decreased and almost stabilized. This was probably due to a lower content of gluten proteins in the model mixture (Fig. 6).

The decrease in dough stability appeared to be caused by a lower amount of gluten, since it is gluten that gives dough a three-dimensional structure. Dilution is defined as a difference between the maximum dough consistency achieved during kneading and its consistency at the end of kneading. Excessive mechanical impact weakens dough consistency. A lesser dilution of the dough with a greater amount of wheat flour could probably be explained by the temperature parameters characteristic of water binding by protein substances. Another factor might be a better retention of the hydration shell on the protein globules.

All the model mixtures had similar valorimetric values (Table 5). Depending on the ratio of wheat flour and amaranth extrudate, the deterioration of some characteristics was compensated by the improvement of others. This confirmed a possibility of producing breads from a mix of wheat flour and up to 30% of amaranth extrudate with a crumb structure close to traditional. An extrudate content of up to 15% brought about smaller changes in the crumb shape, appearance, and structure, whereas an amount of up to 30% was more effective in increasing the product’s nutritional value. To establish the optimal amount of amaranth extrudate, we need to study the changes in rheological properties during dough maturation and evaluate the product’s taste, color, and nutritional value.

ВЫВОДЫ

On the whole, the study confirmed the potential of extruded amaranth of the Universal variety as an ingredient that can enrich wheat flour breads with protein and dietary fibre and ensure consumer properties close to traditional.

КОНФЛИКТ ИНТЕРЕСОВ

The authors state that there is no conflict of interest.

БЛАГОДАРНОСТИ

The authors would like to express their deepest gratitude for the research material and facilities to V.I. Turusov, Doctor of Agriculture Sciences, Member of the Russian Academy of Sciences, Director of Dokuchaev Agricultural Research Institute of the Central Black Earth Strip; to L.I. Saratovskiy, Candidate of Agriculture Sciences, patent holder and originator of the Universal cultivar of amaranth; M.S. Gins, Doctor of Biology Sciences, Professor and Corresponding Member of the Russian Academy of Sciences, Head of the Laboratory of Introduction, Physiology, and Biochemistry of the Federal Horticulture Research Center; V.K. Gins, Professor, Doctor of Biology Sciences, Senior Researcher of the Laboratory of Introduction, Physiology, and Biochemistry.

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