**3. Stability of bioactive components in buckwheat and its products during processing**

It is well known that processing can cause chemical changes in food products. Therefore, it is important to consider the effects on bioactive components in buckwheat. Today, there are several technological processes related to buckwheat, which will be presented below.

#### **3.1 Milling**

Milling is one of the technological processes that is inevitable during the processing of buckwheat into flour. During the processing of buckwheat grains into white flour, the husk and outer layers are separated, which lowers the ratio of fibers, minerals, and polyphenolic components.

Hung and Morita [106] explored the possibility of improving the functionality of buckwheat flour by successively milling buckwheat and they found that in 16

different fractions of flour the content of ferulic acid and rutin increases with an increased ratio of outer grain layers. The same authors found that the antiradical activity on DPPH extracts of free and bound polyphenolic components of buckwheat, the fraction of the successive milling of buckwheat is highest for fractions containing external grain parts. Additionally, better antiradical activity on DPPH was registered for extracts of free polyphenolic components compared to extracts of bound polyphenolic components in buckwheat grain.

Inglett et al. [107] examined the antioxidant activity of ethanolic extracts of four types of commercial buckwheat flour and found the highest antiradical activity on DPPH in buckwheat flour containing a high ratio of husk and aleurone layer, while the lowest antiradical activity was registered in white flour consisting exclusively of the endosperm. The highest content of total polyphenolic components and total flavonoids was registered in whole buckwheat flour. Gallardo et al. [108] established that the content of rutin in buckwheat flour is 0.7 mg/100 g and 11.2 mg/100 g in buckwheat husk.

A recent study found that the buckwheat protein contents decreased from the exterior to the interior parts of the groats [109]. Significantly higher content of amino acids, fatty acids, polyphenols, and flavonoids was found in the bran of Tartary buckwheat, compared to the flour [110].

It should be noted that the milling conditions should be adapted to the type of buckwheat. The granulation composition of common and Tartary buckwheat flour differed under the same milling conditions and affected the physical characteristics of the obtained flour fractions. Tartary buckwheat flour contained larger fractions compared to common buckwheat flour under the same milling conditions [111]. By adjusting the grinding and knowing the content of different components in the fractions of Tartary buckwheat, it is possible to obtain products of different nutritional value [45, 111].

#### **3.2 Heat treatment**

The number of studies researching the effects of heat treatment on buckwheat foods has increased significantly. Today, many new thermal techniques are used in the food industry to improve the quality of functional buckwheat food. The extrusion process has become important in the production of pasta, ready-to-eat cereals, snacks, animal feeds, and textured plant proteins. Microwave heating has gained popularity in food processing due to the ability of this technique to achieve high heating rates, significantly reduce cooking time, provide more uniform heating and safe handling. This technique could change the taste and nutritional properties of food to a lesser extent, as opposed to conventional heating during the cooking process [112]. However, data on the effects of heat treatments on the antioxidant capacity of buckwheat and its products are still limited. In general, most studies are aimed at determining the effect of heat treatment on the content of total phenols and flavonoids due to their role in the management of human health and diseases.

It was established that the heat treatment of buckwheat causes changes in its chemical composition and, above all, that it affects the functional properties of the selected bioactive components. The results published so far on the effects of the heat treatment on buckwheat grain and processed flour are contradictory.

One of the first studies was conducted by Dietrych-Szostak and Oleszek [40] who examined the effect of heat processing on flavonoid content in hulled grains and buckwheat husks by removing the husk using heat. Removing the husk from

#### *The Importance of Buckwheat as a Pseudocereal: Content and Stability of Its Main Bioactive… DOI: http://dx.doi.org/10.5772/intechopen.102570*

buckwheat grain by applying heat treatment resulted in a product that was both visually and chemically different. The peeling process removed primarily the multitude of tannins and crude fibers that are naturally present in the husk. As for the concentration of total flavonoids, dehulling process with different temperature treatments caused a drastic reduction of the total flavonoid concentration in the grain (by 75% of the control) and smaller but significant (15–20%) reduction in the hulls.

Kreft et al. [12] compared the content of rutin in buckwheat products with its content in the raw materials used to obtain these products. Noodles prepared with 70% of integral buckwheat flour contained much less rutin (78 mg/kg DM) compared to the integral buckwheat flour (218 mg/kg DM) out of which they were produced. As a possible explanation for this reduction in rutin content in the product, the authors cited the presence and activity of an enzyme that degrades rutin, flavonol 3-glucosidase, during dough mixing. The presence of this enzyme in buckwheat was confirmed by Suzuki et al. [113]. In raw (uncooked) hulled buckwheat grain (raw buckwheat semolina) the rutin content was 230 mg/kg DM, while in pre-cooked hulled buckwheat grain its content was 88 mg/kg DM. The aforementioned authors explained the established reduction of rutin content in hulled buckwheat grain due to hydrothermal treatment by possible degradation of rutin molecules or its combination with some other molecules, in such a way that it becomes insoluble in the applied solvent. A similar reduction in rutin content was observed during bread production in different combinations of wheat and Tartary buckwheat flour (100:0; 70:30; 50:50; and 0:100) where the effect of making bread and baking on the content of rutin, quercetin, and polyphenols and the antioxidant activity of said loaves was examined. After baking, rutin (0.47 mg/g) was present in bread which is made of 100% Tartary buckwheat flour, together with quercetin (4.83 mg/g). The dough that this bread was made of contained a lower concentration of rutin and greater concentration of quercetin compared to flour used to prepare it; wherein 0.0175 mmol of rutin degraded with the addition of water and yeast to Tartary buckwheat flour, and 0.0149 mmol of quercetin was obtained at the same time. This indicates that 85% of the rutin was converted to quercetin by adding water and yeast to the flour [114].

Degradation of rutin can be the result of activities of the rutin-degrading enzyme found in buckwheat. This enzyme is stable and active at pH 5–7 and below 40°C. Based on the comparison of the level of concentration, it appears that quercetin is more stable compared to rutin in the process of proofing and baking bread. There were no significant differences in the content of rutin and quercetin between the bread crumb and crust. Additionally, the results showed a reduction in the total polyphenol content in all samples of bread as a result of the heat treatment in the baking process [112].

The obtained results were consistent with the results of the authors Alvarez-Jubete et al. [21] which showed a significant decrease in the concentration of total polyphenols, particularly phenolic acids in bread made of common buckwheat flour (0.65 mg GAE/g) compared to the concentrations of these components in buckwheat grain (3.23 mg GAE/g). During the process of mixing and proofing the bread, there was a modest increase in the concentration of total polyphenols in bread samples made with 100% wheat flour and 100% Tartary buckwheat flour, and a slight reduction in the other samples, containing a combination of both kinds of flour (70:30 and 50:50).

Reductions in polyphenol content and antioxidant activity were also reported during baking of bread samples prepared in different combinations (90:10; 80:20; and 70:30) of rice and buckwheat flour (wholemeal and white) relative to their content in flours. It was noticed that the baking process resulted in a higher percentage

of reduction in total polyphenols in bread samples made white buckwheat flour, while only minor or insignificant changes were observed in lower percentages (10 and 20%) in samples with wholemeal buckwheat flour, and only the sample with 30% of wholemeal buckwheat flour had a decrease of about 17%. In addition, the decrease in antioxidant activity was more pronounced in bread samples prepared with white buckwheat flour. During baking, there was a loss in rutin content in bread samples relative to its assumed (calculated) content, and this loss increased with increasing the proportion of buckwheat flour, both types (wholemeal and white), in the range of 4.57–40.4%. The opposite trend was observed in the quercetin content, which increased from 1.5 to 7 times, probably due to the hydrolysis of rutin into quercetin [115].

Similar results were shown in bread samples produced with the addition of buckwheat in the amount of 15 g/100 g and 30 g/100 g. A decrease in the content of total phenols, total flavonoids, and antioxidant activity in bread samples relative to their content in flour was found. The content of total flavonoids in bread samples was 2 to 4 times lower compared to its content in flour [116].

The thermal treatment of Tartary buckwheat bran and flour significantly reduced the content of fatty acids, polysaccharides, and polyphenols. As for the content of amino acids and total flavonoids, their content in bran after heat treatment decreased, while increased in the flour of Tartary buckwheat [110].

In addition to bread and cakes, a decrease in the content of bioactive components was observed in the production and cooking of other products with the addition of buckwheat such as spaghetti, pasta, noodles, etc. A decrease in the content of free (about 74.5%) and bound (about 80%) phenolic components "farm to table", i.e., from flour to cooked spaghetti with buckwheat was found. Regarding the content of total phenolic components, the spaghetti production process (mixing, extrusion, and drying) caused a loss of 45.9%, which the authors explain by the increase in temperature during the extrusion process and the high temperature (about 95°C) reached during drying. Further degradation of phenolic components was found after cooking spaghetti. The boiling process caused the degradation of 52.9% of the total phenolic components. This degradation was significantly different (p < 0.05) compared to post-production degradation. This effect can be attributed to the solubility of phenolic components in boiled water. Of the total phenolic components that were present in the spaghetti after the drying process, 11.6% were dissolved in water after cooking [117].

Biney and Beta [118] also reported that the production and cooking process led to a reduction in phenol content and antioxidant activity in spaghetti enriched with buckwheat flour and bran. The production process did not cause statistically (p < 0.05) significant changes in the content of total phenols between flour mixtures and uncooked products. However, cooking significantly reduced total phenols in all spaghetti samples. Although the addition of buckwheat flour resulted in a significantly higher content of these components in all spaghetti samples, the average percentage of decrease in total cooking phenols due to cooking was higher in samples containing buckwheat flour or bran, compared to control samples prepared from semolina. The production and cooking process also led to a significant reduction in the content of rutin and total flavonoids in spaghetti samples. The higher the proportion of buckwheat in the spaghetti formulation, the greater the losses in rutin content.

The results of similar research (pasta enriched with buckwheat flour in the amount of 20%) showed a reduction of about 44% of total phenolic components after cooking compared to their content in pasta after drying; 8.37% of total phenols

#### *The Importance of Buckwheat as a Pseudocereal: Content and Stability of Its Main Bioactive… DOI: http://dx.doi.org/10.5772/intechopen.102570*

from dried pasta was present in the water in which it was boiled, and 35.63% was degraded. The cooking process reduced the rutin content by about 8.50%. During cooking, rutin was converted from its bound form to quercetin, which is shown in the increase of quercetin content by about 20%. The results also showed that catechin showed a minimum tolerance to the cooking process, with a loss of about 57% [119].

Furthermore, the autoclaving of buckwheat grains caused a decrease in free and an increase in bound phenolic forms in flour. Similarly, this was found in noodles produced by adding this flour to the formulation with wheat flour, compared to the content of these components in noodles produced in the same way with flour obtained from untreated buckwheat grains. Although autoclaving caused an initial reduction in rutin in treated grain flours, it prevented further degradation and conversion of rutin to quercetin in uncooked and cooked samples obtained from these flours, causing a possible improvement in the sensory acceptability of noodles. The loss of phenolic components in noodle samples with added buckwheat flour during cooking (48.1–61.1%) was at the same level as in the control sample with wheat flour only, indicating that buckwheat-containing pasta can maintain the quality during cooking [120].

Cho and Lee [121] examined the thermal stability of rutin in wheat instant fried noodles fortified with rutin-enriched material (REM) from buckwheat milling fractions. The noodles were fried at different temperatures (150, 170, and 190°C) during different periods of time (1, 2, and 3 minutes). Also, noodles were placed in boiling water at different periods (0, 3, and 6 minutes) to examine the effect of cooking on rutin content. The results showed that different temperatures and frying times did not negatively affect the rutin content, while a marked loss of rutin was observed after cooking the noodles.

However, the results of another study showed a reduction in bioactive components in buckwheat products during various heat treatment processes and reported an increase in the total antioxidant activity in buckwheat sprouts and shoots after autoclaving treatment. Furthermore, an increase of 20% and a reduction of 7% of total phenols were observed in buckwheat sprouts and shoot respectively [122].

Contradictory results were also found by Zieliński et al. [123] during extrusion of buckwheat, which showed a decrease in antioxidant capacity accompanied by a reduction in rutin and isovitexin, but at the same time an increase in free phenolic acids and those freed from ester bonds. The authors stated that the reported increase in phenolic acids could be due to the increased release of these bioactive components from the matrix, making them available for extraction. The same authors report that, although the extrusion caused a marked reduction in antioxidant content in hulled buckwheat grain, the amount of bioactive component in hulled buckwheat grain after thermal treatment was still significant, resulting in a decrease in antioxidant activity of only 10%.

Hes et al. [124] also reported contradictory results when testing the impact of cooking in water on the antioxidant properties and dietary fiber of hulled buckwheat grain. It was shown that cooking in water for 30 minutes in a ratio of 2:1 (water: grain) has no negative effects on the nutritional characteristics of the hulled buckwheat grain. Extracts of cooked hulled grain showed a significantly higher content of polyphenols and total dietary fiber compared to raw grain. The detected higher content of polyphenols in cooked hulled grain is explained by the authors as a result of their partial release from the bound form of the protein as a result of cooking. Additionally, phenols can also be associated with other components such as carbohydrates. In terms of individual phenolic components, a significantly higher content

of catechin particularly stands out, and, in contrast to that, a considerably lower content of p-coumaric acid in the extracts of cooked buckwheat grain compared to the extracts of the raw buckwheat grain. Cooking did not cause any changes in rutin content.

It has been recognized that the possible beneficial effects of phytochemicals present in buckwheat may be related to the inherent antioxidant capacity of these components. Therefore, during the last decade, the relationship between antioxidant capacity and these components after heat treatment has been exposed. The antioxidant capacity of buckwheat products is linked to flavonoid concentrations after hydrothermal treatment [125]. Kreft et al. [12] described significant correlations between rutin content and antioxidant activity of buckwheat grain and buckwheat food products. Chlopicka et al. [116] found positive and significant correlations between total phenols and antioxidant activity in buckwheat bread samples, as well as between total phenols and antioxidant activity of buckwheat bread samples, and, finally, between antioxidant activities themselves. Zhang et al. [126] reported that the baking, heating under steam pressure, and microwave heating of integral buckwheat flour had a statistically significant (P < 0.05) effect on the decrease in total flavonoids and antioxidant activity of flour, while the decrease in total phenols in buckwheat flour was less pronounced for all three applied treatments. As a possible explanation, the authors cited the creation of Maillard reaction products, which react with Folin-Ciocalteu reagent, resulting in masking the actual decrease in polyphenol content.

Similar conclusions regarding the formation of Maillard reaction products were reached by the authors Constantini et al. [127] during the production of bread with the addition of Tartary buckwheat flour, where a loss in the total antioxidant capacity and content of total polyphenols and flavonoids was observed, relative to their values in flour mixtures. The aforementioned authors pointed out that it is possible that the real reduction is greater than what was found in this study. As an explanation, they stated that heat treatment of cereals and pseudocereals, such as during baking, can also result in the synthesis of substances with antioxidant properties, including certain products of the Maillard reaction that occur in the crust of bread. These syntheses can mask the actual decrease in the content of total phenols and flavonoids (which are able to react with Folin-Ciocalteu reagent), as well as any loss in total antioxidant capacity.

Aside from phenols, other components, such as proteins, appear to be involved in the formation of the antioxidant activity of buckwheat products. The frying hulled buckwheat grain, in addition to reducing antioxidant activity, also resulted in a decrease in protein content and quality, while heat treatment did not show an effect on whole grain proteins [125]. In addition, during thermal treatment, Maillard components are generated due to a chemical reaction between the free amino groups of lysine and the carbonyl groups of reducing sugars [128]. It was observed the formation of Maillard products was caused by heat treatment of both whole and hulled buckwheat grains. Although Maillard components may be harmful to health, they may contribute to an increase in antioxidant activity, masking the actual decrease in total phenolic components, as highlighted in the above studies [125–127]. In addition, it has been suggested that antioxidant capacity may increase as a result of dissociation (separation) of phenolic forms and release of phenols bound to cell walls due to heat treatment followed by polymerization/oxidation of phenolic constituents or by-product generation [122].

The influence of baking on the content of tocopherols in buckwheat bread was investigated. Vitamin E loss was found to be about 30%. Smaller losses were observed *The Importance of Buckwheat as a Pseudocereal: Content and Stability of Its Main Bioactive… DOI: http://dx.doi.org/10.5772/intechopen.102570*

in bread samples of 100% buckwheat flour compared to samples in which the share of buckwheat flour was 50% [81]. A significant reduction in vitamin E content (about 63%) in buckwheat was also found during the extrusion process [123].

The importance of common and Tartary buckwheat is generally recognized. However, one should also keep in mind some disadvantages of their application in the bakery in terms of sensory impression. This primarily refers to the particle size and the proportion of bran that can negatively affect the rheological properties of the dough and result in an inappropriate texture of bakery products. In addition, the finished products with Tatary buckwheat may appear a slightly bitter taste [6].

Based on all of the above, it is indicative that the contradictory results obtained so far greatly emphasize the importance of determining the exact composition and ratio of bioactive components. In addition, more studies are needed to identify the effect of heat treatment on the functional components, including proteins and phenolic components, of buckwheat products, in order to ultimately obtain buckwheat of consumption quality. Therefore, processing conditions, such as time and temperature, need to be optimized to preserve the functionality of bioactive components.

#### **3.3 High pressure**

High pressure has been shown to be a viable alternative to heat treatment, with no adverse effects such as forming an off flavor, loss of vitamins and phytochemical properties, and discoloration [129]. The effect of high hydrostatic pressure treatment (200 MPa at 2, 4, and 9 minutes) on total antioxidant capacity (TAC), reducing capacity (RC), and rutin content of raw and roasted buckwheat groats were examined. After high-pressure treatment, the content of TAC and rutin differed in the case of raw and fried semolina. The TAC of raw and fried semolina subjected to high-pressure treatment was 16–20% and 12.5–17% lower, respectively, compared to the TAC of untreated semolina. Hydrophilic antioxidants were the main components contributing to the TAC of raw and fried semolina subjected to high-pressure treatment. RC decreased in the case of raw buckwheat (raw semolina), while the rutin content dropped in a shorter time compared to fried semolina. In contrast, overpressure in fried semolina increased the RC formed by hydrophilic antioxidants by 18% when measured by cyclic voltammetry on average and decreased the concentration of rutin after treatment [130].

The results of Zhou et al. [131] suggested that treatment under high pressure at 45 °C improves the nutritional properties of buckwheat compared to untreated and treated under high pressure at room temperature.

#### **3.4 Ionization and radiation**

Radiation is a method of treating food to make it safer to eat and to extend its shelf life. Traditionally, this process is used to control surface microorganisms on vegetables and fruits without affecting nutritional quality. Hayashi et al. [132] reduced the microbial load to a lower level by exposing buckwheat grains to softelectrons without affecting their quality. Chun and Song [133] conducted a study in which aqueous chlorine dioxide, fumaric acid, modified packaging atmosphere enriched with CO2, and ultraviolet radiation (UV) were combined in the treatment of buckwheat sprouts to improve microbiological quality. A decrease in total aerobic bacteria, yeasts and moulds, and enterobacteria to low levels was observed without affecting sensory quality. However, after the treatment, there was an increase in the

concentration of rutin. A comparative study by Orsák et al. [134] studied the effects of UV, microwave, and γ-radiation on three buckwheat samples. Different effects were observed depending on the radiation system and the applied dose on the content of polyphenols and rutin. In addition, it has been described that the content of rutin and flavone C-glycosides is improved in sprouts after exposure to LED (light-emitting diodes) [135].

Therefore, radiation could be offered as a way to increase the half-life of food, maintain sensory quality, improve microbiological quality and increase nutritional value due to bioactive components in buckwheat products. Although public knowledge about radiation remains limited, interest in buying "safe—radiation-enhanced food" is increasing, especially after obtaining information about the potential benefits and risks.
