Introduction

The greatest challenge of human survival is to meet the food supply demand to the growing population, which is expected to rise 9.8 billion in 2050 (United Nation, 2017). It is also expected that the urbanized area will increase threefold by 2030, which ultimately generate huge pressure on the available production area (d’Amour et al., 2017). Also, the global average daily intake of energy will be increased to 3000 kcal by 2050. Protein as one of the main components of diet played a significant role in the development and physiological functioning of all life forms. Due to increasing pressure to meet the protein demand, animal-based protein consumption is expected to increase, ultimately increasing related environmental problems. This needs identification of new sources and their utilization as food products (Kaur et al., 2022; Langyan et al., 2021a, 2022a).

Plant-based protein sources are extensively searched to meet the protein requirements. From nutritional aspects, the functionality and application of any food primarily depend on proteins. However, their availability in many foods is limited, and the requirements are meet from animal sources (Langyan et al., 2022b; Singh et al., 2022). Food security has been largely dependent on majorly used cereal crops such as rice, wheat, and corn. These grains are an important part of the human diet, yet they lack the essential micronutrients which lead to health concerns (Changan et al., 2017; Chaudhary et al., 2012; Kumar et al., 2014). Also, with an increasing population, it is more challenging to meet the food supply (Langyan et al., 2021b). Hence, the cultivation and utilization of pseudo-cereal crops with a high nutrition profile are of great significance.

Pseudo-cereals, such as buckwheat, amaranth, and quinoa, are considered as the richest sources of high-quality protein, carbohydrates, lipids, vitamins, minerals, and fibers, and also show the presence of bioactive compounds such as phenolic acids, flavonoids, saponins, etc. Pseudo-cereals have beneficial health-promoting effects against cardiovascular diseases, cancer, diabetes, and high blood pressure, and have been used to develop novel functional food products (Priego-Poyato et al., 2021; Thakur & Kumar, 2019; Kalinova & Dadakova, 2009). Additionally, pseudo-cereals have no gluten content and hence widely used in gluten-free formulations. Parameters such as protein efficiency ratio (PER) or net protein use (NPU), bioavailability or digestibility, and index of protein’s nutritional quality, are much higher in pseudo-cereals as compared to cereals (Quan et al., 2018; Upasana & Yadav, 2022).

In today’s era, the globalization of agriculture and its industrialization led to many adverse effects, including high demand for energy, utilization of water, increasing greenhouse gasses (GHG), and climatic disturbances. Moreover, the agricultural land is limited and is under continuous pressure due to different abiotic stresses like temperature, drought, heavy metal, and salinity stress. Additionally, the changes in the climatic conditions also affect food security. However, pseudo-cereals are mainly climate-resilient crops that could be grown in marginal lands not suitable for crops cultivation including low input benefits (Rodríguez et al., 2020).

Although pseudo-cereals are rich in the high level of protein, minerals, amino acids, and non-nutritive components, yet their consumption and commercialization as food products are limited due to gaps in nutritional composition research and limited technologies for their processing and utilization. Also, the supply chain of pseudo-cereals is not well developed, which further limits the availability of these essential foods to the larger population. Hence, the present review comprehensively discusses the current status of these pseudo-cereals in terms of their nutrition and non-nutrition contents, biological functions, food products, processing technologies, applications, and also elucidated the gaps and challenges and provide recommendations for future work.

Pseudocereals: An Overview

Pseudo-cereal is one of any non-grasses plants that are usually used to make bread and other bakery products. The most common pseudo-cereal species known today are Chenopodium quinoa sub sp. Quinoa (quinoa); Fagopyrum esculentum (buckwheat); and Amaranth sps. (amaranth). The seeds of these species mostly resemble true cereals in terms of composition and function, and therefore, they are known as pseudo-cereals (Alvarez-Jubete et al., 2010a).

The South American Andean region (2000–4000 m asl) is known to be the native for quinoa species (Chenopodium quinoa Willd.). The weedy species of quinoa, known as Chenopodium album, is commonly referred to as pigweed in English and “Bathua” in Hindi. This species of quinoa is resistant to frost and grown in regions having less rainfall (300–400 mm). It has smaller seeds with diameter in the range of 1 to 2.5 mm and reaches up to 1 to 3 m high, while the roots dig up to 30 cm into the soil. The stem with a diameter of 3.5 cm is cylindrical in shape, having a branched stem with a variety of colors (white or yellow). The grain is covered with pericarp containing saponins and made up of two layers. Before consuming it as food, the saponins (bitter material) should be removed. Due to excellent adaptability, the quinoa production can be seen in various geographical regions around the world. It has been cultivated in Asia, mainly the Himalayas and Northern India plains produce higher yield. Additionally, the grains of quinoa produced in Japan contains large number of bioactive components as compared to other cereals as well as pseudo-cereals (Dabija et al., 2022; Mir et al., 2018; Pritham et al., 2021). Due to high nutritional composition, quinoa is known as “food for astronauts” (Yasui et al., 2016).

The buckwheat (Fagopyrum esculentum Monch) is originated in China, and then it was moved to Eastern and Central Europe by nomads. During thirteenth century, the buckwheat production has increased in Italy, Austria, and Germany, but thereafter its cultivation was lost due to the introduction of other cereal crops. Nowadays, the cultivation and utilization of buckwheat are continuously increasing due to increasing demand for the gluten-free diet, and hence the global production goes higher. The highest production of buckwheat (1.19 million tonnes) was recorded in Russia, followed by China and Ukraine (FAOSTAT, 2018). In European countries, the buckwheat is cultivated largely in Poland (72,096 MT), followed by France (124,217 MT), and there is very less production in Lithuania, Slovenia, Hungary, and Latvia. Japan is known to be the largest consumer of buckwheat, and it is consumed as the second food crop after rice. The buckwheat can be cultivated in different types of soil, and is considered as the highly nutritious crop containing high protein content (Upasana & Yadav, 2022).

Globally, there is a large biodiversity of amaranth, and among various varieties, Amaranth caudatus, Amaranth cruentus, and Amaranth hypochodriacus are majorly cultivated and grown for their seeds (Kaur et al., 2010). Generally, seeds of amaranth are convex in shape, having weight of 1.3 mg and diameter in a range of 1–1.5 mm. The amaranth crop is heat, drought, and pests resistant and also tolerates poor soils and arid conditions (Mir et al., 2018).

Pseudocereals: Nutritional and Anti-Nutritional Components

Pseudocereals have recently, attracted the attention of various researchers in food science and technologies as well as nutritionist due to higher nutritional composition. The nutritional composition of the pseudo-cereals (amaranth, quinoa, and buckwheat) is given in the Table 1. The nutritive value of these pseudo cereals is even higher to that of the true cereals. Therefore, a nutritional composition comparison of pseudo cereals with trues cereals (wheat, rice and maize) is presented in the Table 2.

Table 1 Principal nutritional composition of pseudocereals (quinoa, amaranth and buckwheat)
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Table 2 Nutritional composition comparison of pseudocereals with the comparable cereals
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Proteins

With the presence of essential amino acids, one can determine the protein’s nutritional quality. A lack of single amino acid results in diet leads to poor development, growth, and metabolic syndrome in humans and livestock. It has been reported that the protein content in pseudo-cereals is more than in cereals (Pirzadah & Malik, 2020). Interestingly, the lysine that is poorly distributed in cereal proteins is found higher in pseudo-cereals. Amaranth and quinoa also contain a high amount of histidine and arginine, which are good for children's and infants’ nutrition. Recently, it has been observed that proteins present in quinoa can provide many essential amino acids such as histidine (210%), lysine (132.22%), isoleucine (107.33%), methionine + cysteine (157.72%), threonine (177.82%), phenylalanine + tyrosine (247.63%), valine (107.43%), and tryptophan (15.83%) for adult nutrition (Mir et al., 2018). The sulfur-containing amino acids like methionine and cysteine are also present in higher concentrations in pseudo-cereals compared to commonly used cereals like rice, sorghum, and wheat. It has been reported that the leaf of quinoa is considered the best source of protein that can be used in fodder and in pharmaceutical industries (Martínez-Villaluenga et al., 2020). The processing techniques like fermentation and popping showed positive effect on amaranth grains. It has been reported that popping enhances the total lysine content of amaranth grains, which is higher than commonly used cereals. However, there is a limitation of using fermentation and popping methods as they are linked with reducing exogenous factors (e.g., trypsin, phytate, and tannin inhibitors), thereby decreasing the digestibility of proteins. Pseudo-cereals also contain storage proteins of different properties and structures, such as albumins (2S) and globulins (11S and 13S).

Carbohydrates

In carbohydrates, starch, a major energy source, is a biopolymeric component in plant parts (seeds, tubers, and grains) that is generally found in the seed’s perisperm in simple or spherical shapes (Garg et al., 2020). Quinoa contains carbohydrates ranging from 67–74% of its dry weight; however, the content of amylose is lower (11%) than cereals. Starch granules of quinoa are smaller in diameter than maize and wheat, and exhibited higher temperature of gelatinization (e.g., 57–64 °C). Other carbohydrates are usually present in very low amounts. These includes, monosaccharides (2%), disaccharides (2.3%), pentosans (2.9–3.6%), and crude fiber (2.5–3.9%). It has been reported that starch extracted from quinoa is helpful in those applications where breakability reduction and binding improvement are needed (Jan et al., 2016). Compared to amaranth and quinoa, buckwheat contains a large amount of starch and provides higher energy. For example, 100 g of grains of buckwheat gives the energy of 343 cal.

Dietary Fiber

The concept of dietary fibers is less known in pseudo-cereals. Quinoa and amaranth are considered as health-promoting pseudo-cereals due to high nutritional content. In one of the studies, the overall composition of seeds of amaranth contains dietary fiber ranging from 8 to 16%, and out of this, approximately 33–44% were considered as soluble fibers. Compared to quinoa and amaranth, dietary fiber content is higher in the seeds of buckwheat (Alvarez-Jubete et al., 2010b). The composition of monosaccharides in insoluble fibers of amaranth was recorded as 57% glucose, 9% xylose, 22% arabinose, 6% galactose, 4% rhamnose, 2% mannose, and 1% fucose. The insoluble dietary fibers of amaranth and quinoa are composed of homogalacturonans dispersed with RG-I stretch. The amaranth contains a higher fraction of soluble dietary fiber content than quinoa. Soluble fibers of quinoa are mainly consisted of arabinans and homogalacturonans. In contrast, soluble fiber present in amaranth consisted of branched xyloglucans, having side chains of disaccharide and trisaccharide, and has different fermentative and physiological properties (Mir et al., 2018).

Minerals and Vitamins

In general, minerals such as iron, magnesium, and calcium are present in less amounts in gluten-free foods and products. Pseudo-cereals such as quinoa, amaranth, and buckwheat are excellent sources of magnesium; calcium, iron, and other vital minerals (Alvarez-Jubete et al., 2010a). The highest amount of minerals is present in amaranth, followed by quinoa and buckwheat. Vitamins played a major role in almost every physiological function. The content of thiamine is more in amaranth as compared to wheat. Amarnath and quinoa are excellent pseudo-cereals for vitamin C, riboflavin, vitamin E, and folic acid contents, whereas Tartary buckwheat seeds contain higher content of vitamins B2 and B6 (Patil & Jena, 2020).

Fatty Acids

Pseudo-cereals have the highest number of fatty acids compared to other cereal crops, mainly characterized by a large amount of unsaturated fatty acids (linolenic acid). The highest amount of linoleic acid was found in amaranth and quinoa, whereas the oleic acid level and eicosenoic acid were found highest in buckwheat (Dziadek et al., 2016). The level of eicosnoic acid and erucic acid was also reported higher in quinoa. Among saturated fatty acids, palmitic acid was reported higher in amaranth, followed by buckwheat and quinoa (Bock et al., 2021). Polyunsaturated fatty acids improve insulin sensitivity and also cure cardiovascular diseases, osteoporosis, cancer, autoimmune, and inflammatory diseases. A high quantity of squalene was found in amaranth, which is widely used in cosmetic and pharmaceutical applications. The content of lipid present in quinoa and amaranth is 2–3 times higher than wheat and buckwheat (Mir et al., 2018).

Anti-Nutrient Components

Various anti-nutrient components are present in pseudo-cereals. These commonly include polyphenols, which are reported higher in pseudo-cereals than other cereals. Phenolic acid was found higher in buckwheat, followed by quinoa and amaranth. Among the phenolic acids, gallic acid, dihydroxybenzoic acid, vanillic acid, caffeic acid, o-coumaric acid, and rutin were commonly reported in pseudo-cereals (Dziadek et al., 2016). Anthocyanins and flavonoids are other polyphenolic compounds present in pseudo-cereals. The higher content of anthocyanin and flavonoids is present in buckwheat, followed by quinoa, and amaranth (Mir et al., 2018). Pseudo-cereals also contain saponins, phytosterols, phytoecdysteroids, polysaccharides, tannins, oxalates, and phytates (Fig. 1) (Hernández-Ledesma, 2019).

Fig. 1
figure 1

Major antinutrients available in the pseudocereals. Compiled from Popova and Mihaylova (2019) and National Center for Biotechnological Information (NCBI, 2022)

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Bioactive Properties of Pseudocereals

Reports have been published on various bioactivities of pseudocereals, which majorly include antitumor, antioxidant, hypoglycaemic, ACE inhibitory, antimicrobial, and hypolipidemic effects (Table 2, Fig. 2). It has been observed that in countries where a high number of cereal crops are consumed, the risk of several diseases related to the metabolic functions has been greatly reduced. Lectins present in pseudo-cereals activated the innate defense mechanism, preventing cancer and obesity. On the other hand, protease inhibitors also have potent ACE inhibitors and anti-inflammatory properties and were closely linked with anti-hypertensive effects (Langyan et al., 2022a). Dietary saponins form insoluble cholesterol complexes, thereby lowering plasma cholesterol levels and decreasing the occurrence of cardiovascular diseases. Also, phenolic compounds like flavonoids, tannins, and phenolic acids, having a significant role in the pigmentation of seeds showed higher antioxidant activity (Giusti et al., 2017). The bioactivities of small peptides present in pseudo-cereals are mainly released from enzymatic hydrolysis by various proteases such as pepsin, trypsin, chymotrypsin, alcalase, papain, pancreatin, thermolysin, and flavourzyme (Awika & Duodu, 2017). These peptides have various bioactivities such as antioxidant, antifungal, antitumoral, and ACE inhibition activity, and are also used for different purposes, like food supplements, functional food ingredients, and nutraceuticals (Table 3) (Awika & Duodu, 2017; Das et al., 2020).

Fig. 2
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Bioactivities reported from pseudo-cereals

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Table 3 Bioactivity of psuedocereals
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Pseudo-cereals, mainly quinoa, buckwheat, and amaranth, showed antidiabetic, anti-hypertensive, antioxidant, anti-inflammatory, immunoregulatory, anticancer, neuroprotective, and anti-microbial activity (Table 3). These bioactivities are mainly exerted by the protein hydrolysate or the isolated peptides by various mechanisms. For instance, the antidiabetic activity of pseudo-cereals is mainly due to inhibition of dipeptidyl peptidase IV (DPP-IV) and α-amylase and α-glucosidase activity, anti-hypertensive due to angiotensin-I-converting enzyme inhibition, and hypocholesterolemic effect due to inhibition of pancreatic lipase and HMG-CoA reductase activity (Del Hierro et al., 2021; Nongonierma et al., 2015; Sánchez-López et al., 2021; Soares et al., 2015; Vilcacundo et al., 2017; Zieliński et al., 2020).

Pseudo-cereals have also been tested clinically against different disease conditions and/or to fulfill the nutrients requirements. Quinoa and quinoa-based products (e.g., biscuits, crackers, brioche, sponge cake, baguette bread, sliced bread, and pasta) have been tested and found effective in preventing type-2 diabetes mellitus in the diabetic patient with age > 65 years (NCT04529317 dated Sept’ 2016). Also, buckwheat was found effective in lowering the blood glucose level in diabetic adults (NCT00841503). It has also been reported that quinoa effectively reduced weight and other complications (e.g., glycemic index) in overweight persons (NCT02621502). Biscuits made from quinoa were found effective in preventing cardiovascular risk markers in older patients (NCT03291548). The probiotic potential of quinoa milk was investigated in adults and found to change the composition of oral and intestinal flora. Due to its high level of amino acids and free from lactose, gluten, and cholesterol, the fermented quinoa milk provides a more effective probiotic effect (NCT04280731).

Irritable bowel syndrome (IBS) is one of the most common challenges in digestion and after that avoidance of nutritious food products. In a clinical study, the Sourdough wheat bread, regular yeast baked toast bread, and gluten-free diet containing quinoa were tested in adults. It was found that the gluten-free diet containing quinoa prevents IBS and provides a nutritious diet as compared to others (NCT02572908). Chenopodium formosanum and buckwheat extract drink were found effective in preventing the aging effect (NCT04237818). Buckwheat honey was prepared and tested for its preventive effect against cough with acute upper respiratory tract infection in adults. It was found that the buckwheat honey significantly reduced the frequency and severity of cough compared to placebo (NCT01062256). Food prepared with olive, buckwheat, peas, and chestnut flour was found effective in modifying the gut microbiota and the cholesterol metabolism in obese and hypercholesteremic patients (NCT02664428). Amaranth flour improved diet quality and iron intake in children (12–59 months), thus preventing anemia (NCT01224535).

Processing Techniques of Pseudocereals

For improving the nutritional quality of pseudo-cereals and inactivating/eliminating the compounds that interfere with the digestibility of protein, various processing techniques such as cooking, soaking, dehulling, microwave, irradiation, extrusion, and fermentation have been used. During food processing, heat treatment has been widely used for different purposes like sterilization, enhancing texture and flavor, destroying toxic microorganisms, and improving functional and physical properties. The effect of processing techniques on the nutrients (carbohydrates, protein, oil, dietary fiber, etc.) and anti-nutrients (phytates, oxalates, saponins, etc.) in the pseudo cereals is presented in Table 4. These processing methods are useful in improving the protein quality and the digestibility of proteins. However, some adverse effects like protein degradation have also been reported due to thermal processing, affecting the bioavailability of essential amino acids. Several studies postulate the effects of food processing on the digestibility and nutritional properties of proteins from pseudo-cereals. These commonly include conventional grain processing (milling, roasting, drying, cooking, baking) and bioprocessing (enzyme-assisted processing, fermentation, biorefinery). Some of them are used during the processing of pseudo-cereals and are discussed below.

Table 4 Effect of processing techniques on the nutrients/antinutrient in the pseudocereals
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Cooking

Cooking, being one of the most important and common process, influences nutrients bioavailability, nutritional value, and digestibility (Kalpanadevi & Mohan, 2013). With the presence of heat-labile compounds in uncooked proteins, the digestibility of protein is low. Hence, cooking has several effects on the digestibility of proteins like denaturation of proteins or reducing the protein resistance from the enzymatic activity and interacting proteins with non-protein components, which further affect the digestibility. The cooking method also destroys the protease inhibitors, and unfavorable compounds are leaching out and improve digestibility. It also eliminates trypsin inhibitors and reduces the content of phytic acid and tannins ((Fawale et al., 2017). In extrusion cooking, the high temperature and pressure were applied, resulting in high shear forces and very short cooking time. The high heat and pressure cause protein denaturation, while the nutrients are retained due to very low exposure time. A high shear force is required for pseudo-cereals compared to rice and wheat processing due to high lipid and lower amylose content. In amaranth and quinoa, the fat content is higher, and thus it needs to be blended with flour having low-fat content, such as rice or maize. Also, these pseudo-cereals need an additional defatting step before extrusion cooking. In buckwheat, the fat content is lower and could be directly used for extrusion cooking. Maize blended with amaranth or quinoa undergoes extrusion cooking to produce expanded extrudates, with lower tocopherol and fatty acid content, while the phenolic compounds and folate are partially affected (Ramos Diaz et al., 2017). The extrusion cooking also affected the physical and biochemical properties of the pseudo-cereals. For instance, the quinoa under extrusion cooking increased the protein crosslinking and the soluble fiber content, while some essential amino acids such as valine and methionine were slightly reduced (Kuktaite et al., 2021). Due to the presence of aggregated starch compounds in quinoa, the starch is not completely gelatinized after extrusion cooking, which can be overcome by adding sufficient water during the extrusion cooking following drying of the extrudates (Kuktaite et al., 2021). After cooking, the prepared extrudates were milled and showed improved water solubility, protein solubility, oil binding, and foaming properties (Espinosa-Ramírez et al., 2021).

Steaming and boiling are the two most common cooking processes used for most foods, including pseudo-cereals. In a study, both these cooking methods were analyzed for their effect on the mineral content of quinoa, amaranth, buckwheat, and rice. It was found that during steaming quinoa, the manganese, phosphorus, and iron retain 100%. On the other hand, in all the pseudo-cereals, the mineral content in steaming and boiling processes showed no significant differences (Mota et al., 2016). The effect of roasting and boiling on amaranth and quinoa seeds was profound as it increases the bioavailability of minerals, dietary fibers, and phenolics (Repo-Carrasco-Valencia et al., 2010). Also, it was found that roasting improved the gruel viscosity of amaranth as compared to raw and popped grain (Muyonga et al., 2014).

Microwave and Irradiation

Microwave energy utilizes electromagnetic waves having a frequency between 300 MHz and 300 GHz. It is non-ionizing radiation that continuously generates heat because of molecular motion in the product (Divekar et al., 2017). It generally improves functional properties like foaming, emulsifying, and water and oil holding capacity. This method inactivates protease inhibitors, reduces bioactive compounds concentration, and enhances protein quality (Vagadia et al., 2018). Irradiation is a safe method where food is exposed in ionizable radiations with a specific time interval and environment under controllable conditions. It can help avoid various diseases caused by microbes and remove unfavorable compounds, hence improving the protein quality. However, it has a negative impact on protein digestibility as it degrades specific amino acids (like sulfur and aromatic amino acids).

Germination

Germination is the absorption of water by dormant/dry seeds, leading to embryonic axis elongation. During germination, mostly hydrolytic enzymes result in biochemical changes, modify structural properties, and enhance the nutritional value, thereby reduce antinutritional factors by leaching or enzymatic activity. With the improvement of the digestibility of proteins after the germination process, a reduction in phytic acid and polyphenols content in germinated seedlings were recorded along with an increase in the protein solubility (Albarracín et al., 2015).

Water soaking before germination played a major role in the development and growth and the nutritional characteristics of the germinated plant. As such, the slightly acidic electrolyzed water was tested in buckwheat and showed an increase in the GABA, rutin, glutamic acid decarboxylase (GAD), and phenylalanine ammonialyase (PAL) activity (Hao et al., 2016).

Drying

Several drying methods are used for the removal of water molecules present in the food. These methods include hot air-, sun-, freeze-, spray-, and vacuum-drying. Among them, spray-drying is widely used in the food industry to enhance the shelf-life of food. Spray drying mainly uses high temperatures, decrease heat-labile substances within the proteins and affecting the digestibility and functional properties of the protein. Hot air spraying is mostly used to dry liquid foods through moisture vaporization and hence leaves the particulate matter in the form of powder. The freeze-drying process undergoes sublimation, which helps increase aggregations and protein–protein interactions. Also, improve the digestibility of proteins and enhance various functional properties like solubility of the protein, water-holding capacity, foaming, and emulsifying properties (Tontul et al., 2018).

Fermentation

It is the process that utilizes several microorganisms such as yeasts and bacteria that help to improve the nutritional quality of crops. It also enhances the texture, aroma, and flavor of bakery foods. It increases protein availability, functionality, and eliminate undesirable compounds. Fermentation also played a major role in improving the bioavailability and digestibility of nutrients (Fawale et al., 2017). Pseudo-cereals are mainly used for bread making; however, due to lower palatability, it have been fermented with P. pentosaceus, E. faecalis, W. cibaria, L. plantarum, L. salivarius, L. rhamnosus, and L. paracasei (Capuani et al., 2013; Rocchetti et al., 2019a, b; Zieliński et al., 2017, 2019). The lactic acid bacteria fermentation improves the palatability and aroma of pseudo-cereal products. With the help of L. paracasei and L. plantarum, Tartar buckwheat flour was fermented and showed antidiabetic activity (Feng et al., 2018). Also, it has been reported that with the help of lactic acid bacteria, the quinoa pasta product was made, which further improved the vitamin and mineral content in a mouse model (Carrizo et al., 2020). Also, lactic acid bacteria fermentation improves the antioxidant and phenolic content of pseudo-cereals (Bustos et al., 2017). A bread prepared using amaranth (Amaranthus caudatus, grown in India), quinoa (Chenopodium quinoa, grown in Canada), and buckwheat grains (Fagopyrum esculentum Moench, grown in China) and yeast was analyzed for vitamin E content. It was found that the bread prepared using quinoa has the highest content of vitamin E (alpha-tocopherol), whereas amaranth bread contained the highest beta and delta-tocopherol content. Gamma-tocopherol content was highest in both buckwheat and quinoa. It was also recorded that the vitamin E content in the pseudo-cereals made bread was higher than the bread made from wheat (Alvarez-Jubete et al., 2009). Also, the loss in the vitamin E content during high-temperature baking was reported, and pseudo-cereals bread showed lower loss than wheat bread. Among them, the lowest loss in vitamin E content was recorded in quinoa bread.

The bread made from gluten-free pseudo-cereals uses processing techniques such as sourdough technology, high hydrostatic pressure, milling, and non-conventional baking methods (Bender & Schönlechner, 2020; Sciarini et al., 2020). It has been found that sourdough improved the quality of buckwheat and amaranth bread (Bender et al., 2018; Houben et al., 2010). In recent years, ohmic heating has been used in the baking process and has provided significant functionality and digestibility compared to the conventional process Bender et al., 2019. The milling process, including hammer mill followed by cyclonic quinoa and buckwheat, resulted in the production of finest particle size that ultimately increased the quality of the bread (Sciarini et al., 2020).

It has also been reported that sourdough fermentation is suitable for decreasing saponins’ level and improving the rheology and sensory attributes (Bolívar-Monsalve et al., 2018). During fermentation, the amino acid, soluble fibers, phenolics, and antioxidant activity were markedly increased in quinoa sourdough, which later improved the bread quality (Rizzello et al., 2016). Fermentation of pseudo-cereals with Lb. plantarum improves the free amino acid content, gamma-aminobutyric acid (GABA), and phenolic compound while decreasing starch hydrolysis (Coda et al., 2010). The sour dough fermented quinoa flour increases the protein, amino acids, dietary fiber content, antioxidant activity, and tenacity and elasticity of pasta, thereby improved its functional and mechanical quality (Lorusso et al., 2017). The sourdough fermentation of amaranth flour using lactic acid bacteria improve the rheology (viscosity and elasticity) (Houben et al., 2010). The buckwheat sourdough increased the amino acid, magnesium, dietary fibers, phenolic while decreasing the phytic acid and tannins content, thereby extending the shelf-life and increasing the overall quality of the bread (Alvarez-Jubete et al., 2010b; Moroni et al., 2012). The muffin prepared by fermented buckwheat flour showed higher content of macro and micronutrients (WronkoWska, 2016).

In a study, Lactobacillus plantarum 299v® was used for the fermentation of quinoa, canihua, and amaranth grains and flours. It was found that the fermentation process increases the phytate degradation and that too higher in the flours than grains. The addition of Lactobacillus plantarum 299v® increased the lactic acid production during fermentation, and increased the pH and endogenous phytase activity. Also, the bioavailability of minerals was increased during fermentation (Castro-Alba et al., 2019).

Applications of Pseudocereals

The advancement on nutritional value and processing methods, various potential applications of pseudocereals in dietary food have been recognized. Pseudocereals are highly nutritious due to its high nutraceutical potential, and are used in gluten-free product development. Moreover, the proteins present in pseudo-cereals are the richest source of essential amino acids useful in the pharmaceutical and food products. Several studies have showed the potential applications of pseudo-cereals in the developing gluten-free and nutrient-rich products, like bread, confectionary items, pasta, biscuits, etc. Gluten-free bread also contains a higher amount of polyphenol compounds, and hence they impart an antioxidative effect. Whole amaranth flour has also been utilized for the production of gluten-free biscuits having higher protein content. The grains of amaranth and quinoa have been widely utilized in making soups, beverages, porridges, sauces, soufflés, and sweets. The leaf of quinoa is considered the best source of protein that can be used in fodder and food and pharmaceutical industries. Also, the bioactive peptides present in pseudo-cereals are used for different purposes like food supplements, functional food ingredients, and nutraceuticals.

Although many products free from gluten are accessible nowadays from the market; however, a greater number of those products have poor quality in terms of nutrients (Mir et al., 2018). In many studies, it has been reported that the levels of vitamin B, proteins, and fibers are low in gluten-free bakery products compared with gluten-containing bakery products (Thakur et al., 2021a). Thus, there is a need to improvise the development of bakery products free from gluten, matching the nutritional composition with gluten-containing products. Niland and Cash (2018) observed and reported that a diet free from gluten helps in the restoration of health and improves quality of people suffering from celiac diseases. As compared to the normal healthy person, the person with celiac disease, herpetiformis, wheat allergies, dermatitis, gluten sensitivity, and gluten ataxia has a lesser fiber intake from the food, and hence should strictly take a gluten-free diet (Thakur et al., 2021b). People suffering from celiac disease have difficulties in searching for gluten-free products in the market due to high prices of food products, poor sensory features, and shortage and unavailability of a variety of foods, which leads to strictly adhere to a gluten-free diet (Alvarez-Jubete et al., 2010b).

Studies have been conducted to improve the quality of gluten-free products using enzymes, emulsifiers, or hydrocolloids. The flour made from pseudo-cereals (quinoa, amaranth, and buckwheat) was used to produce gluten-free bread compared with those produced from potato and rice starch (Alvarez-Jubete et al., 2010b). Pseudo-cereals enhanced the antioxidant activity and increased fiber, protein, iron, calcium, polyphenol, and vitamin E contents of gluten-free bread. Also, nutrient-dense materials derived from pseudo-cereals have increased nutritional composition and also help in bread preparation with good sensory and physical properties (Capriles & Arêas, 2014). Along with some amount of buckwheat flour to rice-based and corn starch-based flour for the preparation of gluten-free products, the antioxidant capacity and nutritional value were increased (Alvarez-Jubete et al., 2010b). Cheese bread, along with the addition of 10% amaranth flour enhances the levels of dietary fiber, proteins, and iron contents of bread. One of the studies reported that the bread produced from the flour of tartary buckwheat was linked with the reduction in rutin during processing, the concentration of quercetin remained stable, and the product showed overall strong antioxidant activity. The consumption of quinoa increased almost 3 times in the last 8 years (FAOSTAT, 2013). Quinoa and amaranth together are rich in copper, iron, zinc, and manganese, and also reported that the content of magnesium and phosphorus may contribute almost 55% of the daily intake of nutrients from food (do Nascimento et al., 2014).

Challenges and Future Outlook

Instead of the various benefits of pseudo-cereals, yet several challenges related to its cultivation, anti-nutrients and inclusion of these crops into modern food system, includes agronomic factors (yield and growth), social (lack of awareness and low esteem), economic (marketing constraints) as well as technological (seeds processing and genetic factors) challenges are existing (Priego-Poyato et al., 2021). One of the reasons that decline the cultivation of crops is poorly characterized agronomic analysis. Besides agronomic challenges, there is a limitation at the genetic level like self-incompatibility that limits trait improvement and breeding. Similarly, flower abortion and seed shattering are other drawbacks in tartary and common buckwheat that limits their production yield. Other factors like limitation in traditional knowledge reduce cultivation and production of pseudo-cereals (Pirzadah & Malik, 2020).

There are many health concerns linked with the intake of dietary proteins derived from pseudo-cereals. Antinutrients present in plant food are naturally produced by plants and further interfere with absorption, digestion, and utilization of nutrients present in the food (Popova & Mihaylova, 2019). Major anti-nutritional components in quinoa are saponins and, mainly responsible for lowering down the mineral absorption. Another class is phytic acid, forming insoluble chelate with magnesium, iron, zinc, or calcium (Pirzadah & Malik, 2020). Furthermore, oxalates are another group of compounds posing the challenge to accept the pseudo cereals as the food as these can cause irritation in the gastrointestinal tract after ingestion. These include maldigestion of proteins (protease and trypsin inhibitors), and carbohydrates (alpha-amylase inhibitors), malabsorption of minerals (oxalates phytates and tannins), autoimmunity and leaky gut (e.g., some saponins and lectins), inflammation, behavioral effects, and gut dysfunction (when converting cereal gliadins to exorphins), and also exert interference with thyroid iodine uptake (goitrogens) (Popova & Mihaylova, 2019). These adverse effects of antinutrients are generally seen in animals when consumed unprocessed proteins from cereal crops. However, they also exerted beneficial health effects. For instance, at a lower level of lectins, phytates, enzyme inhibitors, saponins, and phenolic compounds, there was a reduction in plasma cholesterol, blood glucose, and triglycerides levels. In addition, saponins have a major role in the functioning of the liver and decrease agglutination of platelets. While some saponins, and also protease inhibitors, phytates, phytoestrogens, and lignans, might help in reducing cancer risk (Popova & Mihaylova, 2019).

Additionally, tannins also have antimicrobial effects. To reduce the concentration of antinutrients in pseudo-cereals and their adverse effects, various processing techniques such as fermentation, soaking, gamma irradiation, sprouting (germination), and heating have been adopted (Popova & Mihaylova, 2019). These processing techniques also remove most of the antinutrients like phytates, glucosinolates, erucic acid, and insoluble fiber from canola proteins that further improve and increase the digestibility and bioavailability (Fleddermann et al., 2013).

Technological interventions are required for generating desirable trait including climate-resilient crops with high nutritional composition, through available genetic resources. Studies on agro-morphological (seed shattering, abiotic, biotic stress), nutritional (trait-specific germplasm), yield related traits, post-harvest technologies are required for further utilization of the information in the crop improvement program. Furthermore, these programs should be easily accessible to the marginal farmers as well as the breeders through a common platform. (Rodríguez et al., 2020). Extension activities and awareness programs for dissemination of knowledge on the nutritional superiority of these pseudo cereals should be conducted and popularized. Market potential of the value-added products of these crops should be explored and documented in order to make pseudo cereals more profitable when compared to other cereal crops. Wider choice through varieties in terms of nutrition, low-input, climate-resilient should be offered through access to the seed. Next, sustainability of these activities can be ensured through community seed bank, capacity building, increasing income and livelihood, social acceptability and synergy starting from production till marketing. These crops should get the place in the national food basket through national policies in order to improve the nutritional surveillance. There is a strong need for the international funding so as to explore the hidden potential of these pseudo-cereals to mitigate the hidden hunger.

Conclusions

The research on pseudo-cereals, especially quinoa, buckwheat, and amaranth has been continuously increasing as gluten-free, nutritious, and functional food products. Along with the gluten-free features, pseudo-cereals also contain high-quality proteins, dietary fibers, minerals like calcium and iron, and phenolic compounds. They also showed bio functional activities as antitumor, antioxidant, hypoglycaemic, anti-hypertensive, antimicrobial, and hypolipidemic. Also, clinical trials revealed their effective uses as health and dietary food supplements. In addition, various processing methods such as germination, cooking, soaking, fermentation, popping, etc., helps in enhancing the nutritional value of grains and make processed gluten-free products like bread, pasta, and confectionary food items. However, in the market, there is still limited availability of gluten-free products. Therefore, more research is needed to exploit and search the functionalities of pseudo-cereals and their food products formulations.