Introduction

In the modern world, pasta is an integral part of the daily human diet. These flour products have gained their popularity due to their nutritional properties, as well as taste, ease of preparation and the ability to store for a long period.^1,2 Traditional pasta formulations contain a large amount of complex carbohydrates, proteins, vitamins B, iron, and low amount of sodium and fat.^3,4 In addition to wheat flour, in order to increase the nutritional value of these foods, legumes⁵ or other cereal ingredients⁶ are introduced into the composition. Another important aspect affecting the quality of products is the applied technology of grinding grain⁷ and cooking pasta. In previous studies, the use of new approaches in grain processing technology made it possible to increase the degree of preparedness of food products by using extrusive technologies of ready-mixed cereal grain cereal mixture.^8-10

Pasta production consists of such phased technological operations as preparing raw materials for production, dosing raw materials and various ingredients, kneading dough, pressing and forming fresh macaroni, cutting and stacking fresh macaroni, drying and packaging of ready products.¹¹ Drying is one of the most common processes for increasing the shelf life of food products, but also for maintaining or improving their taste and nutritional qualities. In the drying process, food moisture decreases to a certain level in order to minimize microbial spoilage.¹² For pasta, this level is about 11%. During the drying process, moisture first evaporates from the surface of the dough, and then moisture migrates from the inside of the dough. As a result, a moisture content gradient forms in the center of the macaroni and on its surface, and the time required for balancing depends on the thickness of the pasta and the rate of moisture diffusion.¹³

To describe the relationship between moisture content and equilibrium relative humidity, moisture sorption isotherms are studied. These data are useful for understanding the phenomena that occur during the drying or rehydration of food.¹⁴ The equilibrium moisture content allows to optimize the drying time and energy use. In addition, the data gained may be useful for assessing storage stability of food products. Depending on the moisture and temperature conditions, microbial growth, enzymatic reactions, non-enzymatic browning and lipid oxidation are controlled.^15,16 Also, these factors strongly affect the physical properties of pasta – the appearance of cracks and splits, crumbling, shrinkage or swelling,¹⁷ which leads to loss of the products’ vendibility, therefore, to unnecessary costs. The duration of pasta storage also depends on the level of protein and fat enrichment. Fortified foods have a shorter shelf life (2 to 6 months) due to fat deterioration. Without any enrichment, pasta can be stored for one year; it is best stored at lower temperatures.¹⁸ However, in the literature there are no studies of the effect of various poly-cereal ingredients on the sorbing properties of macaroni products, which is very important in connection with an increase in demand for these products.

In previous studies of traditional crops grown in Kazakhstan, we developed formulations of three poly-cereal flour mixtures with high, medium and minimum nutritional values ​​for the production of various food products.^19-22 According to the results of experimental studies of the rheological properties of the test, the addition of dry wheat gluten in an amount of 25% increases the testament elasticity of all formulations.²³ From the point of view of technological processes of kneading and pressing, the optimal moisture level of the test was 31.5%.²⁴ The aim of this work is to study the effect of these three poly-cereal ingredients on the kinetics of drying pasta, affecting the quality of the finished product in terms of taste and presentability of appearance.

Materials and Methods

All experimental and аnalytical studies were conducted in the research laboratory of the ‘Technology of Processing Industries’ research Centre and in the research laboratory of the AgriTech Hub, attached to the Kazakh National Agrarian University.

The object of the study was three types of pasta with various poly-cereal ingredients according to the patented formulations,^19,25 the composition of which is presented in Table 1.

Table 1: formulations of pasta from poly-cereal raw materials²⁵.

Dry wheat gluten (DWG) was added to each mixture in an amount of 25%.

To knead the dough, flour mixtures were used that were obtained by extruded technology²⁶ under three formulations. Pasta from unconventional poly-cereal raw materials was made using the laboratory press machine Götz GmbH.

The rheological properties of poly-cereal dough were studies using modern devices, such as the AlveoConsistograph (CHOPIN Technologies) and the farinograph (Brabender). The drying kinetics of unconventional pasta was studied at a drying temperature of 40° C, 50° C and 60° C. For storage purposes, the required moisture content in a mix is 10%.

Sensory analysis of samples dried and prepared at different temperatures was carried out in accordance with ISO 5496-2005 and ISO 5495-2005 by a qualified tasting group of 5 people from Kazakh National Agrarian University. To assess the quality of food products for several quality indicators, the ISO 3972-2005 scoring method^{38, 56} was used on a 100-point scale.

Results

Figure 1 shows the drying kinetics of unconventional pasta with 25% DWG added for all formulations. As can be seen from Fig. 1 isothermal curves at 40, 50 and 60°C showed different drying rates, which are non-linear. The results of measuring time values upon reaching the required humidity level (10%) are presented in Table 2. With temperature increasing, the drying time decreases by 65-70 minutes. In addition, the drying values for formulation No. 3 at all temperatures are 30-35 minutes longer compared with formulations No. 1 and 2. The shift in drying time that was observed in this case is a result of a complex formulation, including barley and peas, which have high heat capacity.

Figure 1: The Drying Curve for Pasta with 25% DWG Added for Formulation No. 1 (a), No. 2 (b) and No. 3 (c) at temperatures of 40, 50 and 60° С  Click here to View figure

Table 2: Values of drying time at different temperatures for the three studied formulations with 25% DWG pasta.

The nonlinear nature of the isothermal curves can be explained by the fact that the evaporation process can be broken into two stages. During the first stage of drying, the moisture content is related to the heat temperature linearly, due to intense removal of loosely bound moisture. For pasta, the average stage lasts 55 to 65 minutes at 40°C, 35 to 45 minutes at 50°C, and 20 to 25 minutes at 60°C until a critical point, when pasta passes from a plastic to a solid state.

The second stage of drying is characterized by the removal of physico-chemically bound moisture. During this stage, the inclination angle of a curved line of drying decreases until the standard moisture content is reached. Further drying is energy-intensive.

Sensory analysis of 25% DWG pasta of three types after drying at different temperatures shows that all products had a rough surface, rough texture and slight cracks, without extraneous odors and obvious tastes. The differences were only in the color of the products due to the different compositions of the ingredients. Pasta with a high corn content is light yellow, with buckwheat they are light brown. Thus, at this stage, there were no particular differences from the drying temperature.

The next step was testing the cooked pasta. Figure 4 shows all three kinds of pasta dried at 60°C before (row 1) and after cooking (row 2) together with the cooking water that left after the fact (row 3). As can be seen, after cooking, all pasta samples approximately doubled the volume. The cooking water became slightly cloudy, with few pasta fragments left floating in the water. However, all types of poly-cereal pasta have retained their hollow horn shape, resilient texture and color.

Figure 2: Comparative Quality Analysis of Pasta from Poly-Cereal Flour under Three Formulations. Click here to View figure

Data on the sensorial quality of cooked pasta is presented in Table 2. The sensory analysis of cooked pasta indicates high quality of cooked products.

Table 3: Sensorial Findings regarding the Quality of Cooked Unconventional Pasta.

Thus, sensory analysis ranks pasta that was made as follows:

– Good. These are products, made under formulations No. 1 and No.3, which scored 89 points and 93 points, respectively.

Description: slight acceptable sticking; cloudy water after cooking; slightly darker or brighter color; strong taste and odor, which are specific to this grade of pasta;

– Satisfactory. These are products, made under formulation No. 2, which scored 80 points.

Description: mild taste and odor; noticeable sticking after cooking; dark or excessively bright color; cloudy water; soft texture.

Discussion

Considering the results above, the quality of pasta under the three formulations does not change with increasing drying temperature. Thus, from the point of view of energy efficiency in industrial production, the optimal drying temperature will be 60 C, with higher rate of moisture evaporation compared to low temperatures. In addition, at this temperature, the qualitative and nutritional properties of pasta associated with the appearance of cracks and the deterioration of taste characteristics are preserved. Organoleptic analysis of the prepared pasta indicates the high quality of the cooked product. High scores for formulations No. 1 and 3 indicate a balanced composition not only in nutritional qualities, but also in sensory characteristics. According to,^{17, 18} pasta with a lower fat content can be stored for up to a year under conditions of moderate temperature and room humidity of 70%. Since the studied pasta formulations contain a relatively low fat content, while a high level of nutrition depends more on the protein content and low humidity of the dried products, we can assume that the shelf life of the obtained products is 12 months for formulation No. 3 and from 6 months for formulations No. 1 and 2.

In a study of various technological treatments of pasta enriched with 35% legumes showed,²⁷ that drying at 55° C is optimal for maintaining the nutritional properties, digestibility levels of starch and protein network at the macromolecular level. The results of adding bean flour to wheat grits on the quality of cooking and the total phenol content in the paste at drying temperatures of 60, 70 and 80° C²⁸ show that the drying temperature affects the humidity level and cooking time, which increases with the temperature. In addition, the nutritional and qualitative properties of pasta depend only on the amount of the ingredient, which agrees well with the results of this work.

The effect of drying on the pasta structure, starch and protein digestibility, and potential allergenicity at 55, 70, and 90° C were studied in.²⁹ According to rheological measurements, insignificant changes in the structure are observed at drying temperatures up to 70° C. A further increase in temperature leads to a decrease in the starch digestibility and a significant decrease in the protein digestibility. Similar studies of millet-based pasta quality depending on the drying temperature¹² showed that with increasing temperature, water absorption decreased and the color of the product changed. Temperature of 60° C was optimal in terms of product quality. In addition, a number of works also show similar results.^{13, 14, 30} This comparative analysis with other studies indicates the reliability of the results obtained in this paper and the assumptions made.

Conclusion

Thus, based on the results obtained and discussions, we can draw the following conclusions. It was established that the evaporation process occurs in two stages, where in the first the moisture content and the heating temperature are linearly related due to the intensive removal of weakly bound moisture. The time range of this stage is inversely proportional to the drying temperature. At the drying stage, physically and chemically bound moisture is removed inside the dough, with the decrease of the pasta drying speed. A longer process in drying time at all temperatures occurs for formulation No. 3 due to the high thermal resistance of peas and barley, which are part of the mixture. The shortest drying time to a moisture level of 10% is realized at a temperature of 60° C for all three types of pasta. According to sensory analysis of ready products, the qualitative properties of pasta do not depend on the drying temperature, but are only determined by the composition of the additives in the mixture. The highest scores of 93 and 89 after organoleptic analysis were obtained by formulations No. 1 and 3, respectively. Based on the results, the optimum drying temperature is 60° C in terms of product quality and energy efficiency in production for all poly-cereal pasta recipes.

Acknowledgments

This article was supported by the RK Ministry of Education and Science grant within the framework of the 2018-2020 R&D project: “The Development of Technology for Producing Pasta with Unconventional Poly-Cereal Raw Material” (state registration number 0118RK00310).

Conflict of Interests

Authors declare that they have no conflict of interests.

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