Quinoa and Its Antioxidant and Nutritional Properties and Application in the Food Industry

Abstract

Quinoa (Willd quinoa Chenopodium) is a pseudo-cereal. Quinoa seed is rich in antioxidants and also has a lot of carotenoids. Quinoa seed extract can be used as a natural antioxidant as well as a natural color in many food products, including food edible oils and high-fat dairy products, especially cream, can be used. One of the factors affecting the properties of quinoa seed extract is the extraction method, in which ultrasound and supercritical CO2 extractions are more efficient than green extraction. Therefore, the use of the Carotenoid extract of quinoa has a significant role in stabilizing heat-sensitive oils, especially soybean oil, as well as cream as a new approach to increasing shelf life and reducing the consumption of synthetic antioxidants and synthetic colors in food products.

1. Introduction

Quinoa is a medicinal plant native to South America. The plant belongs to the Chenopodiaceae family. There are about 250 types of chenopodium plant species around the world. Quinoa seeds are the main edible parts of the product and are available in at least three colors, red, black, and white (Figure 1). They are rich in protein with essential amino acids and unsaturated fatty acids including linoleic acid, oleic acid, and palmitic acid, as well as micronutrients such as vitamins, polyphenols, and minerals. The total carotenoid content is in different parts including leaves and seeds [1]. In terms of composition, quinoa seed has 60–69% carbohydrates, 13–20% protein, 9–12.6% moisture, 4–10% fat, about 52–60% starch, and 3–4% minerals (including iron, calcium, magnesium, and zinc), are 10% fiber. Quinoa seeds are considered a source of vitamin E and tocopherols. Quinoa contains more protein than wheat, rye, oats, millet, corn, and rice. Quinoa seeds contain the amino acid lysine, which is an essential amino acid. Quinoa and soy have a similar composition of fatty acids. Therefore, it is considered a rich source of essential fatty acids such as linoleic acid and linolenic acid. The amount of oil in red quinoa is higher than in white and black types. Quinoa seeds contain polyphenols and flavonoids and have more riboflavin and alpha-tocopherol than rice, barley, and wheat [2]. Quinoa seeds have lipophilic carotenoid pigments, which include carotenes, such as lycopene and beta-carotene, which are composed only of carbon, and xanthophylls, such as lutein and zeaxanthin, which contain oxygenated functional groups such as epoxy, carbonyl, hydroxyl, and carboxylic acid groups [1]. Red quinoa contains a high amount of betacyanins, betaxanthins, and flavonoids [3]. Limited research has investigated the value of carotenoids in quinoa seeds. Some researchers have reported the presence of specific carotenoids, such as lutein and zeaxanthin, in quinoa seeds [1].

Figure 1.

The seeds of white, red, black, and tricolor quinoa.

Consuming whole grains, such as wheat, is consistently associated with a reduced risk of cardiovascular disease, diabetes, and obesity due to its rich content such as protein and phenolic compounds. Meanwhile, it is estimated that about 2% and 5% of adults and children with food allergies such as celiac disease, respectively, have gluten intolerance. Cereals are nonherbaceous broad-leaved plants with seeds that can be milled like flour and replace regular gluten-containing flour. Quinoa, amaranth, chia, and buckwheat are gluten-free nutrients. Amaranth and quinoa are highly valued for their protein, dietary fiber, polyphenols, and rich minerals and are consumed as a common grain and vegetable in many cultures. A variety of effective hydrophobic plant substances such as lipids, vitamins, and carotenoids have been found in the leaves, stems, and seeds of both amaranth and quinoa plants [4]. In the food industry, quinoa seeds are prepared as flour mixed with the flour of pseudo-cereals such as buckwheat and amaranth as well as wheat or other grains and are used in the production of products such as bread, pasta, pancakes, biscuits, cakes, and crackers. Quinoa leaves are consumed similarly to spinach or as salad components [5]. The main bioactive compound in red quinoa is rutin (vitamin P), a part of flavonoids. Rutin has anti-inflammatory, antioxidation, and antitumor properties and protects the liver [3]. Due to the presence of essential amino acids such as leucine and isoleucine, quinoa seeds have high nutritional value and quality and are highly digestible. Quinoa proteins have antibacterial, antidiabetic, and blood pressure biological activity [6].

Carotenoids are pigments synthesized by photosynthetic organisms such as plants and some bacteria, algae, nonphotosynthetic fungi, and a small number of prokaryotes. Humans and most animals do not synthesize carotenoids. Therefore, they are included in the diet for physiological functions. The main source of plant carotenoids are mainly roots, flowers, fruits, and seeds [7]. In most plants, carotenoids are found in plastids, especially chloroplasts of photosynthetic tissues and chromoplasts [8]. Carotenoids are the most studied lipophilic natural pigments. They cause yellow, orange, and red colors in corn, carrot, papaya, tomato, watermelon, some fish, and crustaceans [9]. Beta-carotene is one of the most famous food carotenoids that are sometimes found together with alpha-carotene in red and yellow fruits and vegetables such as tomatoes, melons, carrots, mangoes, apricots, pumpkins, etc. Lutein is usually found in yellow or orange fruits and flowers, as well as green vegetables. Zeaxanthin is found naturally in corn, and egg yolk, as well as in some orange and yellow vegetables and fruits such as alfalfa and marigolds [8, 10]. Currently, more than 600 known carotenoids are found in nature, and about 40 carotenoids are regularly consumed in the human diet [11].

Synthetic colors are formulated colors that do not have a natural origin. Adding colored materials to products is required due to things like color replacement for those colors that have been lost during the production process and increasing the existing color. The effectiveness and economic factors provided by artificial colors have led to their widespread use in various industries, including the food industry. Unfortunately, the use of artificial coloring materials or color additives has a negative role in human growth and health, because their toxicity can lead to health problems [12]. Currently, carotenoids produced by chemical synthesis dominate the world market, but their acquisition from natural sources is growing. In fact, according to European Union directives, the importance of natural food additives as an alternative to artificial additives in food, cosmetics, and pharmaceuticals is increasing [13]. In recent years, natural biologically active compounds have received attention due to the interest in natural foods. To meet the demand of consumers all over the world, the food industry has focused on using natural ingredients instead of artificial ingredients. These biologically active substances, in addition to adding economic value, depending on the concentration used, improve the quality of food and even have therapeutic effects. In this sense, carotenoids are natural substances that are often added to food products. Yellow, orange, and red carotenoid dyes are the most common natural pigments used in the food industry as a complete or partial replacement for yellow and red synthetic dyes, which are widely used in beverages and food products due to their stability and high solubility are used [8]. Most carotenoids are derived from the 40-carbon tetraterpenoid phytoene. Phytoene is biosynthesized from two 20-carbon diphosphate molecules [14] (consisting of eight isoprene units with a 40-carbon skeleton) [10]. The central unit usually has 22 carbon atoms, which have nine double bonds and four side chain methyl groups, if they are rearranged by keeping two central methyl groups, it is still classified as a carotenoid [15].

The extraction process is very important in determining the final result of preparing the desired amount of bioactive compounds such as carotenoids. The most important parameters affecting the efficiency of extraction of bioactive compounds from plant sources include matrix properties of a plant part, type of solvent, temperature, pressure, time, solvent concentration, and liquid/solid ratio [16]. Today, there is an increasing demand for the development of green extraction processes, with reduced operating time, better results and extract quality, and a significant reduction in the use of organic solvents. To increase the total yield of plant materials, ultrasound extraction, microwave extraction, and supercritical CO₂ extraction are considered nonconventional methods [17]. Ultrasound is a nonthermal technology that shows a special effect for the extraction of heat-sensitive compounds. The effects of high-power ultrasound to improve extraction is related to acoustic cavitation, which includes: the formation, growth, and collapse of microbubbles in the liquid environment to transmit high-frequency sound waves. The mechanical effects of the ultrasound lead to the release of the desired compounds from the matrix, through the disruption of the cellular tissue and facilitate the penetration of the solvent into the cellular materials. Therefore, ultrasound leads to increased efficiency, increased extraction speed, reduced extraction time, reduced temperature, and the volume of the solvent used. Extraction with supercritical CO₂ is an advanced technology with a high potential for extracting molecules that require standards. The above is in terms of performance without any complications from solvents. They are especially important when extracts are used for nutrients. Extraction with supercritical CO₂ using carbon dioxide in supercritical conditions as an extraction solvent is an alternative to traditional extraction methods [18]. For the extraction of natural compounds, supercritical CO₂ has physicochemical properties between gas and liquid and these properties (such as density, viscosity, and permeability) can be adjusted by modifying the pressure and temperature (always above the critical point). This method is suitable due to the critical point (temperature 31.1°C, pressure 73 atm). It is widely used for its chemical stability, nonflammability, and nontoxicity. Supercritical carbon dioxide has a nonpolar characteristic and ethanol or methanol is added in a small amount (5–15%) to increase the polarity, so it has a significant effect on the extraction of polar and nonpolar compounds [18].

To maintain the safety and effectiveness of food, it is necessary to prevent the oxidation of lipids. In general, the oxidation of food can be inhibited by using natural and synthetic antioxidants. Antioxidants are a type of food additives that are used in the edible oil industry to increase shelf life and inhibit oxidation and degradation of edible oil, which include natural and synthetic antioxidants [19]. The most widely used synthetic antioxidants include Butylated hydroxytoluene, butylated hydroxyanisole, tert-butyl hydroquinone, and propyl gallate. Due to their low cost and high antioxidant activity, they are often used in the edible oil industry as a food additive to prevent the degradation of edible oil. But they have disadvantages including interfering with the synthesis and activity of enzymes, being toxic and carcinogenic, binding to nucleic acid and damaging it, and cell mutagenesis, which produces their effects over a long time and at high concentrations. While natural antioxidants are known as green antioxidants and include simple phenol compounds, phenolic acid, ascorbic acid, tocopherols, carotenoids, flavonoids, vitamins, and anthocyanins. Compared to synthetic antioxidants, natural antioxidants have greater antioxidant activity, increased thermal stability, and increased nutritional value of edible oils, and are more acceptable to consumers [20]. Oxidative stability of the oil is resistance to oxidation during processing and storage, which is an important parameter for determining the quality and durability of edible oil. The production of soybean oil has seen significant growth due to its availability and relatively low cost. One of the most common obstacles to using soybean oil is its level of unsaturation and its sensitivity to oxidation, which mainly leads to a change in taste. Singlet oxygen participates in the initiation stage of lipid oxidation so that it directly reacts with unsaturated fatty acids and creates a mixture of conjugated and nonconjugated hydroperoxides. Carotenoids are a group of fat-soluble pigments that can remove singlet oxygen with multiple conjugated double bonds. The quenching rate of singlet oxygen with carotenoids, lutein, zeaxanthin, and lycopene increases with the increase in the number of conjugated double bonds. Also, the antioxidant property of carotenoids is affected by their concentration, oxygen partial pressure, and environmental conditions. So that beta-carotene reduces the oxidation ion of soybean oil at any concentration and effectively at higher concentrations. However, in high concentrations, it also helps to improve the taste and color of soybean oil [21, 22].

2. Research, results and interpretation

2.1 Extracting quinoa seeds and adding extract to oil

It is possible to extract the bioactive compounds of quinoa seeds through an ultrasound bath, supercritical CO₂ methods. First, red quinoa seeds were powdered for extraction. Then, using ultrasound bath methods (solvent/solid) 50/1) f 100 W and 20 kHz and 45 ± 1°C for 3 min) [23] and supercritical CO₂ (flow rate 15 g/min, temperature 59°C, pressure 350 bar) with two ratios of 10% and 15% ethanol extraction was done by method [24]. The extract obtained from the ultrasound extraction process was purified to prepare carotenoids [25]. In continuation of these two studies, the average total carotenoid content in ultrasound and supercritical CO₂ extractions with 10% and 15% ethanol was determined as 128.568, 120.35, and 121.54 μg/g, respectively [26, 27]. In the following, purified carotenoid extract was added to investigate the effect of the antioxidant activity of carotenoid extract on stability in soybean oil without antioxidants [26, 27]. In ongoing research, quinoa extract was extracted with an ethanol-water solvent ratio (80:20 and 50:50) using the ultrasound-assisted extractionmethod [28].

The number of phenolic compounds was measured by the Folin-Ciocaltio method [29] and flavonoid compounds by the method [30] and antioxidant activity tests such as the ferric reducing antioxidant power by method [31] and DPPH radical inhibition by method [32] and also beta-carotene discoloration test were performed by method [32].

2.2 Oxidative stability of oil

The carotenoid obtained from ultrasound extraction was added to soybean oil with a concentration of 100, 200, and 300 ppm. To evaluate the oxidative stability and the effect of carotenoids on the color of soybean oil, tests such as peroxide value, conjugated diene value, thiobarbituric acid value, and color measurement were performed. 100, 200, and 300 ppm concentrations were compared and soybean oil without antioxidants was also investigated. The samples were kept at 60°C for 8 days [26].

In another study, carotenoid obtained from supercritical CO₂ was added to soybean oil with 10% and 15% ethanol with a concentration of 200 ppm. The tests mentioned in the previous research were also done in this research. Commercial beta-carotene samples with 200 ppm concentration and soybean oil without antioxidants were also examined and compared. The samples were kept at 60°C for 8 days [27].

In ongoing research, quinoa extract (with chitosan wall) was nano-encapsulated. The nano-encapsulated extract was added to the cream. Then, the cream oil was separated from the cream, and then to measure the oxidative stability of the cream oil, the tests of the peroxide value, the thiobarbituric value, and the release of phenolic compounds of the nano-encapsulated extract in the cream oil.

2.2.1 Peroxide value

Oil peroxide value was done by method [33]. The measurement method is based on iodometric titration, where iodine produced from potassium iodide was measured by peroxide in soybean oil. The results of this study showed that 200 mg/kg of commercial and natural carotenoids obtained by ultrasonic bath extraction had the best performance in reducing the PV of soybean oil samples during storage [26]. Concentrations higher than 100–200 mg/kg increase produced peroxide [34].

Samples containing carotenoid extract by supercritical CO₂ extraction with cosolvent ethanol of 10%, and 15% had significantly less peroxide content than samples containing commercial beta-carotene on most days of storage. With increasing storage time, the amount of peroxide increased in all samples containing antioxidants. All the samples on the first day of storage had significantly less peroxide than the samples on the last day of storage. The lowest amount of peroxide on the last day of storage with a value of 7.21 (mEq/kg of fat) was related to the sample containing carotenoid extract with supercritical CO₂ extraction with 15% ethanol solvent [27].

In the ongoing study of quinoa extract on cream oil, the amount of peroxide value was measured by method [35]. In this research, some sample was mixed with acetic acid-chloroform solution in the saturated potassium iodide phase and placed in a dark place. Then distilled water and finally, starch glue reagent were added to it and titration of the sample was done with sodium thiosulfate. Along with the titration of the samples, the titration of the control sample was also performed [35].

2.2.2 Conjugate diene value

For this purpose, soybean oil samples were diluted with hexane (1:600 g/ml). Then, the absorbance of the diluted samples was measured at a wavelength of 234 nm against hexane as a control. To determine the concentration of conjugated diene formed during oxidation, the method of [36] was used. The conjugate diene value of soybean oil samples containing commercial beta-carotene and natural carotenoids obtained from ultrasound extraction at 100, 200, and 300 mg/kg during 8 days of storage at 60°C was investigated. The results showed that the conjugate diene value of the samples containing 100, 200, and 300 mg/kg of commercial antioxidants had an increasing trend in the amount of conjugate diene, which showed that the conjugate diene value in these three concentrations increased during storage. Samples containing 100 mg/kg of commercial beta-carotene had the lowest conjugate diene value during 8 days of storage and showed the lowest conjugate diene value (18.53 mmol/L) on the eighth day. The sample containing 100 mg/kg of natural carotenoids obtained from ultrasound extraction had the lowest conjugate diene value throughout the storage period and it was significantly different from the samples containing 300 mg/kg of natural carotenoids on the first day to the eighth day. According to the findings, it can be concluded that natural carotenoids with a concentration of 100 mg/kg had the highest antioxidant power with the lowest conjugate diene value (16.972 mmol/L) on the eighth day. The sample without antioxidants had the highest conjugate diene value (22.3172 mmol/L) among all samples. Samples containing commercial beta-carotene at the rate of 100 mg/kg had the lowest conjugate diene value until the eighth day. Similarly, those containing 100 mg/kg of natural carotenoids had the lowest conjugate diene value on day 8, that is, the lowest concentration of carotenoids had the greatest antioxidant effect in reducing conjugate diene value on the last day of storage [26].

In another study, oil samples containing commercial beta-carotene and carotenoid extract by supercritical CO₂ extraction method with auxiliary solvent ethanol 10%, 15% increased the amount of conjugated diene with increasing storage time and also in all samples on the first and last day. There was a significant difference in maintenance. Soybean oil containing carotenoid extract obtained from supercritical CO₂ extraction with 10% ethanol and 15% ethanol cosolvent had a significantly lower conjugated diene value in most days of storage, especially in the last days of storage, compared to soybean oil containing commercial beta-carotene. The reason for its higher carotenoid content. On the last day of storage, soybean oil containing natural carotenoid extract by supercritical extraction method with 15% ethanol auxiliary solvent and soybean oil containing commercial beta-carotene with the lowest value of 16.032 mmol/L and the highest value of 19.60 mmol/L, respectively. They had the amount of conjugated diene [27].

2.2.3 Thiobarbituric acid value

A portion of the sample was transferred to a volumetric flask and made up to volume with 1-butanol. Then, the contents of the balloon were stirred. Thiobarbutyric acid reagent was added to the stirred solution. Next, the samples were placed in a water bath and then cooled for 10 min. Then, the absorbance of the solution at a wavelength of 530 nm was read by a spectrophotometer against the control sample. Finally, the amount of TBA was determined in terms of millimoles of malondialdehyde per kilogram of soybean oil according to the method of [37].

Thiobarbituric acid value is widely used as an indicator for the second product of lipid oxidation (malondialdehyde) [38]. The thiobarbituric acid values of soybean oil samples containing different concentrations (100, 200, and 300 mg/kg) of natural antioxidants bath ultrasound extraction obtained from commercial, and were investigated during 8 days of storage at 60°C. The amount of thiobarbituric acid increased during storage with the increase in the concentration of commercial beta-carotene, and the highest antioxidant effect was related to the lowest concentration (100 mg/kg), which had the lowest amount of thiobarbituric acid. On the eighth day of storage, the amount of thiobarbituric acid of soybean oil samples containing different concentrations (100, 200, and 300 mg/kg) of natural carotene was similar to commercial beta-carotene, the sample without antioxidants had the highest amount of thiobarbituric acid. It can be seen that the lowest concentration (100 mg/kg) of both antioxidants was more efficient in reducing the amount of thiobarbituric acid [26]. This can be related to the pro-oxidant properties of carotenoids, including oxygen concentration, the chemical structure of carrot carotenoids, and the presence of other antioxidants such as polyphenols and tocopherols [39]. Not only carotenoids but also other antioxidants are beneficial in increasing the oxidative stability of oils up to a certain concentration above which the pro-oxidant effects of such compounds appear [40].

In another study, in the early days, the amount of thiobarbituric acid is low, but over time, the primary oxidation products increase and begin to decompose, and the amount of this index increases, and volatile aldehydes, the main cause of the bad taste of the oil, are formed. Although in samples containing carotenoid extract extracted with supercritical CO₂ with 10% ethanol from the sixth day and samples containing beta-carotene and carotenoid extract extracted with 15% ethanol on the last day, the amount of thiobarbituric acid was lower than the previous day, which could be due to the oxidation secondary autoxidation products and the formation of carboxylic acids [27].

In the ongoing study to measure thiobarbituric acid value, 1 mg of sample was mixed with 1 ml of thiobarbituric acid reagent and 3 ml of n-butanol and placed in a water bath at 95°C for 2 h. After cooling to room temperature (25°C), the absorbance was measured at a wavelength of 530 nm [41]. Likewise, the release of phenol in cream oil was also tested by the method [29] was measured.

2.3 Color measurement

The color of the oil samples containing antioxidants was evaluated using a colorimeter system using the *b*a*L method. L = parameters indicate brightness, *a = indicates red/green, and *b = indicates yellow/blue [33]. Samples containing commercial carotenoids had lower *a values than samples containing natural carotenoids obtained from bath ultrasound. The highest value was related to the sample with 300 mg/kg of commercial beta-carotene on the eighth day, which was due to the use of this compound in the highest concentration Samples containing commercial carotenoids had lower *a values than samples containing carotenoids obtained from natural bath ultrasound. Samples containing commercial antioxidants had higher *b values than samples containing natural antioxidants. Because commercial beta-carotene was more yellow than natural carotenoid [26]. In all oils containing carotenoid extract obtained from supercritical CO₂ and commercial beta-carotene, the amount of *b is higher than zero and positive and is in the range of yellow color. The amount of index *b of a sample containing carotenoid extracts extracted by the supercritical CO₂ method was higher due to the yellowness of the carotenoid extract added to the oil compared to commercial beta-carotene. Samples containing commercial beta-carotene showed a significant difference during storage at 60°C. There was none between them. The amount of parameter *a in most samples is lower than zero and negative, which can be due to the changes of carotenoid pigments in the oil during storage. The carotenoid extract extracted by the supercritical method with the help of 15%, and 10% ethanol solvents reduced the transparency of the oil samples due to its turbidity and yellowish color. Therefore, they had a significantly lower amount of *L than the samples containing commercial beta-carotene [27].

3. Conclusion

In general, in these two studies, quinoa carotenoids were extracted by ultrasound and supercritical CO₂ methods with the help of 10%, and 15% ethanol solvents, and the total content of extracted carotenoids was measured. Since supercritical carbon dioxide is a suitable solvent for the extraction of carotenoids with low polarity and the selectivity of carotenoids with the supercritical CO₂ method is high and it produces a purer extract than the ultrasound method, as a result, the carotenoid content is higher with the supercritical CO₂ method than with the supercritical CO₂ method. Obtained by ultrasound method. In this sense, the supercritical CO₂ method showed very good performance compared to the ultrasound method. On the other hand, the supercritical CO₂ with the help of 15% ethanol solvent obtained more carotenoid content due to more interaction with the sample matrix than with the help of 10% solvent. Today, in the edible oil industry, synthetic antioxidants such as commercial beta-carotenes are used to improve oil color and strengthen oil to delay oxidation reactions. However, due to the bad nutritional effects of these synthetic antioxidants and consumers’ preference for natural antioxidants, their use as a substitute for synthetic antioxidants has attracted the attention of researchers. Therefore, there is the extraction of carotenoids from red quinoa and its use as a natural antioxidant in soybean oil. The extracted carotenoid extract was purified by ultrasound method and the extracted carotenoid extract by the supercritical CO₂ method as natural antioxidants and commercial beta-carotene as artificial antioxidant were added to soybean oil and all in the same conditions in the oven with a temperature of 60°C for 8 days. To check the oxidation stability of soybean oil by adding the desired antioxidants and to check their antioxidant properties in preventing the formation of primary and secondary oxidation products, the methods of measuring the amount of peroxide, conjugated diene, and thiobarbituric acid were used. The antioxidant showed the highest oxidation rate on most days of storage compared to samples containing antioxidants. Therefore, commercial and natural carotenoids had similar efficiency and there was no direct relationship between carotenoid concentration and its antioxidant effect. As a result, red quinoa carotenoid can be a good substitute for commercial beta-carotene in soybean oil. The extraction of the carotenoid extract with the help of ultrasound and supercritical CO₂ is an alternative based on the principles of green and efficient chemistry in obtaining heat-sensitive natural pigments, which have the potential to be used in food and pharmaceutical fields.