Amaranth: Multipurpose Agroindustrial Crop

Abstract

Amaranthus cruentus L. (varieties: Juana, Aurelia, Elena) and Amaranthus viridis L. (variety: Callaloo) have long been utilized in food products for human consumption in Central and South America. However, there is limited information on the chemical composition of these species’ leaves and grains grown in Puerto Rico. This study aimed to fill this gap by evaluating the nutritional profile of these four amaranth varieties cultivated in Puerto Rico. A compositional analysis was conducted using official methods, focusing on lysine, protein, dietary fiber, and mineral content. The results showed high lysine content in both species. Significant differences (p < 0.05) were found in crude protein levels among the leaves, with Elena (23%) and Aurelia (21%) showing the highest values. While protein content among grains averaged 19%, there were no significant differences between varieties. The analysis of dietary fiber revealed significant differences (p < 0.05) in insoluble dietary fiber (IDF) and total dietary fiber (TDF) for the leaves and in IDF, soluble dietary fiber (SDF), and TDF for the grains. Additionally, calcium, magnesium, and phosphorus concentrations differed significantly (p < 0.05) in the leaves, while iron, potassium, and zinc showed no significant variation. Significant differences were found in the grains for calcium, magnesium, iron, and phosphorus. This research highlights the excellent nutritional value of amaranth leaves and grains grown in Puerto Rico, with Elena and Aurelia having exceptionally high protein content in their leaves.

1. Introduction

Amaranth (grains and leafy vegetables) has different origin and domestication centers. Mesoamerica is considered the origin of the annual seed-cultivated species Amaranthus caudatus (Peru), Amaranthus hypochondriacus (Mexico), and Amaranthus cruentus (Guatemala) [1,2]. Amaranths are either annual or short-lived perennials of approximately 60–80 species [3]. Amaranth is a warm-season annual plant native to the tropics [4].

Grain amaranth is an annual herbaceous plant (C4 dicot) with an erect stem and large, colorful inflorescences. Its C4 photosynthesis pathway and unique anatomical features enhance the plant’s efficiency in utilizing CO₂ across a wide range of temperatures [5]. Additionally, amaranth thrives under high light intensity and moisture-stressed environments, contributing to its broad adaptability across diverse environmental conditions. The species can be further distinguished by its inflorescence type (pistillate flower structures), with diverse colors [6].

Amaranth is gaining worldwide attention due to its high nutritional value, health benefits, and ability to thrive in challenging soil and climate conditions [7]. Despite this, detailed global and country-specific data on amaranth production remain limited. Major producers include China, Russia, Bolivia, Ecuador, and Peru, although varieties like Amaranthus cruentus, Amaranthus blitum, and Amaranthus dubius are also cultivated in Africa, where productivity tends to be lower [8].

Both amaranth grains and leaves have been extensively studied for their nutritional benefits. They offer a unique protein composition, providing essential amino acids and a rich source of fat and dietary fiber [9,10]. Amaranth grains, a highly nutritious pseudocereal with a rich phytochemical profile, promote numerous health benefits and offer protection against chronic conditions such as hypertension, diabetes, cancer, and cardiovascular disorders. At the same time, their bioactive compounds further reduce the risk of these diseases [11,12].

Amaranth’s nutritional value and versatility have led to its global recognition as a multifunctional crop. It enhances savory dishes, sweet cereals, salads, soups, and baked goods like bread and pastries [13]. Its gluten-free flour is also used in bread and pizza dough [14].

Planting conditions and the species itself highly influence the growth parameters and nutrient accumulation of amaranth. Studies have shown that amaranth grown in open fields has better growth and nutrient profiles than greenhouse-grown plants, with differences attributed to environmental and genetic factors [15]. According to The Ecology of Tropical Food Crops [16], tropical climate and soil conditions can significantly enhance the nutritional content of crops due to factors such as high temperatures, abundant sunlight, and prolonged growing seasons, which lead to increased photosynthesis and nutrient accumulation. Additionally, these conditions promote active soil microbial life, which further improves nutrient availability. As a result, tropical crops often contain higher levels of essential vitamins, minerals, and beneficial compounds like antioxidants compared to crops grown in temperate regions. In the case of Puerto Rico, the tropical environment may positively influence the nutritional quality of amaranth species, such as Juana, Elena, Aurelia, and Callaloo, boosting their proximate composition and essential mineral content in both grains and leaves.

In Puerto Rico, there is limited awareness of the potential uses of amaranth leaves and grains for human consumption, and no current production exists. To promote its cultivation and consumption, it is vital to share information about amaranth’s high nutritional value and its suitability as a multipurpose crop for tropical regions.

2. Materials and Methods

2.1. Materials

2.1.1. Initial Seed Increase

Small packets containing 50 seeds each of four amaranth varieties (Callaloo, Juana, Aurelia, and Elena) from Guatemala were used for the initial seed increase. This process occurred in the Alzamora Laboratory greenhouse at the University of Puerto Rico, Mayagüez campus. Three seeds of each variety were sown in 3.75 L pots filled with topsoil (Vertisol of the Fraternidad series) obtained from the Agricultural Experimental Substation of Lajas. This method was consistently used for both seed increase and leaf cultivation.

2.1.2. Leaf Production

A completely randomized design with four replications was employed for the leaf cultivation. Pots were manually irrigated to support germination and seedling emergence, with additional watering and weeding performed as required. Three weeks after planting, young, succulent leaves were harvested. The leaves were then dried in a forced-air oven at 65 °C for 72 h, ground using a Wiley mill with a 1 mm screen, and stored in whirl packs for subsequent laboratory analysis.

2.1.3. Field Planting

Seeds from the initial planting were harvested, dried, and cleaned before being field-planted to increase seed quantities for developing the nutritional profile of these amaranths. The four varieties were sown on a well-prepared seedbed (conventional tillage) at the Agricultural Experiment Substation of Isabela, University of Puerto Rico, located on the northwest coast (17°27′32′ N, 67°02′53′ W). This area experiences an average annual rainfall of 1890 mm and temperatures ranging from 22 °C to 32 °C. The soil type was an Oxisol of the Coto series (very fine, kaolinitic, isohyperthermic, typic Hapludox). Seeds were planted in 2 × 4 m plots in February 2018, using a completely randomized design with four replicates. Plots were irrigated to ensure uniform germination and were kept free of weeds and pests. Harvesting occurred when the plants reached optimal maturity (15 weeks after planting, as shown in Figure 1), and the seeds were dried and ground in a Wiley mill for subsequent analysis.

2.2. Methods

2.2.1. Protein Content

Protein content was determined using two methods:

Nitrogen Combustion: this was conducted with a LECO FP-528 nitrogen/protein analyzer according to the American Association of Cereal Chemists International (AACCI) approved method 46-30.01 [17].

Kjeldahl Method: this utilized Kjeldahl block digestion and steam distillation as per the AACCI approved method 46-11.02 [17].

2.2.2. Amino Acid Profile

According to the Association of Official Analytical Collaboration (AOAC) approved method 982.30, the amino acid profile was determined using ion-exchange high-performance chromatography [18].

2.2.3. Total Crude Fat Content

Total crude fat content was measured using Soxhlet extraction with hexane as a solvent, following AOAC method 920.39 [18].

2.2.4. Mineral Content

Macro and micromineral content were determined using the dry ash method to obtain a mineral residue. This residue was dissolved in acid, and the mineral concentrations were analyzed using Inductively Coupled Plasma (ICP) Emission Spectroscopy (Pekin-Elmer, ICP-AES, Waltham, MA, USA), which measures mineral content by detecting light emitted from ionized samples.

2.2.5. Total Starch Content

Total starch was assessed using a total starch assay kit from Megazyme (Megazyme, Ltd. Intl., Bray, Ireland) following the AACCI approved method 76-13.01 [17].

2.2.6. Dietary Fiber Content

Dietary fiber content was determined according to AACCI approved method 32-07.01 [16] using an Ankom automated dietary fiber analyzer (Ankom Technology, New York, NY, USA).

2.3. Statistical Analysis

The experiment followed a completely randomized design (CRD) with a single factor consisting of four levels (Juana, Aurelia, Elena, and Callaloo) and four replications, with samples harvested at two growth stages (leaves and grains). Data were analyzed using analysis of variance (ANOVA) at a significance level of p < 0.05, and mean separation was performed using Tukey’s test, with SAS version 9.4 software.

3. Results and Discussion

3.1. Protein Content in Amaranth Leaves and Grains by Two Nitrogen Analytical Methods (Kjeldahl and Combustion)

No significant interaction (p > 0.05) was observed between amaranth varieties in the nitrogen (N) determination procedure for crude protein content in both leaves and grains. There was no interaction (p > 0.05) between amaranth varieties by the N (nitrogen) determination procedure for crude protein in leaves and grains. There was, however, a significant (p > 0.05) difference between N determination procedure (Kjeldahl versus Combustion) and among amaranth varieties (leaves only,

Table 1. Effects of N procedures (Kjeldahl and Combustion) on crude protein percentage in leaves and grains of four amaranth varieties.

Variety	Leaves		Grains
	Kjeldahl	Combustion	Kjeldahl	Combustion
	% (DWB)	% (DWB)	% (DWB)	% (DWB)
Juana	18.06 b	20.11 a	15.87 b	21.64 a
Elena	21.99 b	23.41 a	17.62 b	20.02 a
Callaloo	18.91 b	20.11 a	15.67 b	16.93 a
Aurelia	20.09 b	21.58 a	17.92 b	17.72 a

DWB = dry weight basis. Means followed by different letters in the same row are significantly different by Tukey’s test, n = 4.

). Table 1 presents crude protein mean values by N procedures, showing higher protein for both leaves and grains by the Combustion method.

Ngugi et al. [19] and Stevanović et al. [20] report that the protein content in amaranth leaves generally ranges from 17% to 20%. Consistent with these findings, this study shows crude protein levels of 19.76% using the Kjeldahl method, with combustion analysis yielding a slightly higher value of 21.30%. Another study by Andini et al. [21] evaluating the protein variation in leaves of grain, vegetable, and weedy types of amaranths (Amaranthus viridis, Amaranthus blitum L., and Amaranthus dubius) reported 12 to 29% protein. This study was in the range of Elena (22.70%) and Aurelia (20.84%), presenting higher protein values compared to 19.51% and 19.05% for Callaloo and Juana, respectively.

The nutritional value of leafy amaranth is similar to or higher than common vegetables (e.g., spinach). The nutritional composition of dehydrated spinach was evaluated [22] and reported 8.2% of protein, a lower percentage than the amaranth varieties studied in this research (Table 1).

Valcárcel-Yamani and Lannes [23], Gelaye [9], and the U.S. Department of Agriculture Agricultural Research Service [24] have reported that amaranth grains contain between 14% and 21% protein. The results of this study align with these findings (Table 1). In comparison, traditional cereals like maize (10.5%), sorghum (12.4%), and wheat (14.8%) have lower protein contents [1].

3.2. Amino Acids Profile in Amaranth Grains

Pooled samples (four replications) were used to develop an amino acids profile of amaranth varieties (Juana, Elena, Callaloo, and Aurelia).

Table 2. Essential amino acids content for amaranth grain in the four varieties.

Amino Acids	Juana	Elena	Callaloo	Aurelia	Mean of Varieties
	g/100 g (DWB)
Threonine	0.69	0.62	0.56	0.56	0.61
Valine	0.84	0.77	0.66	0.67	0.74
Methionine	0.42	0.36	0.32	0.33	0.36
Isoleucine	0.75	0.71	0.62	0.61	0.67
Leucine	1.11	1.04	0.90	0.90	0.99
Phenylalanine	0.84	0.78	0.67	0.68	0.74
Lysine	1.14	1.02	0.92	0.93	1.00
Histidine	0.51	0.49	0.43	0.43	0.47
Tryptophan	0.28	0.28	0.23	0.22	0.25
Total	6.58	6.07	5.31	5.33	5.82

DWB = dry weight basis, n = 1.

and

Table 3. Nonessential amino acids content for amaranth grains in the four varieties.

Amino Acid	Juana	Elena	Callaloo	Aurelia	Mean of Varieties
	g/100 g (Dry Weight Basis)
Taurine	0.01	0.03	0.02	0.02	0.02
Hydroxyproline	0.11	0.12	0.09	0.09	0.10
Aspartic Acid	1.58	1.48	1.29	1.3	1.41
Serine	1.00	0.94	0.85	0.85	0.91
Glutamic Acid	3.24	2.87	2.62	2.64	2.84
Proline	0.79	0.73	0.67	0.65	0.71
Lanthionine	0.00	0.00	0.00	0.00	0.00
Glycine	1.52	1.36	1.25	1.28	1.35
Alanine	0.74	0.68	0.59	0.6	0.65
Cysteine	0.49	0.4	0.38	0.37	0.41
Tyrosine	0.66	0.58	0.51	0.52	0.57
Hydroxylysine	0.02	0.02	0.02	0.02	0.02
Arginine	1.78	1.60	1.42	1.45	1.56
Ornithine	0.01	0.02	0.01	0.01	0.01
Total	11.95	10.83	9.72	9.80	10.58

DWB = dry weight basis, n = 1.

present essential and nonessential amino acids expressed in g/100 g of grain (dry weight basis).

Amaranth grains have a high protein content, great bioavailability, and a well-balanced amino acid profile [25,26]. The amino acids profile obtained in this study agrees with those of Palombini et al. [27], Szabóová [28], and Procopet [29]. Amaranth presented a higher lysine content (1.00 g/100 g), which is the more limiting amino acid in traditional cereals such as maize (0.27 g/100 g), rice (0.24 g/100 g), and wheat (0.36 g/100 g), as well as in vegetable proteins [24].

The essential amino acids are expressed in g/100 g of amaranth grains. Leucine (0.99), lysine (1.00), phenylalanine (0.74), and valine (0.74) presented higher concentrations. These results are slightly higher than those reported by Palombini et al. [27] and the U.S. Department of Agriculture-Agricultural Research Service [24], with values for leucine, lysine, phenylalanine, and valine, ranging from 0.86 to 0.88, 0.75 to 0.83, 0.56 to 0.61, 0.57 to 0.67, respectively.

3.3. Dietary Fiber Content in Amaranth Leaves and Grains

There were significant differences (p > 0.05) in insoluble dietary fiber (IDF) and total dietary fiber (TDF) among the amaranth varieties, while soluble dietary fiber (SDF) showed no significant variation. Aurelia exhibited an IDF percentage that was nine units higher than Callaloo and five units higher than both Juana and Elena. These differences were also reflected in the TDF percentages, though the SDF values remained consistent across varieties, averaging 5.80% (

Table 4. Percentage insoluble (IDF), soluble (SDF), and total (TDF) dietary fiber in leaves of amaranth varieties.

Variety	Insoluble Dietary Fiber (%, DWB)	Soluble Dietary Fiber (%, DWB)	Total Dietary Fiber (%, DWB)
Juana	26.85 b	5.78 a	32.63 b
Elena	27.18 b	5.85 a	33.03 b
Callaloo	22.95 c	5.48 a	28.43 c
Aurelia	32.08 a	6.10 a	38.18 a

DWB = dry weight basis. Means in the same column followed by the same letter are not significantly different by Tukey’s test, n = 4.

). Notably, the TDF levels in amaranth leaves were higher compared to the grains, with Aurelia standing out for its superior dietary fiber content, showing 32.08% IDF and 38.18% TDF in the leaves.

Table 5. Percentage insoluble (IDF), soluble (SDF), and total (TDF) dietary fiber in grains of amaranth varieties.

Variety	Insoluble Dietary Fiber (%, DWB)	Soluble Dietary Fiber (%, DWB)	Total Dietary Fiber (%, DWB)
Juana	11.20 a	5.35 b	16.55 a
Aurelia	10.73 a	6.25 a	16.98 a
Elena	9.93 b	4.75 b	14.68 b
Callaloo	7.95 c	4.75 b	12.70 c

DWB = dry weight basis. Means in the same column followed by the same letter are not significantly different (p > 0.05), n = 4.

shows the percentages of insoluble dietary fiber (IDF), soluble dietary fiber (SDF), and total dietary fiber (TDF) in grains of the four amaranth varieties. Juana and Aurelia had IDF percentages that were three units higher than Callaloo and one unit higher than Elena. This trend is also evident in the TDF percentages, with Juana and Aurelia being four and two units higher than Callaloo and Elena, respectively. Among Juana, Elena, and Callaloo, the SDF levels were similar at 4.95%, whereas Aurelia had a higher SDF percentage at 6.25%.

The percentage of dietary fiber in amaranth grains was reported to be 12.0 to 20.6% [30]. The values found in this study (12.70 to 16.78%) are within that range. Lower dietary fiber percentages (8.8%) have been reported by Filho, Pirozi, Borges, Pinheiro Sant’Ana, Chaves, and Coimbra [1]. Another author reported the IDF, SDF, and TDF to be 6.56, 4.56, and 11.15%, respectively [31]. These values are much lower than those found in this study. Amaranth grains are considered a good source of insoluble fiber, but it should be noted that the percentage of dietary fiber depends on the variety evaluated.

3.4. Total Fat and Total Starch in Four Amaranth Grain Varieties

There was no significant difference (p > 0.05) for fat and total starch among the amaranth varieties Juana, Elena, Callaloo, and Aurelia (

Table 6. Total fat and total starch contents of grains of four amaranth varieties.

Variety	Fat (%, DWB)	Starch (%, DWB)
Juana	7.03 a	49.17 a
Elena	6.35 a	52.69 a
Callaloo	6.71 a	56.87 a
Aurelia	6.85 a	56.74 a

DWB = dry weight basis. Means in the same column followed by the same letter are not significantly different (p > 0.05), n = 4.

).

The average total fat content across the amaranth varieties was 6.74%. This is consistent with findings from Palombini et al. [27], who reported a content of 6.43%. Sattar et al. [32] and Baraniak et al. [33] reported a range of 6.04% to 7.7%, aligning with the range found in this study. In contrast, Nascimento et al. [34] reported a higher total fat value of 10.9%. Compared to other grains, amaranth contains more fat per 100 g dry weight: beans (1.1 g), maize (4.7 g), rice (2.2 g), and wheat (2.3 g) [29]. Total fat also depends on species or genotype and can vary from 1.9 to 9.7% [35].

The average total starch content was 53% among the amaranth varieties. Alonso-Miravalles and O’Mahony [36] reported a content of 52.8%, while Venskutonis and Kraujalis [2] noted values ranging from 40% to 52%, like those observed in this study. However, Nascimento et al. [34] and the U.S. Department of Agriculture Agricultural Research Service [24] reported higher total starch values ranging from 55.30% to 57.27%. Starch is the main component of amaranth grain, comprising about 48% to 69% of the total grain content [35], which aligns with the range observed in this study. This starch content is comparable to that of other cereals, such as barley (61.4%), rye (57.1%), and oats (62.1%) [37].

3.5. Mineral Concentration in Amaranth Leaves and Grains

The mineral composition of amaranth is essential for assessing its nutritional value. Significant differences (p < 0.05) were found in the calcium (Ca), magnesium (Mg), and phosphorus (P) content of amaranth leaves. At the same time, potassium (K), iron (Fe), and zinc (Zn) showed no significant variation (p > 0.05). Significant differences (p < 0.05) were observed in amaranth grains for Ca, Mg, P, K, and Fe, but not for Zn. Specifically, Juana had a higher Ca concentration than Elena, while Callaloo and Aurelia were comparable. Juana and Elena also exhibited higher levels of Mg (1.41%), P (0.95%), and K (4.4%) than Callaloo and Aurelia. The Fe content (14.72 mg/100 g) and Zn (21.65 mg/100 g) were notably higher in Juana and Elena compared to Callaloo and Aurelia (6.11 mg/100 g) (

Table 7. Mineral concentration in leaves of four amaranth varieties.

	Ca	Mg	P	K	Fe	Zn
Variety	% (DWB) mg/100 g
Juana	2.67 a	1.43 a	0.99 a	4.37 a	10.95 a	9.13 a
Elena	2.35 b	1.40 a	0.91 a	4.54 a	12.56 a	9.40 a
Callaloo	1.57 c	1.13 b	0.51 b	3.90 ab	16.96 a	6.23 b
Aurelia	1.41 c	1.00 c	0.62 b	3.20 b	18.42 a	5.99 b

DWB = dry weight basis. Means followed by different letters in the same column are significantly different by Tukey’s test, n = 4.

).

Amaranth leaves are an excellent source of minerals, including iron. According to the National Institutes of Health, the average daily iron intake from foods is 11.5–13.7 mg/day for children aged 2–11 years, 15.1 mg/day for teens aged 12–19 years, and 16.3–18.2 mg/day for men and 12.6–13.5 mg/day for women over 19 years old [38]. These iron requirements can be met by incorporating amaranth leaves into the diet, a more affordable alternative than many common vegetables. Nascimento et al. [34] reported iron values ranging from 12.23 to 14.55 mg/100 g, consistent with this study.

For amaranth grains, the calcium content was similar across Callaloo, Aurelia, and Juana, each at 0.20%. However, Aurelia, Juana, and Elena had comparable calcium percentages. Magnesium levels were higher in Aurelia, Juana, and Callaloo (1.42%) than Elena, which had a similar value to Callaloo (0.23%). Phosphorus percentages were similar among Juana, Callaloo, and Aurelia, while Elena had a lower rate (0.35%). The potassium content was highest in Callaloo and Juana (52%), surpassing that in Elena and Aurelia. Callaloo also had the highest iron concentration (98.39 mg/100 g), while Aurelia, Elena, and Juana had lower averages (28.23 mg/100 g). Zinc concentrations averaged 6.18 mg/100 g across the different amaranth varieties (

Table 8. Mineral concentration in grains of Juana, Elena, Callaloo, and Aurelia.

	Ca	Mg	P	K	Fe	Zn
Amaranth Varieties	% (DWB) mg/100 g
Juana	0.18 ab	0.26 a	0.49 a	0.51 ab	38.24 b	6.86 a
Elena	0.16 b	0.20 b	0.35 b	0.37 c	20.34 b	5.83 a
Callaloo	0.21 a	0.25 ab	0.45 ab	0.54 a	98.39 a	5.91 a
Aurelia	0.20 ab	0.26 a	0.45 ab	0.41 bc	26.12 b	6.10 a

DWB = dry weight basis. Means followed by different letters in the same column are significantly different by Tukey’s test, n = 4.

).

Olusanya et al. [39] reported Fe concentration of 3.59 to 10.81 mg/100 g in Amaranthus dubius, while Chege et al. [40] found 5.75 mg/100 g in Amaranthus cruentus leaves. The iron concentrations in both leaves and grains in this study are much higher than those reported by other researchers.

Amaranth stands out for its high concentrations of iron, magnesium, and zinc, positioning it as a significant source of these essential minerals in relation to daily nutritional recommendations [41]. Compared to other cereals, amaranth demonstrates superior mineral content, with iron levels surpassing those in maize (2.7 mg/100 g), rice (1.2 mg/100 g), and wheat (3.7 mg/100 g), and zinc levels higher than in maize (2.2 mg/100 g), rice (0.6 mg/100 g), and wheat (3.6 mg/100 g) [24]. Gluten-free products are often deficient in key minerals such as calcium, magnesium, and iron, making amaranth a particularly valuable nutrient source for individuals with celiac disease [42]. Variations in mineral content observed across studies may be attributed to differences in genotypes, soil conditions, and fertilizer practices [7].

4. Conclusions

This study provides essential information and a basic characterization of the chemical composition of the grain-type amaranths Juana, Elena, and Aurelia and the leafy-type Callaloo. The results demonstrate that amaranths are an excellent source of nutrients, containing a balanced set of amino acids in both the leaves and grains. Lysine, an amino acid often limited in cereals, is significantly higher in amaranths. Additionally, protein percentages in the leaves of Elena and Aurelia were notably higher (by 3 percentage units) compared to the leafy Callaloo. At the same time, the grains averaged 19% protein, much higher than any cereal grain.

Amaranth, a crop with deep historical significance, has been cultivated by cultures such as the Incas, Mayans, and Aztecs. Today, it remains an essential staple in regions like Mexico, Kenya, India, and Peru, where varieties like Amaranthus cruentus and Amaranthus hypochondriacus are grown commercially. The global significance of amaranth as a source of nutrients high in protein, fiber, and minerals like calcium and iron extends its importance beyond Puerto Rico. This study aligns with global findings, demonstrating that amaranth is a nutritious crop and a potential solution for food security in various environments.

Future research should focus on exploring grain production under diverse environmental conditions, such as drought and saline soils, in Puerto Rico. Additionally, processing methods and their impact on amaranth’s nutritional value require further investigation. Sensory evaluation at different growth stages (for leaves) and grains produced across different years and locations will be crucial for understanding how these factors influence the sensory and culinary attributes of amaranth. Finally, research into consumer acceptance and culinary applications will help promote the wider use of amaranth as a staple food around the world.