Nutraceutical Profile of the Ceylon Spinach (Talinum triangulare)

Abstract

Objective This study appraises the nutraceutical potential of uncooked and cooked Ceylon spinach, the wild leafy vegetable Talinum triangulare occurring in southwest India.

Materials and Methods Proximal properties (moisture, crude protein, total lipids, crude fiber, ash, total carbohydrates, and calorific value), mineral contents, amino acid composition, in vitro protein digestibility (IVPD), protein digestibility–corrected amino acid score (PDCAAS), protein efficiency ratios (PERs), and fatty acid methyl esters (FAMEs) were evaluated by following standard protocols.

Results Total lipids, crude fiber, total carbohydrates, and calorific value were higher in cooked than in uncooked samples. Among nine minerals assessed, sodium, magnesium, phosphorous, iron, manganese, and zinc were significantly higher in uncooked samples compared with cooked samples. Lysine, methionine, cystine, tyrosine, alanine, arginine, aspartic acid, glutamic acid, and serine were higher and histidine, isoleucine, leucine, phenylalanine, valine, glycine, and proline were lower in uncooked samples. Cooking improved IVPD, PDCAAS, and PER. Capric and linoleic acids were higher in uncooked samples, while palmitic, 1-pyrrolidinebutanoic, and ɑ-linolenic acid acids were higher in cooked samples. The total unsaturated fatty acids (TUFAs) were higher in cooked samples; however, the total saturated fatty acids (TSFAs) were lower in cooked samples. The ratio of TUFA to TSFA was higher in uncooked than in cooked samples.

Conclusion The protein content of T. triangulare is comparable to those of legume seeds and consists of low fat, high fiber, and high carbohydrates along with increased calorific value. The Na/K (<1) and Ca/P (>1) ratios are favorable to combat blood pressure and prevention of calcium loss, respectively. The indispensable amino acids are comparable to or higher than soybean, wheat, and Food and Agriculture Organization of the United Nations and the World Health Organization (FAO-WHO) standards. Improved IVPD, PDCAAS, and PER in cooked samples of T. triangulare support its nutraceutical potential in human diet to tackle the protein-energy malnutrition and supplement of its flour strengthens the value of fortified foods. The nutraceutical potential has possible roles to combat lifestyle diseases such as obesity, diabetes, cancers, and cardiac ailments.

Keywords

proximal qualities - minerals - amino acids - protein bioavailability - fatty acid methyl esters - lifestyle diseases - leafy vegetable

Introduction

Leafy vegetables serve as a common human diet worldwide, and they are well known for low fat, low calories, high protein, high dietary fibers, essential minerals, and health-promoting bioactive compounds.[1] Besides their taste and flavor, they are also known as precursors of hormones.[2] Owing to their versatile composition, leafy vegetables are beneficial in the maintenance of health and prevention of many lifestyle diseases.[3] Leafy vegetables could be compared to legumes owing to their capability to supply amino acids.[4] [5] [6] [7] Wild leafy vegetables are distributed worldwide, and the Indian subcontinent possesses several such value-added resources used by the local and tribal population. A survey in Hassan District of Karnataka State (India) revealed 45 species of wild leafy vegetables consumed by the rural population as food.[8] Similarly, up to 45 species of underutilized leafy vegetables have been documented from the southern part of Karnataka.[9]

Among the common leafy vegetables, up to 500 species of genus Talinum (family: Portulacaceae) are distributed across the world.[10] [11] [12] Leaves and tender stems of several species of Talinum are well known for their edibility as well as medicinal properties.[12] Talinum triangulare is common in southern India, and it grows throughout the year. Besides its nutritional value, T. triangulare is also known for its value-added functional attributes and many bioactive compounds, which serve as nutraceutical sources to combat many human ailments (e.g., cardiovascular, diabetes, neurodegeneration).[13] [14] [15] The objective of this study is to evaluate the nutraceutical potential of uncooked and cooked T. triangulare collected from the southwest coastal region of India.

Materials and Methods

Vegetable and Processing

Tender leaves and stem of T. triangulare (Jacq.) Willd. (Ceylon spinach or waterleaf) were collected during the rainy season (July 2016) from five locations (∼50 m apart) in Payam (Kasaragod District, Kerala;12°29'N, 75°7'E; [Fig. 1a, b]). Samples were cleaned in the laboratory by removing inflorescence and basal stem, followed by rinsing in running water to remove debris. Each sample was divided into two parts ([Fig. 1c]). The first part was dried in an oven (50–55°C) until moisture content drops below 10%, which served as an uncooked sample. Another part was cooked in a household pressure cooker by adding distilled water (3:1) followed by oven drying, which served as a cooked sample. Dried uncooked and cooked samples were powdered and refrigerated (4°C) for analysis ([Fig. 1d, e]).

Fig. 1 (a) Talinum triangulare grown on lateritic soil in southwestern India; (b) stem, leaves, and inflorescence; (c) harvested tender leaves and stem; (d) uncooked dry flour; (e) cooked dry flour.

Proximal Analysis

The moisture content of leaf flour samples was assessed gravimetrically.[16] Proximal qualities such as crude protein, total lipids, crude fiber, ash, total carbohydrates, and calorific value of samples were evaluated by standard protocols. The crude protein content was assessed by the micro-Kjeldahl method (N × 6.25).[17] The total lipids content was extracted in petroleum ether (60–80°C) using the Soxhlet apparatus according to the Association of Official Agricultural Chemists (AOAC)[16] to evaluate gravimetrically. The crude fiber and ash contents were also determined gravimetrically.[16]

Total carbohydrates were estimated based on the procedure outlined by Sadasivam and Manickam.[18] Samples (100 mg) were taken in boiling tubes and extracted in 2.5N HCl (5 mL) in boiling water bath (3 hours) and cooled to room temperature; then, they were neutralized with solid Na₂CO₃ until effervescence clears. The volume was made up to 10 mL using distilled water and then centrifuged, and the supernatant was analyzed. The test sample (0.2 mL) was made up to 1 mL using distilled water; 5% phenol (1 mL) and 96% H₂SO₄ (5 mL) were added, and the sample was shaken well (10 minutes) and incubated in a water bath (20 minutes); and the absorbance at 490 nm was read using glucose standard to express total carbohydrate in percentage (g/100 g). The calorific value was calculated according to Ekanayake et al.[19]

Mineral Analysis

The mineral composition was assessed by the protocol proposed by Ramamurthy and Kannan.[20] Moisture-free samples were subjected to field-emission scanning electron microscope–energy dispersive spectrometer (SEM-EDS) analysis (FESEM Carl Zeiss, Oxford Instruments) with a voltage of 15 kV. The SEM images and corresponding EDS spectrum generated for samples were dependent on the properties (shape, shell, and size) to express minerals in percentage. The ratio of Na/K and Ca/P was calculated.

Amino Acid Analysis

Protocols by Hofmann et al[21] [22] were employed to analyze the amino acids. The alkali-extracted samples were used for tryptophan analysis and oxidized samples were used for sulfur amino acid analysis. The procedure by Brand et al[23] was followed for the derivatization process of esterification with trifluoroacetylation. Amino acids in reaction vials dried in CH₂Cl₂ served as standards. Samples were hydrolyzed in HCl and evaporated in rotary evaporator (Büchi Laboratoriumstechnik AG RE121) with a diaphragm vacuum pump (MC2C; Vacuubrand GmbH) followed by measurements in GC-C-IRMS/MS. Gas chromatograph (Hewlett-Packard 58590 II) connected through a combustion interface to the IRMS system (GC-C-II to MAT 252, Finnigan MAT) was employed for measurements of GC-C-IRMS/MS for the isotopic determination of nitrogen through a transfer line with a mass spectrometer (GCQ, Finnigan MAT) for determination of the amino acids. The ratio of total essential amino acids (TEAA) to total amino acids (TAA) was calculated (TEAA/TAA).

Protein Quality Assessment

The in vitro protein digestibility (IVPD) was assessed using enzymes (pepsin, trypsin, and α-chymotrypsin) as per the method by Akeson and Stahmann.[24] Samples (100 mg) were treated with pepsin (Sigma, 3,165 units/mg protein; 1.5 mg of pepsin/0.1N HCl [2.5 mL]) at 37°C (3 hours) and inactivated with 1N NaOH (0.25 mL). Again, the samples were incubated by addition of trypsin (Sigma, 16,100 units/mg protein) and α-chymotrypsin (Sigma, 76 units/mg protein; 2 mg each/0.1M potassium phosphate buffer, pH 8.0 [2.5 mL]) at 37°C (24 hours) and further inactivated with 100% trichloroacetic acid (TCA; 0.7 mL). Zero-time control was maintained by inactivation of the enzyme before the addition of samples. The supernatant was collected by centrifugation of inactivated mixture. The residues are washed with 10% TCA (2 mL) and centrifuged. Combined supernatant was pooled twice with diethyl ether (10 mL) and the ether layer was removed by aspiration. Traces of ether in an aqueous layer were eliminated by heating in a boiling water bath (15 minutes). Cooled to room temperature and solution was made up to 25 mL of distilled water. Aliquots (10 mL) were assessed for nitrogen content using the micro-Kjeldahl method[17] to estimate the protein in the digest.

Essential amino acid score (EAAS) was determined according to the Food and Agriculture Organization of the United Nations and the World Health Organization (FAO-WHO)[25] essential amino acids (EAA( requirement pattern for adults.

Protein digestibility–corrected amino acid score (PDCAAS) for adult was calculated based on FAO-WHO.[25]

Protein efficiency ratio (PER) was determined based on the amino acid composition based on Alsmeyer et al.[26]

Fatty Acid Analysis

Total lipids of uncooked and cooked samples extracted by the Soxhlet method were used for the analysis of fatty acid methyl esters (FAMEs).[27] The gas chromatograph (GC-2010, Shimadzu, Japan) combined with an auto-injector (AOI) and capillary column (BPX-70) was used. Elutants were detected on flame ionization detector, and the amplified signals were transferred and monitored using the GC Solutions software (http://www.shimadzu.eu/products/software/labsolutions/gcgcms/default.aspx). Analytical conditions of autosampler, injection port settings, column oven settings, and column information of the gas chromatograph were maintained according to Nareshkumar.[28] The quantity of FAMEs was evaluated based on a comparison of the peaks of spectra and retention time (RT) of peaks, RT and hits of known compounds stocked in the National Institute of Standards and Technology (NIST) library. The ratio of total unsaturated fatty acid (TUFA) to total saturated fatty acid (TSFA) was calculated.

Data Processing

Proximal properties, minerals, amino acids, IVPD, and FAMEs between uncooked and cooked samples were assessed by Student's t-test using Statistica version 8.0.[29]

Results and Discussion

Proximal Qualities

Results of seven proximal features have been represented in [Table 1]. Moisture content in uncooked and cooked samples was approximately 5% and did not vary significantly (p > 0.05). Similar to moisture, crude protein content (30.9–32.8%; p > 0.05) was not significantly altered by cooking. The total lipids, crude fiber, total carbohydrates, and calorific value were increased in cooked samples (p < 0.05), while the ash content was higher in uncooked samples (p < 0.01).

Table 1 Proximal characteristics of uncooked and cooked Talinum triangulare on a dry weight basis (n = 5; mean ± SD)

	Uncooked	Cooked
Moisture (%)	4.83 ± 0.06	5.06 ± 0.1
Crude protein (g/100 g)	30.85 ± 0.12	32.76 ± 1.21
Total lipids (g/100 g)	4.30 ± 0.1	5.64 ± 0.7*
Crude fiber (g/100 g)	14.10 ± 0.15	14.33 ± 0.09*
Ash (g/100 g)	11.88 ± 0.1**	7.08 ± 0.36
Total carbohydrates (g/100 g)	38.17 ± 0.76	40.33 ± 0.58*
Calorific value (kJ/100 g)	1,314.6 ± 16.97	1,433.3 ± 55.31*

Note: Asterisks represent significant differences (t-test: *p < 0.05; **p < 0.01).

The crude protein content of T. triangulare is similar to those in many leafy vegetables as well as legume seeds. Its content in T. triangulare (30.9–32.8%) is comparable to those in wild legumes such as Canavalia cathartica and C. maritima (28–35.5%) occurring in the coastal sand dunes of the southwest coast of India.[30] [31] The crude protein content is almost similar to T. triangulare grown in Nigeria (30.5%).[1] It did not vary between uncooked and cooked samples (30.9 vs 32.8%; p > 0.05) and was comparable with other vegetables such as Amaranthus hybridus (33%), A. incurvatus (31.5%), Asparagus officinalis (32.7%), Brassica oleracea (34.2%), and Telfairia occidentalis (31.2%).[32] [33] [34] [35]

The total lipid of T. triangulare was higher in cooked samples (4.3 vs 5.6%; p < 0.05), which is lower than those in leafy vegetables such as B. oleracea (11.9%), Gnetum africanum (7.1%), Moringa oleifera (9.3%), and T. occidentalis (10%),[32] [35] while the total lipid in uncooked T. triangulare is comparable to that in Cucurbita pepo leaves (4.2%).[32] The low lipid content in T. triangulare is advantageous in the human diet in combating obesity.

Crude fiber increased in cooked samples (14.1 vs 14.3%; p < 0.05). The crude fiber contents in uncooked and cooked samples (14.1 and 14.3%) are high compared with that in T. triangulare grown in Nigeria (8.9%).[1] The crude fiber content might have increased owing to loss of minerals, which has been reflected in the significant loss of ash content. Such variations were also seen in the edible fern Diplazium esculentum.[36] The fiber content in T. triangulare is higher than those in other leafy vegetables such as Amaranthus viridis (11.9%), M. oleifera (9.4%), and T. occidentalis (2.6%),[35] [37] while it is comparable to that in B. oleracea (14%).[35] The high fiber content in T. triangulare is advantageous in the human diet as it helps in the improvement of digestibility (traps fewer proteins and carbohydrates), lowers blood cholesterol, and combats the risks of bowel and colon cancers.[38] [39] [40] The high fiber content is also known to delay the conversion of starch into simple sugars, which helps to control diabetes.[41]

Ash was higher in uncooked samples (11.9 vs 7.1%; p < 0.01), which is more than that found in T. triangulare grown in Nigeria (2.9%).[1] However, the ash content in T. triangulare is lower compared with those in other vegetables (e.g., A. hybridus, A. viridis, C. pepo, and T. occidentalis).[32] [35] [37] The low ash content in cooked samples of T. triangulare has been reflected in the loss of several minerals (see [Table 2]).

Table 2 Mineral composition of uncooked and cooked Talinum triangulare (g/100 g) (n = 5; mean ± SD)

	Uncooked	Cooked	NRC-NAS–recommended pattern[a]		ICMR-recommended values[b]
			Children	Adults	Children	Adults
Na	0.05 ± 0.0005*	0.04 ± 0.0006	0.12–0.4	0.5	0.6–1	1.9–2.1
K	13.24 ± 0.1	12.52 ± 0.59	0.5–1.6	1.6–2	1.1–1.6	3.2–3.8
Ca	1.22 ± 0.01	1.15 ± 0.06	0.6–0.8	0.8	–	–
Mg	1.99 ± 0.02*	1.49 ± 0.08	0.06–0.17	0.28–0.35	–	–
P	0.46 ± 0.006*	0.36 ± 0.02	0.5–0.8	0.8	0.6–0.8	0.6–1.2
Fe	0.44 ± 0.006***	BDL	0.01	0.01–0.015	–	–
Mn	0.17 ± 0.002**	0.06 ± 0.006	0.0003–0.003	0.002–0.005	0.004	0.004
Zn	0.05 ± 0.02***	BDL	0.005–0.01	0.012–0.015	–	–
S	0.58 ± 0.03	0.56 ± 0.006	–	–	–	–
Na/K ratio	0.004	0.003	–	–	–	–
Ca/P ratio	2.63	3.20	–	–	–	–

Abbreviations: BDL, below detectable level; ICMR, Indian Council of Medical Research; NRC-NAS, National Research Council-National Academy of Sciences.

Note: Asterisk represent significant differences (t-test: *p < 0.05; **p < 0.01; ***p< 0.001).

^a NRC-NAS–recommended pattern.[46]

^b ICMR-recommended pattern.[47]

The total carbohydrate content in cooked T. triangulare increases (38.2 vs 40.3%; p < 0.05), but is lower compared with A. viridis (49.5%), Chlorophytum comosum (65.8%), M. oleifera (42.2%), and T. triangulare (55.9%).[1] [34] [35] [37] The carbohydrate content in T. triangulare was also lower than those of leafy vegetables consumed in southern Côte d'Ivoire (42.9–55.6%),[3] but was higher than other vegetables such as A. hybridus (15.4%), A. officinalis (34.7%), B. oleracea (19%), C. pepo (30.4%), G. africanum (30.4%), and T. occidentalis (35%).[32] [34] [35] T. triangulare, both uncooked and cooked, is endowed with an adequate quantity of carbohydrates as a source of energy and is also capable of combating intestinal cancers and type II diabetes.[42]

The calorific value of T. triangulare was higher in cooked than in uncooked samples (1,433 vs 1,315 kJ/100 g; p < 0.05). Cooking T. triangulare does not lower its calorific value as there is no loss of protein, lipids, and carbohydrates.

The proximate values of uncooked samples of T. triangulare found in this study are different from those reported in earlier studies, possibly due to different geographic distribution such as the tropical American region and Nigeria.[43] [44]

Mineral Constituents

Among the nine minerals in T. triangulare, potassium was the most dominant, followed by magnesium and calcium ([Table 2]). Sodium, magnesium, phosphorous (p < 0.01), and manganese (p < 0.001) were higher in uncooked samples than in cooked samples, while potassium, calcium, and sulfur did not vary between uncooked and cooked samples (p > 0.05). Iron and zinc were confined to uncooked samples. Levels of potassium, calcium, magnesium, and phosphorus in uncooked and cooked samples and iron and zinc in uncooked samples were higher than those in T. triangulare grown in Nigeria.[1] Potassium, calcium, and phosphorus are higher, while the sodium content in cooked samples is comparable with Talinum portulacifolium.[11] The potassium content of T. triangulare is higher than those in other vegetables such as Basella alba, B. oleracea, Colocasia esculenta, Corchorus olitorius, M. oleifera, Solanum melongena, and T. occidentalis as well as in some underutilized leafy vegetables in Assam, India.[3] [35] [45]

The potassium, calcium, magnesium, iron, manganese, and zinc contents in T. triangulare are higher than the National Research Council - National Academy of Sciences (NRC-NAS)–recommended pattern for infants/children and adults,[46] while the sodium and phosphorus contents are lower. On the contrary, potassium and manganese are higher, while phosphorus is comparable to and sodium is lower than the Indian Council of Medical Research (ICMR)-recommended pattern.[47] Low sodium and high potassium in T. triangulare lower the Na/K ratio (<1:0.003–0.004), while high calcium and low phosphorus increase the Ca/P ratio (>1:2.6–3.2). The low Na/K ratio (<1) is beneficial in lowering blood pressure as well as hypertension, while the high Ca/P ratio (>1) prevents the loss of calcium through urine and restores calcium in the bones.[48] [49] As calcium is involved in bone development, it also prevents rickets as well as osteoporosis.[1] A considerable amount of magnesium is known to be effective against coronary heart diseases as well as stroke.

Amino Acid Composition

Lysine and leucine were the dominant essential amino acids, while glycine was the dominant nonessential amino acid in T. triangulare ([Table 3]). Lysine, methionine, tyrosine, alanine, arginine, aspartic acid, glutamic acid, serine (p < 0.001), and cystine (p < 0.01) were higher in uncooked samples compared with cooked samples. Isoleucine, leucine, phenylalanine, glycine, proline (p < 0.001), histidine, and valine (p < 0.01) increased in cooked samples. The quantity of isoleucine, leucine, lysine, tyrosine, threonine, valine, alanine, arginine, aspartic acid, glycine, proline, and serine was higher in T. triangulare than in the leafy vegetable A. hybridus, while it was reverse for histidine, cystine, and glutamic acid.[50] Most of the essential amino acids present in T. triangulare surpassed the FAO-WHO–recommended pattern,[25] so also the amino acid composition of soybean and wheat.[51] [52] The quantities of some of the amino acids that increased in cooked samples might be due to interconversion, which has been reflected in the increased TEAA/TAA ratio in cooked samples. These results corroborate with the edible fern Diplazium esculentum.[36]

Table 3 Amino acid composition of uncooked and cooked Talinum triangulare in comparison with soybean, wheat, and FAO-WHO–recommended[25] pattern for adults (g/100 g protein) (n = 5, mean ± SD)

	Uncooked	Cooked	Soybean[a]	Wheat[b]	FAO-WHO[c]
Essential amino acid
Histidine	1.94 ± 0.02	2.06 ± 0.01*	2.50	1.9–2.6	1.90
Isoleucine	5.04 ± 0.006	5.79 ± 0.04**	4.62	3.4–4.1	2.80
Leucine	7.30 ± 0.17	9.96 ± 0.03**	7.72	6.5–7.2	6.60
Lysine	13.04 ± 0.04**	8.87 ± 0.21	6.08	1.8–2.4	5.80
Methionine	2.43 ± 0.01**	1.52 ± 0.02	1.22	0.9–1.5	2.50[d]
Cystine	0.22 ± 0.006*	0.05 ± 0.02	1.70	1.6–2.6
Phenylalanine	3.77 ± 0.04	6.74 ± 0.05**	4.84	4.5–4.9	6.30[e]
Tyrosine	3.68 ± 0.02**	3.21 ± 0.02	1.24	1.8–3.2
Threonine	4.33 ± 0.03	4.32 ± 0.006	3.76	2.2–3.0	3.40
Tryptophan	BDL	BDL	3.39	0.7–1.0	1.10
Valine	5.03 ± 0.12	5.9 ± 0.02*	4.59	3.7–4.5	3.50
Nonessential amino acid
Alanine	7.45 ± 0.02**	6.53 ± 0.06	4.23	2.8–3.0
Arginine	6.19 ± 0.01**	4.75 ± 0.02	7.13	3.1–3.8
Aspartic acid	7.54 ± 0.04**	5.43 ± 0.006	11.30	3.7–4.2
Glutamic acid	9.77 ± 0.06**	6.49 ± 0.006	16.90	35.5–36.9
Glycine	10.86 ± 0.01	13.35 ± 0.03**	4.01	3.2–3.5
Proline	5.40 ± 0.006	9.27 ± 0.06**	4.86	11.4–11.7
Serine	4.57 ± 0.01**	4.20 ± 0.01	5.67	3.7–4.8
TEAA/TAA ratio	0.47	0.48	–	–

Abbreviations: BDL, below detectable level; FAO-WHO, Food and Agriculture Organization of the United Nations and the World Health Organization; TAA, total amino acids; TEAA, total essential amino acids.

Note: Asterisks represent significant differences (t-test: *p < 0.01; **p < 0.001).

^a Bau et al.[51]

^b USDA.[52]

^c FAO-WHO pattern.[25]

^d Methionine + cystine.

^e Phenylalanine + tyrosine.

Protein Bioavailability

Protein digestibility and bioavailability are the major aspects that help determine protein quality in the foodstuffs. The difference in protein digestibility is due to the nature of proteins, which alter the digestion.[7] The plant protein digestibility will be impaired owing to the presence of antinutritional factors (e.g., polyphenols, phytic acid, trypsin inhibitors).[7] [53] The IVPD of T. triangulare improved on cooking (49.7 vs 56%; p < 0.01), which serves as an important index to follow the protein bioavailability ([Table 4]). The IVPD in uncooked and cooked samples of T. triangulare was similar to that of untreated/unblanched and differently treated (boil blanching, steam blanching, and boiling + sodium bicarbonate blanching) leaves of Moringa oleifera (49.6–53.7%).[54] The PDCAASs for histidine, isoleucine, leucine, phenylalanine + tyrosine, threonine, and valine were high in cooked samples, and they were high for lysine and methionine + cystine in uncooked samples. The pattern of PDCAAS in T. triangulare indicates its high protein quality, which has been supported by the EAA score. The PER1–3 ranged from 1.9 to 4 in T. triangulare, which is favorable, as those possessing PER up to 2 or >2 have been designated as high-quality foodstuffs.[55]

Table 4 In vitro protein digestibility (IVPD) (n = 5, mean ± SD), essential amino acid score (EAAS), protein digestibility–corrected amino acid score (PDCAAS), and protein efficiency ratio (PER) of uncooked and cooked Talinum triangulare

	Uncooked	Cooked
IVPD (%)	49.66 ± 1.13	55.96 ± 1.06*
EAAS
Histidine	1.02	1.08
Isoleucine	1.80	2.07
Leucine	1.11	1.51
Lysine	2.25	1.53
Methionine + cysteine	1.06	0.63
Phenylalanine + tyrosine	1.18	1.58
Threonine	1.27	1.27
Valine	1.44	1.69
PDCAAS
Histidine	50.65	60.44
Isoleucine	89.39	115.84
Leucine	55.12	84.50
Lysine	111.74	85.62
Methionine + cysteine	52.64	35.25
Phenylalanine + tyrosine	58.60	88.42
Threonine	63.07	71.07
Valine	71.51	94.57
PER
PER1	2.39	3.42
PER2	2.46	3.72
PER3	1.87	4.02

Abbreviations: EAAS, essential amino acid score; IVPD, in vitro protein digestibility; PDCAAS, protein digestibility–corrected amino acid score; PER, protein efficiency ratio.

Note: Asterisk represents significant difference (t-test: *p < 0.01).

Fatty Acid Composition

The FAMEs of T. triangulare are composed of three saturated and two unsaturated fatty acids ([Table 5]). The uncooked samples were dominated by palmitic acid, while the cooked samples were dominated by palmitic as well as ɑ-linolenic acid. Palmitic acid was higher in cooked samples (p < 0.05). The TSFAs were higher in uncooked samples (p < 0.001), while the TUFAs were higher in cooked samples (p < 0.001). It is likely that some of the saturated fatty acids are converted into unsaturated fatty acids due to cooking. Cooked edible fern Diplazium esculentum also showed significant increase in stearic acid.[36] The palmitic acid content is comparable, while the capric, ɑ-linolenic, and linoleic acids are more than those found in T. triangulare grown in Andhra Pradesh, India.[56] The palmitic acid is higher, while the linoleic acid is comparable to that found in the leaves of Portulaca oleracea.[57] In addition, T. triangulare of southern India is also known to possess α-tocopherol (vitamin E).[56] The TUFA/TSFA ratio increased on cooking (0.5 vs 1.3), which is in favorable range to prevent cardiac diseases.[58]

Table 5 Fatty acid methyl esters (FAMEs) of uncooked and cooked Talinum triangulare by Soxhlet extraction (g/100 g lipid) (n = 5, mean ± SD)

	Uncooked	Cooked
Saturated fatty acid
Palmitic acid	22.67 ± 0.02	22.78 ± 0.02*
Capric acid	7.77 ± 0.006***	BDL
1-Pyrrolidinebutanoic acid	BDL	4.85 ± 0.006***
Unsaturated fatty acid
Linoleic acid	14.96 ± 0.006***	BDL
ɑ-Linolenic acid	BDL	34.43 ± 0.02***
TSFA	30.44 ± 0.01**	27.63 ± 0.02
TUFA	14.96 ± 0.006	34.43 ± 0.02**
TUFA/TSFA ratio	0.49	1.25

Abbreviations: BDL, below detectable level; TSFA, total saturated fatty acid; TUFA, total unsaturated fatty acid.

Note: Asterisks represent significant differences (t-test: *p < 0.05; **p <  0.01; ***p< 0.001).

Conclusion

Leafy vegetables have a significant influence on human nutrition and health owing to their value-added nutraceutical potential. The wild leafy vegetable T. triangulare is one of such vegetables that possesses protein content equivalent to the legume seeds with low fat, high fiber, high carbohydrate, and high calorific value. Some of the minerals fulfil the requirement of children and adults with favorable sodium/potassium and calcium/phosphorus ratios. The indispensable amino acids are comparable or higher than soybean and wheat. Increased levels of IVPD, PDCAAS, PERs, and TUFAs in cooked samples qualify T. triangulare as a suitable human diet to combat protein–energy malnutrition. There are several options to process this leafy vegetable (e.g., blanching, partial boiling, frying, microwave curing) to employ in fortified foods to combat lifestyle diseases without loss of its nutraceutical potential.

Conflict of Interest

None declared.

Acknowledgments

The authors are grateful to Mangalore University and the Department of Biosciences for the facilities to carry out this study. The authors are also thankful to the editor and referees for constructive suggestions to improve the presentation of this manuscript.

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Publication History

Article published online:
27 June 2022