Nutraceutical properties and secondary metabolites of quinoa (Chenopodium quinoa Willd.): a review

ABSTRACT

Quinoa is a food grain crop that has gained popularity in recent years due to its high nutrient content, phytochemical qualities, and health advantages. Quinoa grain has a high concentration of amino acids, fiber, minerals, vitamins, saponins, and phenolics that can help alleviate various biological diseases in the human body. It contains a variety of biological components and nutraceutical compounds that promote human health. It is an extremely nutritious, gluten-free wonder grain and has the potential to be utilized as biomedicine owing to the existence of functional chemicals that may aid in the prevention of various chronic illnesses. Quinoa has gained popularity in recent years due to its excellent nutritional content and as a component in gluten-free food. It could help to guide the population toward better health. Due to its higher nutritional and health benefits compared to traditional cereal grains, including its high protein concentration, tocopherols, fatty acids, phenolic compounds, phytosterols, low glycemic index, and gluten-free status, it is a promising grain for human consumption and nutrition around the world. The present review paper has been undertaken to provide an overview of the nutrient composition and valuable nutraceutical properties of quinoa.

KEYWORDS:

• Quinoa
• cereal
• biomedicine
• gluten free
• nutraceutical

Introduction

The development of novel and alternative goods is currently a requirement in the food sector. However, the market is flooded with low-quality items and imported products. The only way to increase market share is to employ substances that are different from those that are typically used. The idea of “food” has undergone significant evolution. The body needs food and nutrients to execute its essential activities normally. Some pseudocereals, including quinoa, are good choices in this regard. Numerous biomolecules included in quinoa, such as carotenoids and vital amino acids, may be used to create nutrient-rich dishes for consumption.^[1]

Quinoa (Chenopodium quinoa Willd.), an annual herbaceous plant classified as a pseudocereal, originally thrived in the Andean regions of South America, encompassing Peru, Ecuador, Colombia, Bolivia, and Chile. Remarkably, it stands as a safe dietary option for individuals afflicted with celiac disease.^[2] This remarkable plant has a history of cultivation dating back to 3000 to 4000 years ago, serving as a vital source of sustenance for both humans and animals.^[3] In recent times, quinoa has made its way to diverse continents, including Australia, Europe, North America, China, and Japan. What sets quinoa apart is its adaptability to a wide array of environments, flourishing where other crops might falter. Given these remarkable attributes, the Food and Agriculture Organization (FAO) designated the year 2013 as the International Year of Quinoa. It’s worth noting that quinoa held a central role in the diet of the Inca civilization, and in the Quechua language of the Incas, it goes by the name “chisaya mama” – the mother of all seeds. The reason behind this is that in this period of the Incas and Aztecs, this food was an essential part of their diet, alongside corn and potatoes.^[4] It was known as the “Gold of the Incas” because it was regarded as a beneficial and healing source of life and, hence, was considered a sacred plant. However, after the Spanish downfall, quinoa cultivation was unsuccessful in maintaining its momentum and is now confined to restricted areas of South America.

The production of quinoa in terms of quantity and quality to fulfil the demands of food business in other countries across the world, such as Canada, is being explored. It has a wide genetic diversity and high tolerance to salinity as well as drought. Quinoa is a resilient, drought-tolerant crop with combined annual rainfall and irrigation needs of 25–38 cm, which is significantly less than those of other crops like wheat and rice.^[5] The irrigation should not be applied in naturally damp soil until the crop has two or three leaves. On the other side, over-application of water can induce lodging in quinoa during the seedling stage. In Andean regions, quinoa is often cultivated in rotation with potatoes and grains. However, excessive applications of fertilizer may lead to excessive vegetative growth and lodging.^[6,7]

Despite lower grain yield than other cereals, quinoa production has accelerated recently as a result of increased prices in the global market.^[8] Between 2004 to 2012, farmers sold quinoa at three times and five times the price fetched by soybean and wheat respectively.^[9] Farmers are encouraged to increase the land under cultivation for quinoa for higher economic benefits.^[10] A mature quinoa seed comprises three primary components: a substantial central perisperm, a surrounding embryo, and a one- to two-layered endosperm found exclusively in the micropyle region surrounding the hypocotyl-radicle axis of the embryo. While the quinoa seed does possess one to two layers of endosperm, the majority of starch storage occurs in the perisperm, which constitutes roughly 40% of the seed’s composition. Both the embryo and endosperm of quinoa serve as abundant sources of minerals, proteins, and lipids. Typically, approximately 350 quinoa seeds weigh about 1 gram, with diameter ranging from 1.5 to 4.1 mm and a thickness of 0.6 mm. The color spectrum of quinoa seeds encompasses shades of gray-purple, yellow, white, red, black, and violet. Distinguishing between different quinoa varieties relies on factors such as seed color, plant color, and plant morphology.^[11] Quinoa seeds find versatile applications in culinary creations, including soups, salads, bread, cookies, biscuits, noodles, pancakes, tortillas, and flakes. Additionally, they can be cooked in a manner akin to rice.^[12] For a comparative perspective on nutrient content, Table 1 presents a comprehensive overview of quinoa’s nutritional profile in comparison to other crops.^[13]

Table 1. Macronutrient contents of quinoa and other crops per 100 gram of dry weight.^[13]

	Quinoa	Bean	Maize	Rice	Wheat
Energy content (Kcal/100 g)	399	367	408	372	392
Protein content (g/100 g)	16.5	28.0	10.2	7.6	14.3
Fat content (g/100 g)	6.3	1.1	4.7	2.2	2.3
Total Carbohydrate content (g/100 g)	69.0	61.2	81.1	80.4	78.4

An important characteristic of quinoa is its ability to adapt to adverse environmental conditions. Quinoa can withstand extreme temperatures from 40°C in the South to 2°C in the North, or from the sea level to 4010 m above sea level. Furthermore, it can be grown in tropical, semi-tropical, drought-like situations and cold places as it is frost-tolerant.^[14] Bear, Cherry Vanilla, Cochabamba, Dave 407, Kcoito, Isluga, Kaslala, Linares, Puno, Gossi, Titicaca, Red lighthouse, Redhead, Rainbow, and Temuco are some quinoa varieties that are often cultivated.^[15] There are currently over 250 different varieties of quinoa. The quinoa grain contains a high level of lipids, fiber, vitamins, minerals, and proteins. Quinoa has a higher concentration of essential amino acids than whole grain and processed wheat. It provides a significant amount of minerals and polyphenols.^[16] The pharmacological effects of the polyphenols include antiviral, anti-inflammatory, anti-allergic, cardiovascular, and anti-carcinogenic properties.^[17]

Our review addresses this gap in knowledge by providing an updated overview of the nutrient composition of quinoa. To identify recent pertinent literature, we conducted searches using various combinations of free-text keywords related to Chenopodium quinoa and its nutraceutical properties in the PubMed, Google Scholar and ResearchGate databases.

Methodology

Literature search strategy

To conduct the literature survey, we conducted a comprehensive online search using reputable sources such as PubMed, Scopus, Google Scholar, and ResearchGate. The search employed specific key terms, including “the nutraceutical properties of quinoa,” “the secondary metabolites of quinoa,” “global production of Chenopodium quinoa,” “Chenopodium quinoa for disease cure,” “nutritional value of quinoa,” and “future prospects of quinoa.” The articles included in this review were primarily chosen based on the relevance of their titles and abstracts to the research topic.

Inclusion and exclusion criteria

The inclusion criteria for this review encompassed studies that specifically investigated the nutraceutical properties and secondary metabolites of quinoa. Conversely, the exclusion criteria entailed articles that provided botanical or physiological descriptions of quinoa, articles unrelated to Chenopodium quinoa but pertaining to other pseudocereals, articles not in the English language, those with irrelevant or insufficient data, and articles for which full-text access was unattainable.

Strengths and limitations

We conducted a comprehensive literature search to identify studies that elucidate the nutritional properties and secondary metabolites of quinoa. Out of the initially identified 171 articles, a total of 100 relevant articles were included in this review. The objective of this review is to consolidate and present all available information on the discussed topic in one accessible article, facilitating future research efforts by other scholars. To address the existing knowledge gap in this field, we included studies spanning from 1992 to 2023, encompassing both recent and historical research. However, it is important to note that due to the limited volume of data and literature available on nutritional properties, the discussion of secondary metabolites in this review is constrained by the available information.

Global production

Quinoa has strong nutritional and health potential and is a viable food crop for growth in dry, saline, infertile, and highland agricultural soils because of its high tolerance to extreme environmental circumstances.^[18,19] In marginal areas with high temperatures, limited water availability and precipitation, high salinity, and significant soil erosion and desertification, quinoa is regarded as a key food security crop.^[19–21] Quinoa is an adaptable food that can adapt to challenging environmental conditions. As a result of the growing demand for nutrient-dense, healthy, and gluten-free food in recent decades, quinoa production, trade, and consumption have increased in countries around the world.^[19,21,22] As a result, the harvested area expanded from 52,555 hectares in 1961 to 184,585 hectares in 2019, and the global quinoa production increased from 32,435 tonnes in 1961 to 161,415 tonnes in 2019.^[23] Due to the huge increase in the number of quinoa-producing countries from 8 in 1980 to 95 in 2015, its production dramatically grew to its maximum level in 2015.^[20] Due to population expansion and rising demand for wholesome, gluten-free foods, quinoa output and the number of quinoa producers both will rise steadily shortly.

Nutritional profile

Quinoa, a pseudocereal, is a good source of vitamins, minerals, fiber, lipids, proteins, and dietary fiber.^[24] Quinoa grains are an excellent source of biologically active and antioxidant organic compounds.^[25,26] Chen et al.^[27] classified quinoa into two classes. While group B had more linolenic and long-chain fatty acids, group A had more phytochemicals and polyunsaturated fatty acids. It is possible to use both groups in culinary products. Starch (32–60%), protein (10–18%), and fat (4.4–8.8%) make up the majority of the quinoa grain’s outstanding nutritional profile. Fiber varies from 1 to 14%, while ash, which is mostly made up of potassium and phosphorus, varies from 2 to 4%.^[28] In addition, the grains contain a small quantity of vitamins B and E and a fat-soluble antioxidant. Table 2 shows the nutritional profile of quinoa grains and Table 3 shows the nutritional composition of some meat analogues compared to animal meat.

Table 2. Nutritional composition of quinoa grains.

Nutrients	Quinoa grains	Reference
Crude protein	9.1–15.7%	^[Citation29]
Crude fat	4.0–7.6%
Crude fiber	7.0–14.1%
Carbohydrate	48.5–69.8%
Ash	2.0–7.7%
Energy (kcal)	331–381
Essential amino acids (g 100 g^−1 dry weight)		^[Citation29,Citation30]
Histidine	1.4–5.4
Isoleucine	0.8–7.4
Leucine	2.3–9.4
Lysine	2.4–7.5
Methionine	0.3–9.1
Phenylalanine	0.1–2.7
Threonine	2.1–8.9
Tryptophan	0.6–1.9
Valine	0.8–6.1
Minerals (mg 100 g^−1 dry weight)		^[Citation31–33]
Calcium	27.5–148.7
Copper	1.0–9.5
Iron	1.4–16.7
Magnesium	26.0–502.0
Phosphorus	140.0–530.0
Potassium	696.7–1475.0
Sodium	11.0–31.0
Zinc	2.8–4.8
Vitamins (mg 100 g^−1 dry weight)
Vitamin B1	0.198	^[Citation34,Citation35]
Vitamin B2	0.204
Vitamin B3	0.762
Vitamin B6	0.228
Vitamin E	1.17

Table 3. Nutritional composition of some meat analogues compared to animal meat.^[36]

Product	Saturated fat (g)	Total fat (g)	Fibre (g)	Protein (g)	Calories (cal)	Cholestrol (mg)
Animal Beef	9	23	0	19	290	80
Beyond Burger	5	14	2	20	230	0
Vegan Meat	2.5	16	4	27	270	0
Chicken Nuggets	4	18	0	0	290	40
Impossible Chicken Nuggets	1.5	12	1.5	2	240	0
Veggie Chicken Nugget	1	9	1	4	210	0

*Animal Beef- 113 g; Chicken Nuggets- 95 g.

When quinoa grains are used in food preparation, many steps must be taken to remove antinutritional compound-rich fractions, especially saponins, which are present in the perianth and pericarp, giving the grain its bitter flavor, and harming the intestinal mucosa. The quinoa grains are hand-rubbed and dried after being washed with tap water to get rid of the saponins. However, multiple cycles may be necessary for this procedure.^[36–39] To prevent quinoa seed ingredient modifications (such as starch gelatinization and protein denaturation), which may significantly alter the nutritional and rheological qualities of the quinoa flour, the drying stage is carried out under controlled conditions.

Protein

The quinoa grain is a significant dietary protein source.^[39] Albumins (35%) and globulins (37%) make up the majority of the proteins in quinoa grains, while prolamins make up a smaller portion.^[31] Quinoa proteins are similar to milk proteins in terms of casein content. Quinoa is regarded as a complete diet since its proteins contain all essential amino acids, including tryptophan, histidine, leucine, methionine, isoleucine, lysine, threonine, phenylalanine, and valine.^[3,40] People who frequently consume animal proteins have a problem getting enough protein; thus, their diets should include proteins from plants. Because quinoa does not significantly lose protein content during industrial processing, unlike other typical cereals, quinoa-based products are an appropriate choice in this context. According to electrophoretic experiments, quinoa proteins are divided into the 11S-globulin and 2S-protein big fractions. About 37% of the total protein is made up of 11S-globulin, also known as chenopodium. This fraction has a relatively low amount of the amino acids methionine and cysteine and contains polypeptides with molecular weights of 22–23 and 32–39 kDa. The 2S-protein fraction has a molecular weight of 9 kDa and contains a lot of cysteine, arginine, and histidine.^[41]

Wheat, maize, and rice all have lysine contents that are less than half that of quinoa. Lysine still counts as a limiting amino acid because it makes up 96% of the amount needed to meet FAO requirements in quinoa grains. But among all grains, this is the greatest value ever. The second scarcest amino acid is leucine, yet even this constraint is quite mild. This amino acid is present in 91% of the recommended amount, as per FAO guidelines. For protein separation and characterization, a variety of conventional and contemporary techniques are used. Both wet fractionation and dry fractionation techniques may be used in this. The first one necessitates a significant use of energy, chemicals, and water.^[42] Dry fractionation was more effective than wet fractionation because it preserves nutritional qualities.^[43] The glutamic acid content of boiled (2.1 mg/100 g) and steamed (2.0 g per 100 g) quinoa seeds was reported by Motta et al..^[44]

Protein solubility is a critical parameter when assessing its economic applicability. Higher solubility in proteins is often indicative of greater functional significance. In their research, Cerdán-Leal et al.^[45] delved into the solubility of quinoa seed protein isolate (QPI) across varying pH levels and observed that elevating the pH from 4 to 10 led to an increased solubility of QPI. The solubility range of QPI, as determined by other investigators, spans from 4.08 to 50.38 g/100 g.^[46] This upswing in solubility can be attributed to the higher pH values, which induce alterations in the protein’s structure, thereby exposing more hydrophilic groups. Simultaneously, the carboxyl ionization and deprotonation of amine groups generate negatively charged species, facilitating molecular repulsion and averting aggregation. These findings underscore the heightened solubility of quinoa seed protein in comparison to cereal proteins, a phenomenon potentially linked to the lower molecular weight of quinoa protein.^[47] To illustrate, quinoa seed protein comprises substantial fractions with molecular weights below 50 kDa,^[48] whereas wheat proteins are predominantly characterized by molecular weights ranging from 50 to 5000 kDa.^[49]

Lipids

Quinoa stands out as an alternative oilseed crop, primarily due to its notable lipid content and quality. In comparison to other cereals, quinoa boasts a higher fat content ranging from 5% to 10%, with the majority concentrated in the embryo. Among the lipids found in quinoa, polar lipids, particularly phospholipids like lysophosphatidyl ethanolamine and choline, constitute roughly 25% of the total lipid content. Notably, quinoa oil is abundant in polyunsaturated fatty acids, comprising approximately 63% of the total lipid profile, along with significant tocopherol content at 2.5 mg/g of oil and commendable antioxidant activity.^[50] Within the neutral lipids category, triglycerides make up the bulk at 74%, followed by diglycerides at 20%, monoglycerides at 3%, and the remaining lipids constituting waxes. Predominantly, the fatty acid composition consists of linoleic acid (18:2n-6), linolenic acid (20:3n-6), which accounts for about 55–60% of the total, and oleic acid (18:1 cis–9) at approximately 30%. Quinoa seeds house a rich reserve of omega-6 and omega-3 fatty acids, as well as other essential fatty acids, with the metabolism of linolenic acid and linoleic acid yielding eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), respectively.

Quinoa seed oil is characterized by a significant presence of both monounsaturated (oleic) and polyunsaturated (linoleic and linolenic) fatty acids. Its remarkable stability is attributed to the high concentration of natural antioxidants, including tocopherols, with levels ranging from 69–75 mg/100 g of oil and tocotrienols at 76–93 mg/100 g of oil. However, after the oil refinement process, the quantities of these compounds may decrease by up to 45 and 23 mg, respectively. The exceptional quality and abundant oil content of quinoa grains have led some authors to describe them as “oily pseudo-seeds.” Despite the susceptibility of the lipid fraction to oxidative rancidity due to its high degree of unsaturation, natural antioxidants, especially tocopherols, act as a formidable defense, significantly limiting the onset of oxidation.^[12] Quinoa is also a source of various phytosterols, notably squalene, which exhibits antioxidant properties and supports cardiovascular health and potential cancer treatment. Additionally, quinoa seeds contain substantial amounts of β-sitosterol, a phytosterol known for its ability to reduce low-density lipoproteins. Reports on phytosterols suggest additional biological roles, including anti-inflammatory, antioxidant, anticancer activity, and cholesterol-lowering effects.^[51]

Carbohydrates

Carbohydrates can be categorized based on the extent of polarization into simple sugars (monosaccharides, disaccharides), oligosaccharides, and polysaccharides (such as starches). In addition to being essential for nourishment, carbohydrates can affect many metabolic processes like diabetes, blood sugar, and protein glycosylation. Quinoa seed’s ability to reduce free fatty acids and lessen hypoglycemia symptoms allows it to exert a dietary nutraceutical effect through its carbs. The glycemic index is lower in comparison to pasta and gluten-free bread, which considerably lowers the free fatty acids.^[52] Approximately 67–74% of the total dry matter in quinoa is made up of carbs, while the amylose concentration is close to 11%.^[53] Granules of starch are less than those observed for wheat (2–40 m) or maize (range 1–2 m). Other carbohydrates, such as pentoses (2.9–3.6%) and crude fiber (2.5–3.9%), as well as monosaccharides and disaccharides, are also present.^[54] Quinoa starch’s tiny granule diameter is advantageous for increasing binding and lowering breakability.^[55] Quinoa is said to be an effective thickener for soups, sauces, and flours, according to several pieces of research. Quinoa is more resilient and has a suitably lower gelling point when stored at cold temperatures. Quinoa seeds have a creamy consistency and smooth texture.^[3] Compared to other sugars, sucrose is present in substantial amounts. Despite this apparent distinction, it may be claimed that quinoa and amaranth have extremely similar sugar content.

Fibre

In general, quinoa is regarded as a significant source of fiber. The removal of saponins from quinoa through washing and abrasion has no discernible effect on fiber content. Some studies, such as Alvarez-Jubete et al.^[56] claim that while quinoa’s dietary fiber content is smaller than that of buckwheat, it is comparable to that of cereal and legume grains. The use of quinoa grains has been linked to stomach metabolic abnormalities in rats, according to research using animal models.^[57] Although quinoa’s fiber content differs from that of other cereal grains, research on quinoa’s biochemical properties and therapeutic potential is necessary to comprehend its unique physiological effects.^[58]

Minerals

Quinoa’s outer layers, specifically the pericarp, house an array of essential minerals, including potassium, calcium, magnesium, and phosphorus.^[37,59] When considering the recommended daily allowance (RDA), quinoa emerges as a bountiful source of magnesium, phosphorus, and iron. Notably, the iron content in quinoa, ranging from 8 to 9 mg/100 g, surpasses that typically found in common cereals. However, it’s worth noting that the bioavailability of certain minerals may be significantly reduced by the presence of antinutritional compounds such as saponins and phytic acid. For minerals like iron, zinc, and potassium, various treatments like decortication and ash washing have the effect of diminishing their concentrations by approximately 12–15%. On the other hand, copper and magnesium experience reductions of 27% and 3%, respectively, as a result of these treatments.^[60] Figures 1 and 2 shows the comparison between animal based protein (meat) and quinoa in terms of mineral and fat composition and it represents how much of the daily need can be covered by 300 grams of the meat and quinoa.

Figure 1. Mineral comparison between animal based food (meat) and quinoa (Adopted from https://foodstruct.com/compare/meat-vs-quinoa).

Figure 2. Fat comparison between animal based food (meat) and quinoa (Adopted from https://foodstruct.com/compare/meat-vs-quinoa).

Vitamins

In addition to its abundant minerals, quinoa also boasts a spectrum of micronutrients, encompassing both vitamins and minerals. Vitamins are essential substances vital for human and animal health, with the unique characteristic of being unattainable through synthesis by the human body. Nevertheless, certain compounds within the sterol and carotenoid classes can be transformed into vitamins within the human body, earning them the label of “pro-vitamins.” These vitamins are classified into two groups based on their solubility: water-soluble and fat-soluble, and they have traditionally played a pivotal role in enhancing the nutritional profile of various food items.^[3] While research into the vitamin content of quinoa grains remains limited, some studies have identified notable quantities of pyridoxine (B6) and folic acid in a 100 g serving, capable of fulfilling the nutritional requirements of both children and adults. According to Abugoch,^[61] 100 g of quinoa contains riboflavin levels that meet 80% of the daily needs of children and 40% of adults. Although the niacin content falls short of daily requirements, it remains a valuable dietary source. While thiamine (B1) levels in quinoa are lower compared to oats or barley, riboflavin (B2), pyridoxine (B6), and folic acid levels surpass those found in wheat, oats, barley, rye, rice, and maize. Additionally, quinoa has a higher vitamin E content in comparison to wheat, as previously reported.^[56,61,62]

Secondary metabolites

Saponins

Isolated saponins also offer some intriguing biological characteristics, even though saponins connected to quinoa have been discovered as anti-quality elements.^[63–65] The epicarps of quinoa contain saponins that have a recognizable bitter flavor. The level of quinoa saponin in the study by Stuardo and San Martin^[66] ranged from 0.1 to 5%. Quinoa grains can be characterized as having “sweet” (0.11% saponins) or “bitter” (>0.11% saponins) amounts of saponins, depending on the cultivar.^[67] Saponins may be useful from a pharmacological or nutritional perspective and may become more potent at the intestinal level.^[68] However, since they restrict the digestion and bioavailability of quinoa proteins, saponin concentrations should be reduced during quinoa seed processing. By washing the quinoa seeds in cold, alkaline water and then mechanically abrading them, saponin concentrations can be decreased.^[69] In addition, new quinoa varieties with reduced saponin concentrations (0.11% free saponins) have been developed using a variety of breeding procedures. Quinoa saponins play a pivotal role in enhancing human health through their diverse functional attributes, including antiviral activity, antifungal properties, anticancer potential, antithrombotic effects, hypocholesterolemic benefits, diuretic properties, and anti-inflammatory characteristics.^[70]

Betalain

Betalain, a water-soluble phytochemical present in quinoa, serves as a natural antioxidant and contributes to cancer prevention.^[71] This pigment is responsible for the red, black, or yellow hues observed in quinoa seeds and their vegetative parts.^[12] The betalain pigment comprises red-violet and orange-red betaxanthins, which are nitrogen-aromatic indole compounds derived from tyrosine.^[72] Betalain is prevalent across various quinoa varieties, with some seeds containing betalain concentrations ranging from 0.15 to 6.10 mg/100 g (the total of betaxanthins and betacyanins),^[73] while others show negligible amounts.^[74] Among these compounds, quinoa seeds contain the highest levels of betanin and isobetanin, both boasting health-enhancing properties such as antioxidant, antibacterial, and anti-inflammatory activities.^[16] Notably, betalain exhibits even more potent antioxidant capabilities when compared to polyphenols.^[75] Its multifaceted properties, including anticancer, antibacterial, antilipidemic, and antioxidant effects, position betalain as a valuable component in the realm of functional foods.^[76]

Recent research has explored microencapsulation as a means to stabilize betalain and related substances.^[77] Microencapsulations with low saponin and high betacyanin content exhibit distinctive health-promoting attributes. With its stability in the pH range of 3 to 7, betalain can also be employed as a natural coloring agent. The United States Food and Drug Administration (U.S.F.D.A) and the European Union have approved betalain, designated as E-162, for use as a natural colorant in soups, sauces, dairy products, pharmaceuticals, and cosmetics.^[78] The combination of betalain content in quinoa seed hulls, along with saponins, positions it as a highly advantageous ingredient for the food and pharmaceutical industries.^[79]

Phenolic compounds

Phenols are a family of compounds characterized by the presence of hydroxyl group(s) linked to at least one aromatic hydrocarbon ring. These phenolic compounds exhibit remarkable structural stability and possess substantial antioxidant properties.^[80] In quinoa grains, the free phenolic components per 100 g dry weight range from 167.2 to 308.3 mg gallic acid equivalents.^[81] Notably, in seven different quinoa species, the free percentage of total phenolic content varies between 53% and 78%. Interestingly, ferulic acid and gallic acid emerge as significant components in quinoa leaves, although they are not prominent in the seeds. Diverse types of quinoa contain phenolic compounds with essential roles in mitigating diabetes and obesity.

Phenolic compounds have garnered considerable attention over the past two decades due to their capacity to prevent chronic diseases and promote overall health. These dietary phenolics contribute to gut health by regulating microbial balance within the digestive system. Individual phenolic acids play a role in enhancing metabolism and cell signaling, resulting in potent anticancer, anti-inflammatory, anti-obesity, anti-diabetic, and cardioprotective effects.^[80,82]

Tannins

Tannins, classified as polyphenolic and antinutritional components, can interact with proteins and macromolecules, consequently diminishing the nutritional value of food.^[83] In quinoa grains, tannins are present in minute concentrations, typically ranging from 23.00 to 31.00 mg/100 g.^[84] However, there is currently no available information regarding the presence of tannins in quinoa greens.

Phytic acid

An excess of dietary phytate, which has the capability of chelating bivalent minerals such as iron, calcium, magnesium, and zinc, can significantly inhibit their absorption. Interestingly, even a trace quantity of phytic acid in the diet can contribute to phosphorus storage. However, as of our current knowledge, there is no available information regarding the level of phytic acid in quinoa greens. In quinoa grains, the phytic acid content typically falls within the range of 200 to 880 mg/100 g.^[85] Notably, the phytic acid content in leaves from various types of C. album ranged from 238 to 268 mg/100 g.^[86,87]

Trypsin inhibitor

Trypsin inhibitors (TI) can bind to enzymes, rendering them inactive and thereby inhibiting protein breakdown. It’s worth noting that TI is a thermolabile molecule, meaning that heat treatment can effectively deactivate it. However, there have been no reports of TI detection in quinoa leaves thus far. In a study conducted by Sood et al.,^[88] relatively small amounts of TI were found in C. album leaves, ranging from 0.11 to 0.17 TIU/mg. In contrast, quinoa grains exhibit TI concentrations ranging from 1.36 to 5.04 TIU/mg, which is significantly lower when compared to soybean which have a TI concentration of 24.5 TIU/mg.^[89]

Effect of quinoa on Humans of Different Age Groups

Several experiments on humans were carried out in order to test the effect of quinoa as a food. One such experiment was done by Ruales et al.^[90] on 50–65-month-old boys. They were fed 100 grams of quinoa daily by adding it to baby food for a duration of 15 days, which resulted in an elevation in plasma levels of insulin-like growth factor-1, leading to a reduction in malnutrition. Similarly, De Carvalho et al.^[91] conducted an experiment on women who are overweight and in the post-menopausal stage and made them consume 25 grams of quinoa and cornflakes daily for a duration of 4 weeks, which led to a reduction in levels of triglycerides, low-density lipoprotein, and total cholesterol. Consumption of bread enriched with quinoa flour (20 grams) daily for a duration of 4 weeks resulted in lowering of low-density lipoprotein and blood glucose levels.^[92]

Individuals aged 65 years and older, both males and females, with fasting glucose levels ranging from 100 to 125 mg/dL were made to feed 100% quinoa-based products for the duration of 4 weeks. The result obtained was lowered postprandial glycemia, which is a promising preventive strategy for type 2 diabetes (T2D).^[93]

Role of quinoa in celiac disease

Quinoa’s suitability for the preparation of “gluten-free” food products stems from the absence of gliadins, the gluten-forming proteins commonly found in wheat, and protein fractions akin to gliadin found in oats, barley, rye, and malt. These characteristics hold significant importance as they enable the creation of a wider variety of more nutritious foods suitable for individuals with celiac disease.^[94,95] Celiac disease, a gluten-induced autoimmune intestinal enteropathy, afflicts genetically predisposed individuals upon consuming gluten-containing foods such as wheat, rye, barley, oats, and triticale. This condition is characterized by persistent inflammation of the small intestine mucosa, potentially leading to partial or complete intestinal villous atrophy. Global research has shown that the prevalence of celiac disease is much higher than previously estimated, ranging from 1:100 to 1:300 in the adult population worldwide.^[96,97]

In quinoa seeds, antinutritional substances like saponins, phytic acid, oxalates, tannins, and trypsin inhibitors can be found. Among these compounds, saponins are most concentrated in the outer layers of the grain. Saponin, a natural detergent soluble in water with a bitter taste, can be easily removed through both wet methods like cold water washing and dry techniques such as browning and abrasion.^[98–100]

Concluding remarks

In conclusion, the review of the nutraceutical properties and secondary metabolites of quinoa (Chenopodium quinoa Willd.) sheds light on the multifaceted nutritional attributes and bioactive compounds of this remarkable pseudocereal. Children, the elderly, high-performance athletes, and other members of society all benefit from the energy that gluten-free quinoa grains bring. Quinoa has been a remarkable source of nutrients and a meal supplement for many malnourished individuals all over the world. It is critical to raise awareness among all participants and actors in society about the benefits of quinoa for human health. Quinoa contains important fat-soluble antioxidant vitamins (vitamin B and vitamin E). Quinoa has higher nutritional availability and concentration than other grains. As global interest in quinoa continues to grow, further research and exploration of its potential applications are warranted. Quinoa’s role in promoting human nutrition, food security, and sustainable agriculture underscores its significance in addressing the challenges of the 21^st century.

Disclosure statement

The author(s) did not disclose any potential conflicts of interest.

Additional information

Funding

This study did not receive dedicated funding from any public, commercial, or not-for-profit organizations.