Introduction

People have broadened their horizons in relation to food, focusing especially on the health aspects of their food. In recent years, more attention has been paid to the development and production of whole-grain foods to satisfy the food’s diverse nutritional and health needs [1-3]. Whole-grain foods help control cholesterol levels, weight, and blood pressure, as well as lower the risk of diabetes and heart disease. This makes them a good choice for a nutritious diet [4-7].

Wheat flour is the most popular and versatile flour, and contains about 75 percent of the wheat grain. Wheat flour proteins are mainly composed of gliadin and glutenin, which, in the presence of water, increase in volume and become colloidal, forming a bound, elastic mass called gluten [8]. The quality of wheat flour is characterized by its content of mineral substances and certain baking properties. This relationship between the degree of extraction and the content of mineral substances is given by the uneven distribution in the grain of wheat, with the center of the grain being less present and the outer part, the content, becoming more and more abundant [9, 10]. To determine the type of flour, the content of mineral substances that it has is determined and then related to the dry matter. The obtained result is multiplied by 1000, with the obtained value representing the type of flour. For example, if a flour contains 0.550 mineral substances related to the dry matter, it means that the flour is type 550 [11].

In addition to wheat flour, a wide range of other types of flour from sources such as carob, oat, rice, coconut, and buckwheat are used. These have special properties and are used to obtain food products with much higher nutritional values, introduced specifically to improve their quality.

Oatmeal is obtained from hulled and dried oat grain. It has a high content of glycerides, around 6-9%, which induces a very short storage period, especially if it is made at very high temperatures. As a result of this process, fatty substances go rancid, thus giving oatmeal a bitter, unpleasant taste [12]. Glutenin and ovenin are the protein substances present in oat flour that do not form gluten. So, in baking, oat flour is used in a mixture with wheat flour to obtain higher quality products. When using a combination of these types of flour, the baking time of the dough must be longer to allow the complete gelation of the starch and thus obtain a bread with a high specific volume and also with an increased degree of fluffiness and a fine elastic core [13].

Rice flour is a form of flour made from finely ground or polished rice, which can be used as a raw material in the production of various foods. Rice flour offers a number of benefits, especially for rice bread. This is made for patients with celiac disease who are allergic to wheat proteins [14, 15].

Carob flour is produced by deseeding carob pods, yielding kibbled carob, which is further roasted and milled to obtain a powdered product. Carob flour is progressively used in bakeries, with potential benefits for human health and the environment, as it can be obtained with minimal environmental impact [16, 17].

Coconut flour can not only provide improved income to the industry, but is also a nutritious and healthy source of dietary fiber for humans. Coconut flour, which is very rich in fiber, can play an important role in controlling cholesterol, blood sugar levels, and preventing colon cancer [18, 19].

Buckwheat flour is superior to wheat flour due to its higher content of lysine, iron, copper, and magnesium. The significant contents of rutin, catechins, and other polyphenols, as well as their antioxidant activity, are of great importance. These functional components of buckwheat have health benefits such as reducing high blood pressure, controlling cholesterol and blood sugar levels, and preventing the risk of cancer [20].

The potential toxic elements have become a global concern in recent years around the world. The contamination of crops with heavy metals can mainly originate from anthropogenic sources such as mining, the usage of sewage sludge for irrigation, and even the use of fertilizers and pesticides [21-24].

The aim of the work was to monitor the physicochemical quality parameters (color, taste, smell, infestation, granularity, humidity, gluten index, falling number, alveographic properties, ash content, hectoliter mass of wheat) for the raw material: wheat, for the flours resulting from the milling, and for different types of flour and resulting mixtures. The mixtures were made with wheat flour and carob, oats, rice, buckwheat, and coconut flour added in proportions of 5%, 10%, and 20%. Heavy metals (Pb, Cd, Zn, and Cu) were also determined for different types of flour.

Experimental

Results and Discussion

In order to monitor the quality of the flour for consumption, the analysis of the raw material, i.e., the wheat grains, was carried out in the first place. In Table 1, the results obtained from the analysis of the raw material, wheat, used to obtain wheat flour are presented.

Following the results obtained in Table 1, it was found that the analyzed wheat is healthy and of good quality, from which qualitatively appreciated flours can be manufactured. which then help in the process of forming pastry and bakery products.

In Table 2, values for the analyzed metals are presented.

For all types of analyzed flour, the metal concentrations are between the permissible limits defined by the FDA/WHO [24] as 0.41, 0.21, 3, and 27.4 for lead, cadmium, copper, and zinc for whole grain. Lead concentrations were between 0.008 and 0.05 mg/kg, cadmium between 0.013 and 0.026 mg/kg, zinc ranges between 11.33 and 19.6 mg/kg, and copper between 0.33 and 2.56 mg/kg. The results demonstrated the highest lead concentration in wheat flour, the highest cadmium concentration in buckwheat flour, and the highest concentration of zinc and copper in oatmeal flour.

Several studies reported different levels of metals in flours and grains. Ertl and Goessler [32] found levels of Cu in flour within a range of 1.0-8.1 mg/kg and Zn content in grains and flours from 3.8-50 mg/kg, in accordance with our levels. Cu was also found in cereals between 1.8 and 11 mg/kg [33, 34]. Wheat milling demonstrates a reduction in As in grains [35], a decrease in levels of Pb [36], or a reduction in the Cd concentration in cereals [37].

In Table 3, physico-chemical parameters for different types of flour are presented.

For flour 1250, the moisture is low due to the addition of dust during the technological process. The 480 flour has a lower moisture content of 14% due to the lack of water from the wetting process, which cannot reach the core of the wheat grain. At the same time, the 650 flour has a slightly higher moisture content due to the extraction that takes place not only from the kernel of the wheat grain but also from the portions in close proximity to the kernel. The closest moisture to wheat flour is rice flour with 11.3%, followed by oatmeal flour with 9.99% and buckwheat flour with 9.73%. The lowest moisture values are recorded for coconut flour, 6.07%, and carob flour, 5.44%. Zhang et al. [38] found for brown rice flour a value of 6.56% for moisture, while for white corn and rice flour, Djeukeu Asongni et al. [39] obtained a value of 12.5% for moisture content. Different values of moisture are related to the different contents of water in the studied flours. The higher the moisture content, the lower the amount of dry solids in the flour.

The gluten formation process is characteristic of wheat flour and largely depends on the amounts of the two components, glutenin (30%) and gliadin (70%). It was observed that there was a slow decrease in gluten from the type of flour 480, where the largest amount of gluten was found (28.2%), up to the value of 23.6% attributed to wholemeal flour. The lower the degree of extraction of the flour, the more gluten it will have, as only the core of the wheat grain is ground. At higher extractions, the coatings of the grains that do not contain gluten also intervene, and thus it is considerably reduced. From Table 3, it can be seen the total lack of gluten in the rice, carob, buckwheat, oats, and coconut flour.

The fall number, which indirectly measures amylase activity by gelling the flour suspension in a hot water bath and measuring the liquefaction of the gel under the action of α-amylase, indicated values between 260 and 333 seconds for wheat flours, results that support the quality of the flours. The falling number could only be identified for carob and rice flour; the rest of the flours did not record values for this parameter.

For the variation of ash in the wheat flour, it can be observed that this parameter registers the highest value for whole milled flour, 1.4%, and the lowest value, 0.47%, for flour 480. The ash of the flour reflects the amount of mineral substances it contains and is influenced by the degree of flour extraction. The higher the degree of extraction of a flour, the darker it tends to be and contains more minerals due to the grinding of a greater portion of the wheat grain, including the outer hulls. Compared to wheat flour, the lowest value recorded for rice flour was 0.41%, meaning that it has the lowest amount of mineral substances, and the highest was 5.55% for coconut flour. Researchers [39, 40] have associated ash loss with an increase in moisture content.

The granularity of the flours reflects their degree of fineness. As for the granularity of the flours, flour type 480 is the finest flour, while the most granular flour was oat flour with a refusal of 43.5% and 50.6% sifted, and the finest flour was carob flour, where the refusal was 18.4% and the sifted 79.9%. The smell of a healthy flour, obtained from quality wheat and also from a well-established technological grinding process, must be a pleasant one, characteristic of cereals. Any other foreign smell of mold, stale, hot, chemical, or other substances can lead to the flour not being used in the food industry because this unpleasant smell can be imprinted on the finished product, which destroys its quality. The origin of the non-specific smell of the flour can be taken from the ground grains with defects, from the inadequate storage spaces of the flour or from a pest attack. Flour is a hygroscopic product that has the ability to pick up the smell from the surrounding space. The taste and smell of the flours are specific to each ground raw material, without rancid taste or other foreign smells. The degree of coloring of the flours differs depending on the degree of extraction and, ultimately, the amount of ash contained. Djeukeu Asongni et al. [39] reported that the characteristics of breads made from processed flours are better than those of unprocessed ones.

As for infestation contamination, it was not identified in any of the analyzed flour.

Rheological properties are the ones that clearly indicate the quality of flour today. The determination of the deformation energy [W], i.e., the strength of the flour, and the ratio between the maximum pressure in the bubble (toughness) [P] and the average of the values on the abscissa of the breaking points (extensibility) [L] are some of the most important parameters for flour quality. Flour types 480 and 550 recorded exceptional values of the rheological parameters, presenting a W above 200 10^–4J and a P/E ratio of 1.08. Type 650 flour is not inferior either, having a W of 198 10^–4J and a P/E ratio of 1.15. 1250 flour and wholemeal flour are part of the category of black flours that have different rheological conditions compared to white flours. The W of black flours is between 145∙10^–4J for 1250 flour and 178∙10^–4J for wholemeal flour, lower than that of white flours due to the doughs lack of rising power. As for the P/L ratio, it has increased, reaching a value of 2 for the 1250 flour and even up to 6 for the wholemeal flour. The dough made from black flour is lower in gluten, and thus its elasticity is limited. High values of P/L ratios are due to foreign doughs. Following the analyses, it can be stated that black flours cannot be used as such in the manufacturing processes of bakery products, even if they are much more nutritious than white flours, but only in combination with white wheat flours or with the help of food additives, which can help the dough rise and thus obtain quality products. Ge et al. [41] stated that the addition of tannin acid and oligomeric proanthocyanidins significantly improved the rheological property of wheat flour through their interactions with gluten.

Due to the lack of gluten in the five types of flour obtained from varieties other than classic wheat, they cannot be used as such in the technological processes of pastry and bakery because they do not provide strength to the rising dough. So, the five types of flour, carob, buckwheat, oat, rice, and coconut have been added in various percentages (5%, 10%, and 20%) in mixtures with wheat flour and possess particular nutritional properties to give a high-quality finished product. In Table 4, physico-chemical parameters obtained for different mixtures of wheat flour with carob flour, rice flour, buckwheat flour, coconut flour, and oatmeal flour are presented.

The results of the analyzes carried out on the mixtures of wheat flour with carob flour, coconut flour, and oat flour in proportions of 5, 10, and 20% indicated a decrease in the first three parameters, such as moisture, gluten, and the falling index, with an increase in the amount of added carob. Having no gluten, the added carob flour only reduced the gluten already present in the wheat flour. For the mixtures with buckwheat flour, the falling index increased from the value of 460s for the mixture with 5% rice flour to the value of 564s for the mixture with 20% rice flour. This suggests that rice contains a large amount of starch, which automatically indicates an increased presence of alpha amylase in rice flour.

Ash increases with the addition of different types of flour. If, with an addition of 5%, the ash was 0.78%, at 10% it was 0.85%, and at 20% it was 1.28%, it means that carob flour is rich in mineral substances. However, coconut flour, compared to the rest of the mixtures, has the highest recorded values for ash: 0.91%, 0.99%, and 1.75%. As for the organoleptic properties, these intensify with an increase in the amounts of added flours, with coconut flour being the most intense in terms of its strong, pleasant smell and sweet taste. In contrast, oat flour mixes are much more bitter. The granularity of all mixtures in the different combinations showed that these samples were highly granular with an increase in the percentage of non-conventional flours added.

Carob flour has no rheological properties since the gluten content of enriched bread formulations is lower than in white wheat flour, and, in general, blending it with wheat flour negatively affects these properties in the resulting bread. The incorporation of the carob pulp powder increases the deformation energy [42]. Thus, with the addition of 5 and 10% carob flour, the mixture has a W of 212∙10^–4J with a P/L ratio of 1.82, and, respectively, a W of 227∙10^–4J with a P/L ratio of 1.71. These mixtures, although possessing a high P/L ratio, can be used strictly from the perspective of rheological properties in production. The mixture with 20% carob flour showing a W of 254∙ 10^–4J with a P/L ratio of 2.17 is a mixture unsuitable for its use in the processes of obtaining pastry and bakery products. The rheological properties of the coconut and oat flour blends showed high values of W and their P/L ratios, so these mixtures cannot be used in the technological processes of obtaining finished products. The rheological properties identified for the mixtures with rice and buckwheat flours indicate normal values, often used in production processes. It was reported that the addition of phenolic acids to dough decreases mixing time, tolerance, elasticity, and bread volume [43-45]. The P/L ratios for rice flour blends are also slightly increased.

Conclusions

In recent years, due to the desire for the evolution of the technologies used in the technological processes of obtaining food products, an attempt has been made to introduce other types of flour from raw materials other than wheat in the food industry. This idea was born from the desire of technologists to add nutritional properties to food products, but also due to the increase in the number of cases of celiac disease or the large number of people with gluten intolerance. It was also desired to capitalize on certain plants or the waste resulting from certain technological processes and biological resources.

The addition of different amounts of ground flour from raw materials other than wheat in the processes of obtaining bakery products on the classic wheat flour brings an important addition in terms of the amount of dry matter obtained after the calcination of the samples. This indicates that the flours obtained through the mixing process produce great changes in the nutritional values of the finished products. The addition of carob, coconut, buckwheat, oat, and rice flours to mixtures with wheat flour presents a major benefit from a nutritional point of view, thus obtaining much higher quality and more appreciated products.