Effects of lingonberry extract on the antioxidant capacity of meat paste

Introduction. Modern meat scientists are currently interested in combining meat raw materials with plant ingredients to enrich products with biologically active substances of natural origin, including antioxidants. In this regard, we studied the antioxidant capacity of a dry lingonberry marc extract introduced into meat paste and analyzed its effects on the product’s color and stability during storage. Study objects and methods. Our objects of study were a dry lingonberry marc extract originating in the Republic of Buryatia, forcemeat, and a ready-made paste in a casing. The extract was obtained by water-alcohol extraction using microwave irradiation. We investigated the physicochemical characteristics of the dry extract, including its contents of phenolic compounds, benzoic acid, and antioxidants. Results and discussion. During the experiment, we analyzed the extract’s effect on the paste’s total antioxidant capacity, coloring, and shelf life. The results showed that increasing the extract’s amount from 0.1% to 0.4% changed the color of the paste from gray-brown to purple-brown, respectively, due to anthocyanins. In further tests, we used a 0.2% concentration of lingonberry extract – the optimal amount that retained the usual brown color of the paste while increasing the content of antioxidant substances. Then, we analyzed the degree of fat oxidation in the paste samples made with and without sodium lactate during storage. According to the results, the lingonberry marc extract used without the acidity regulator and with it inhibited lipid oxidation by 12.7% and 20%, respectively, by neutralizing free radicals. Finally, we tested the presence of pathogenic microorganisms in the end products. We detected no E. coli bacteria in the samples and found an inhibited growth of mesophilic anaerobic and facultative anaerobic microorganisms due to the extract’s bactericidal effect established in Our earlier studies. Conclusion. Thus, our results indicated that the dry lingonberry marc extract introduced into meat paste increased the product’s total antioxidant capacity and improved its stability during storage.


INTRODUCTION
Introducing slaughter by-products into food formulations and technology is a promising direction in the meat industry that ensures a rational use of protein raw materials. Modern meat scientists are developing new products using heat-treated offal of farm animals [1][2][3][4].
Such products include liver sausage, paste, head cheese, and jellied meat. Meat pastes are especially popular. They have a spreading consistency and can be packaged in a casing or container. According to the standards, pastes are classified into "meat pastes" (category A) with at least 20% of muscle tissue and "meat-containing pastes" (category B) with 0 to 20% of muscle tissue. Pastes are affordable meat products due to a lower cost of liver, skirt, lungs, kidneys, and meat trimmings compared to meat. Our meat market traditionally offers pastes in a casing that are popular among students, schoolchildren, tourists, and passengers on trains and planes. These products are made from inexpensive protein-containing ingredients with a high nutritional value and are packaged in small portions.
According to literature, modern meat scientists are interested in combining meat products (including pastes) with plant ingredients to enrich the product with biologically active substances of natural origin (microand macroelements, vitamins, amino acids, antioxidants, etc.) and increase its functional, technological, and other properties.
For example, Gurinovich et al. formulated a meat paste by combining animal protein with that of pine nut oilcake. This way, the authors improved the functional properties of meat systems and enriched the end product with a plant-origin ingredient [5].
Bazhenova et al. mixed forcemeat with wheat flour containing selenium, an essential trace mineral. The authors described how they selected their method of introducing selenium-enriched flour into the forcemeat. They concluded that a 10-15% protein-fat emulsion with selenized flour increased the functional and technological parameters of forcemeat and provided 50-70% of our daily requirement of selenium [6].
Giro and Chirkova proposed enriching paste with iron [7]. They aimed to develop functional meat-based products for people predisposed to, or suffering from, iron-deficiency anemia. Their study showed that offalbased pastes enriched with chickpea could be used to prevent disturbed hematopoiesis caused by iron deficiency. These products contain highly bioavailable microelements that help the body to quickly mobilize its compensatory reactions.
Another study by Okuskhanova et al. looked into the composition and properties of maral deer pastes fortified with beans and protein. The authors developed three formulations with varying amounts of the protein fortifier and beans: no protein fortifier or beans; 15% protein fortifier and 20% beans; and 25% protein fortifier and 10% beans. The study showed that the third formulation had a higher content of essential and non-essential amino acids compared to the first two variants [8].
Pastes from hypoallergenic horse meat and lamb were formulated by Lyakh et al. with the addition of dried dill and Polisorbovit-95, a biologically active dietary supplement. According to their results, this combination of ingredients improved the product's sensory and physicochemical properties [9].
As we can see, meat scientists have created various formulations of pastes with plant ingredients rich in biologically active substances.
Further, modern scientific literature shows increased interest in studying antioxidant capacities of natural plant ingredients in order to introduce them into food products to improve their functional properties and inhibit fat oxidation processes [10][11][12][13][14][15][16][17][18][19][20][21]. Antioxidants can neutralize the destructive effects of free radicals on a human body. Our antioxidant system is one of the main mechanisms for stabilizing our adaptive potential. This is especially important for people who live in adverse environmental conditions and have an unbalanced diet containing synthetic ingredients.
For example, Lisitsyn et al. studied the antioxidant activity of aromatic plant extracts (black pepper, rosemary, sage, and thyme) at the GORO Research Center for Ecological Resources (Rostov-on-Don, Russia). The scientists commercialized a new technology for processing aromatic raw materials -supercritical CO 2 extraction. This technology produces extracts with a significantly different composition from those obtained in traditional ways. Supercritical extracts contain a variety of terpene compounds, as well as waxes, pigments, high molecular weight saturated and unsaturated fatty acids, alkaloids, vitamins, and phytosterols. These substances have high biological, antimicrobial, and antioxidant activities. According to the results, the highest and the lowest contents of antioxidants were found in sage and black pepper extracts (3.1% and 0.07%, respectively). It is generally accepted that natural extracts with an antioxidant content of at least 0.1% can be considered as a dietary supplement with antioxidant properties. Therefore, the authors recommended using sage, rosemary, and thyme extracts as antioxidant ingredients for meat products [10].
Another group of researchers, Zabalueva et al., looked at antioxidant contents in water-alcohol infusions of medicinal plants, depending on the method of their preparation. They found that the concentration of watersoluble antioxidants in infusions obtained by maceration did not differ significantly from those prepared by ultrasound and an ultra-high frequency electromagnetic field. The study showed the potential of using wateralcohol infusions from rose hips and barberry fruits as antioxidant supplements in the production of meat products [15].
A wide range of plant materials (vegetables, fruits, berries, and herbs), including wild plants, are introduced into meat products in the natural form or as extracts, infusions, and decoctions treated in various ways. Edible and medicinal plants are collected, processed, and utilized almost without waste. However, waste from processing wild plants is not always used rationally, being an environmentally friendly, renewable raw material that could be used as a source of biologically active natural substances. These wild plants include lingonberries growing in Transbaikalia (east of Lake Baikal) that are rich in biologically active compounds with medicinal properties. Lingonberry leaves contain phenolic glycosides (arbutin and methylarbutin), vaccinine, lycopene, hydroquinone derivatives, acids (ursulic, tartaric, gallic, quinic, and ellagic), tannin, hyperoside, and other flavonoids. Lingonberries are rich in sugars, ascorbic acid, carotene, and organic acids [22].
The chemical composition of lingonberry leaves and fruits indicates a high antioxidant capacity of respective products. In fact, lingonberries are processed in large quantities for juice production. However, their byproducts -such as husks, pulp or marc -could also be used as a source of biologically active substances. Some authors propose enriching meat products (e.g. liver paste) with fresh or dried lingonberry and cranberry pulp [18,19].
For example, Bitueva and Ayusheeva introduced dried cranberry or lingonberry pulp, pre-crushed and reconstituted, into ground meat products. The powdered pulp was added at the stage of forcemeat preparation, replacing 13-15% of bread. This method enriched the meat products with biologically active substances [18].
In another study, Ivanova and Izosimova proposed a formulation of meat paste with 19% polyfunctional additives -lingonberry or cranberry marc. The marc contains citric and malic acids that shift the medium's pH away from the isoelectric point, enhancing the dissociation of the main and acid groups of protein, as well as increasing bound moisture and the yield of the end product. A high content of low-ester pectins in the berry marc also contributed to the system's stabilization. Biologically active substances and antioxidants increased the microbiological resistance of the meat and plant paste. The product also had an improved vitamin and mineral composition [19].
In our previous work [23], we prepared a wateralcohol extract of lingonberry marc which was then dried. The dry extract is a powder rich in biologically active nutrients that is easy to store and transport. Due to a high concentration of dry substances, the extract can be introduced in small amounts into the formulation of meat products, providing them with functional properties and eliminating negative effects on the product's sensory and physicochemical characteristics.
Thus, it is extremely relevant to create products based on a combination of meat and plant materials to enrich them with micro-and macroelements, vitamins, amino acids, and antioxidants. Many types of plant materials contain a variety of compounds with an antioxidant effect. Even low concentrations of antioxidants in the human body can slow down or prevent oxidation processes which are known to cause premature aging and disease. Thus, we can inhibit fat oxidation by introducing antioxidants into food products.
In view of the above, we aimed to develop a meat paste formulation with an extract from lingonberry marc (originating in Transbaikalia), as well as evaluate the total content of antioxidants and effect on the color and stability of the paste in the casing during storage.

STUDY OBJECTS AND METHODS
The objects of the study included a dry lingonberry marc extract (DLME), forcemeat, and a ready-made paste in the casing.
A dry extract of lingonberry marc was obtained in accordance with Patent No. 2626565. Lingonberries were pressed for juice and the remaining marc was placed on a baking sheet in a 5-8 mm layer and then dried in an oven with infrared radiation at 35-40°C for 40-50 min to 10-15% moisture. The dried marc was crushed to a powder state and subjected to extraction with a wateralcohol solution using a microwave electromagnetic field (700 W, 2450 MHz).
The water-alcohol extracts were filtered and concentrated on a rotary evaporator under vacuum in a water bath at temperature below 45°C until a syrup consistency was reached (40-50% dry matter). The syrup was then vacuum-dried at a temperature below 50°C for 3.5-4.5 h to obtain a powder with a residual moisture of < 5%. Such process parameters do not cause any qualitative changes in thermolabile substances. They preserve maximum biological activity of active substances and ensure high quality of the extract.
The main ingredients in the formulation of paste samples were cheek meat, beef liver, meat trimmings, soy isolate, and semolina. To evaluate the DLME effects on forcemeat characteristics, samples were made with 0.1, 0.2, 0.3, and 0.4% DLME previously dissolved in water in a ratio of 1:5. The paste was made in a casing according to the traditional technology.
A DLME-free paste sample was used as a control. To evaluate the shelf life of the paste, we conducted two experiments. For the first experiment, we prepared control and DLME samples and stored them for 14 days. For the second experiment, we used a 0.2% acidity regulator-sodium lactate (E325) and stored the samples for 18 days.
To evaluate the samples' antioxidant activity, we performed amperometric measurement of the total content of antioxidants in terms of quercetin. The test samples were subjected to extraction with bidistilled water to isolate water-soluble compounds with an antioxidant effect. The total content of antioxidants was measured on a Tsvet Yauza-01-AA analyzer. Quercetin solutions were used to construct calibration graphs [24]. The extraction efficiency was determined by the amount of phenolic compounds isolated spectrophotometrically using the Folin-Ciocalteu reagent. The content of benzoic acid was measured by the HPLC method.
The optical density of the colored aqueous extracts of the test and control samples was determined by the photocolorimetric method on a KFK-3-01 ZOMZ photometer. This method is based on measuring the polychromatic radiation of the visible part of the spectrum. The dependence between light absorption and the radiation wavelength is expressed by a curve (spectrum) of light absorbed by this solution. In the graph, wavelengths are plotted along the abscissa, while optical densities are plotted along the ordinate.
The sensory evaluation of the paste samples was carried out on a nine-point scale according to State Standard 9959. The peroxide value was determined by a method based on the interaction between fat oxidation products (peroxides and hydroperoxides) and potassium iodide in a solution of acetic acid and chloroform, followed by the quantification of iodine released in a sodium thiosulfate solution by the titrimetric method (State Standard R 51487-99 I ).
The microbiological parameters of the paste samples were assessed according to State Standards R 50454-92 II and 9958-81 III .
The experiments were performed in triplicate. Statistical processing of the data was carried out in Microsoft Excel.

RESULTS AND DISCUSSION
First, we analyzed the chemical composition of the lingonberry marc extract originating in Transbaikalia ( Table 1).
As we can see, the main component of the lingonberry marc extract is a group of phenolic compounds (6.63%), including water-soluble pigments, anthocyanins, and benzoic acid (1.34%). In a preliminary study [25], we used the disk diffusion method and found that the extract had antimicrobial activity, partly due to the presence of benzoic acid with bactericidal properties. Thus, introducing the lingonberry marc extract into food products, namely meat, can inhibit the growth of microorganisms. Table 1 also shows a high total content of antioxidants, including polyphenols, anthocyanins, vitamin C, and other compounds (382.6 mg/g). Anthocyanins (3.58%), accounting for half of all phenolic compounds, give lingonberries bright red or burgundy coloring. They include malvidins and peonidins (polyphenolic compounds from the flavonoid group) which contain mono-and diglycosides decomposing into sugar and aglycon (anthocyanidins) upon hydrolysis. Anthocyanins are widely used in the food, medical, pharmacological, and cosmetic industries. A daily intake of brightly colored berries (160-2000 mg) leads to the absorption of anthocyanins (0.005-0.1%), which can have an antioxidant effect. Solutions of anthocyanins neutralize almost all radical forms of oxygen and nitrogen four times as efficiently as ascorbate or α-tocopherol. Even low concentrations of antioxidant substances can slow down or prevent oxidative processes. For example, adding only 0.001-0.01% of antioxidants to oil can slow down its oxidation for a long time [26].
When dissolved, the lingonberry marc extract retains its dark red color. When it is added to gray non-nitrite forcemeat, the latter acquires a purple hue.
Anthocyanins are known to act as pigments and the color of plants depends on their concentration, as well as the medium's pH. They are red in acidic media, purple in neutral and blue in alkaline media. In this regard, we studied how the concentration of the dry lingonberry extract affected the forcemeat pH (Fig. 1).
The forcemeat pH decreased with the introduction of the dry extract, while remaining closer to the neutral region. The extract's acidity was quite high (3.24, see Table 1) due to the use of marc, whose biologically active substances are better extracted into the solution than those of the fruit juice. Therefore, the marc extract is rich in acids (about 2.5%) -citric, malic, benzoic, oxalic, acetic, glyoxylic, pyruvic, hydroxypyruvic, ketoglutaric, ascorbic, and others, with the highest content of benzoic acid (1.34%). This high concentration of acids provides the extract with a low pH, so even very small amounts of the dry extract can significantly decrease the forcemeat pH.
Before the extract was introduced into the forcemeat, it was pre-hydrated for uniform distribution. The DLME concentrations of 0.1, 0.2, 0.3, and 0.4% reduced the forcemeat pH by 1.49, 2.98, 3.7, and 4.47%, respectively. However, the absolute value of the forcemeat pH remained close to neutral, which did not affect the functional and technological properties of the forcemeat system.
Adding the DLME in concentrations from 0.1 to 0.4% affected the forcemeat color. To select the optimal  Optical density D concentration, we analyzed the color characteristics of ready-made pastes in the casing after heat treatment ( Table 2).
As we can see, 0.1% and 0.2% DLME concentrations did not change the habitual sectional color of paste, graybrown or slightly darker. However, larger amounts of the extract (even 0.3%) gave the paste a purple hue. This change is associated with the presence of anthocyanins, water-soluble plant pigments, in the extract.
Lingonberries may contain such anthocyanins as cyanidin-3-galactoside, peonidin-3-galactoside, cyanidin-3-arabinoside, peonidin-3-arabinoside, cyanidin-3-glucoside, and others. However, their qualitative composition depends on the growth conditions. Of great importance for the color of plant pigments is the pH of vacuoles where pigments accumulate. The same pigment in different media can exhibit varying colors: yellowgreen in an alkaline medium, purple in a neutral, and red in an acidic medium [27].
In the DLME, just like in lingonberries, the medium is strongly acidic (pH 3.24), so the color is bright red. When the extract is introduced into the forcemeat, whose medium is close to neutral, it acquires a purple tint from water-soluble anthocyanins. The color, however, depends on the concentration of pigments in the forcemeat.
For the quantitative and qualitative analysis of watersoluble compounds, we determined the optical density of the paste samples with different DLME concentrations, using the spectrophotometric method (Fig. 2).
Optical density is known to be directly proportional to the concentration of compounds in a solution. The scale of the abscissa did not show a significant difference in the samples. However, a thorough analysis indicated that the highest peaks for the control sample (curve 1), 0.1% DLME sample (curve 2), 0.2% DLME sample (curve 3), and 0.3% DLME sample (curve 4) were at wavelengths of 554 nm, 557 nm, 557 nm, and 559 nm, respectively (Fig. 2). As we know, the spectral range from 500 to 560 nm corresponds to purple, while that from 560 to 575 nm to purple. Our study showed the same results: the sample with 0.3% DLME had a violet hue ( Table 2).
Optical density (D) along the ordinate axis characterizes the color intensity. It means that the height of the peaks corresponds to the concentration of dissolved substances (polyphenols) in the samples. As we can see, the optical density values for the control sample (curve 1), 0.1% DLME sample (curve 2), 0.2% DLME sample (curve 3), and 0.3% DLME sample (curve 4) were 0.86, 0.92, 0.93, and 0.93, respectively. The results show that larger amounts of the extract led to higher concentrations of water-soluble compounds, having reached a maximum on curve 4 (0.3% DLME sample).
Thus, we found that increasing the DLME concentration to 0.3% provided the paste with a high content of antioxidants, but added a purple hue to its color due to the presence of anthocyanins, which might spoil the product's appearance.
Antioxidants, including phenolic compounds, neutralize lipid peroxidation, all radical forms of oxygen and nitrogen. Therefore, we analyzed the samples for the total content of antioxidants (Fig. 3). Fig. 3 shows a correlation between increased amounts of lingonberry marc extract and higher total antioxidant capacity of the paste. According to the results, the total antioxidants in the test samples with 0.1%, 0.2%, 0.3%, and 0.4% DLME was higher than that of the control by 1.3 mg/g, 1.5 mg/g, 1.8 mg/g, and 1 -control, 2 -0.1% DLME sample, 3 -0.2% DLME sample, 4 -0.3% DLME sample 2.05 mg/g, respectively. The extract's antioxidant complexes were rich in polyphenols (6.63%; Table 1). They also contained organic acids, vitamins, lycopene, and other antioxidant compounds. Further, we performed a sensory evaluation of the paste on a nine-point scale to establish how the extract affected the product's consumer appeal (Table 3).
According to the results, small amounts of the dry lingonberry marc extract did not significantly affect the texture, smell, or taste of the end product. However, its concentrations above 0.2% had a negative effect on the paste color in section. As we could see in Table 2, the sample with 0.3% DLME acquired a light purple hue and that with 0.4% DLME, a light purple tint. The sensory evaluation showed a concentration of 0.2% as optimal since it did not spoil the characteristics of the end product while enriching it with antioxidant compounds (Fig. 3). Therefore, we used this concentration in further studies. For a physicochemical analysis, we prepared a control and a test sample with 0.2% DLME ( Table 4).
The results showed that the dry lingonberry marc extract did not affect the quality of the paste, but it doubled the total content of antioxidants. The content of phenolic compounds in the extract is the most important indicator of its biological value, which determines its antioxidant activity.
To assess the extract's antioxidant capacity, we studied the process of fat oxidation. For this, we prepared a control and a test paste samples and determined the peroxide value which characterizes the accumulation of primary lipid decomposition products during storage.
Storage periods were selected in accordance with State Standard R 55334-2012 IV (10 days for pastes in polyamide casings and 15 days for pastes with acidity regulators). Our experiment consisted of two tests. In the first test, the control and the test samples (without DLME and with 0.2% DLME, respectively) were made without acidity regulators and stored for 14 days (Fig. 4). In the second test, the control and the test samples (without DLME and with 0.2% DLME, respectively) contained 0.2% sodium lactate as an acidity regulator and were stored for 18 days (Fig. 5).
The reason for this experiment was that acidity regulators are necessarily used in production, especially in summer, to increase the shelf life of perishable meat products. Thus, the experiment could show the DLME role in the inhibition of peroxidation of animal lipids. The samples were stored under identical conditions, in the dark at 2 ± 2ºС. Fig. 4 shows the effect of DLME on the process of fat oxidation in the paste.
In Fig. 4, we can see an irreversible process of fat oxidation with the accumulation of primary fat decomposition products. Animal fats contained in the paste undergo auto-oxidation or peroxidation. The polyamide casing cannot completely prevent oxidation, since it is caused by a complex of factors: oxygen, light, positive temperature, unsaturated fatty acids, etc.
According to regulatory documents, the peroxide value for a high-quality fat product, low-oxidized raw materials, and fat raw materials should not exceed 0.5 mmol, 3.5 mmol, and 10 mmol of active oxygen per 1 kg of fat.
As we can see in Fig. 4    compared to the control. After 10 days (the shelf life for this type of product), the process of lipid oxidation continued to intensify and the peroxide value increased to 3.1 mmol O/kg in the control sample (6.2 as high as the initial value) and to 2.7 mmol O/kg in the test sample (3.8 times as high as the initial value). On day 10, the difference between the control and the test samples reached 12.9%. Further analysis of the oxidation process showed that after 12 days, the peroxide values in the control and the test samples were 3.55 and 3.1 mmol O/kg, respectively. After 14 days, the process accelerated and the values reached 4.1 and 3.7 mmol O/kg, respectively. The difference between the control and the test samples was 12.7% on day 12 and 9.7% on day 14. Thus, the steadily lower peroxide value in the test sample, compared to the control, indicated a decreased rate of lipid peroxidation reactions throughout the whole storage period. This result can be explained by the presence of DLME rich in antioxidant compounds that can neutralize the effects of free radicals playing a significant role in chain reactions of lipid oxidation.
The first test showed that introducing DLME into the paste made without acidity regulators helped to slow down fat oxidation and increase the shelf life by two days (total of 12 days without signs of oxidative damage).
The growth of peroxide values indicated the accumulation of fat oxidation products in the paste samples with sodium lactate throughout storage. However, we found a certain inhibition of the oxidation process compared to the first test, in which the samples were made without an acidity regulator. For example, on day 10, the peroxide values of the DLME samples without and with sodium lactate were 2.7 and 2.5 mmol O/kg, respectively. Thus, we can see a synergistic effect of sodium lactate and DLME antioxidant compounds during fat oxidation in the paste.
Further, we compared the peroxide values in the control and test samples with sodium lactate. We found that after 15 and 18 days of storage, the peroxide value of the test samples was 20% lower compared to the control, which was significantly higher than in the samples without sodium lactate (12.9%).
At this stage, we concluded that a combination of lingonberry extract with sodium lactate produced a more pronounced antioxidant effect. At the end of the storage period (18 days), the peroxide values of the control and test samples were 3.5 and 2.7 mmol of active oxygen per 1 kg of fat. This means that the paste's shelf life could be extended by three days.
Thus, our experiment showed that although DLME contributed to the inhibition of lipid oxidation, its  The shelf life of paste containing a large amount of water (71-72%) is affected by not only oxidative processes, but also by the growth of microorganisms. According to Table 1, the dry lingonberry extract is rich in benzoic acid (1.34%) that has strong antimicrobial, antiseptic, and bactericidal effects inhibiting decay and fermentation processes. As a result, lingonberries last quite a long time without canning. Also, previous studies have proven the antimicrobial activity of DLME added to bakery products [25].
In our study, we investigated a possibility of inhibiting microorganisms in the DLME paste samples with and without sodium lactate ( Table 5).
As we can see, all the samples showed a growth of microorganisms. However, it was less intensive in the DLME test samples with and without sodium lactate, compared to the controls. Thus, the presence of benzoic acid with strong bactericidal action slowed down the growth of microorganisms and had a positive effect on the test samples' shelf life.
As for pathogens, no E. coli bacteria were detected in any of the test samples, which might be due to the preliminary heat treatment of the raw materials and the use of a polyamide casing that excludes the product's contact with air, containers or equipment.

CONCLUSION
Thus, our study showed that 0.2% of dry lingonberry marc extract was the optimal amount to be introduced into paste forcemeat. This amount increased the nutritional and biological value of the paste and maintained high consumer appeal. We found that the extract provided the product with a high content of polyphenols with antioxidant properties, including anthocyanins. Rich in antioxidant compounds, the extract inhibited fat oxidation in the paste and, in combination with sodium lactate, produced a synergistic effect on lipid peroxidation processes. In addition, the dry lingonberry marc extract slowed down the growth of microorganisms due to a high content of benzoic acid with antimicrobial and bactericidal properties. The integrated effect of the extract's components extended the shelf life of the paste in a casing by two or three days.

CONTRIBUTION
Authors are equally related to the writing of the manuscript and are equally responsible for plagiarism.