Edible Leafy Plants from Mexico as Sources of Antioxidant Compounds, and Their Nutritional, Nutraceutical and Antimicrobial Potential: A Review

A review of indigenous Mexican plants with edible stems and leaves and their nutritional and nutraceutical potential was conducted, complemented by the authors’ experiences. In Mexico, more than 250 species with edible stems, leaves, vines and flowers, known as “quelites,” are collected or are cultivated and consumed. The assessment of the quelite composition depends on the chemical characteristics of the compounds being evaluated; the protein quality is a direct function of the amino acid content, which is evaluated by high-performance liquid chromatography (HPLC), and the contribution of minerals is evaluated by atomic absorption spectrometry, inductively coupled plasma-optical emission spectrometry (ICP-OES) or ICP mass spectrometry. The total contents of phenols, flavonoids, carotenoids, saponins and other general compounds have been analyzed using UV-vis spectrophotometry and by HPLC. For the determination of specific compounds such as phenolic compounds, flavonoids, organic acids and other profiles, it is recommended to use HPLC-DAD, UHPLC-DAD, UFLC-PDA or gas chromatography-mass spectrometry. The current biochemical analysis and biological evaluations were performed to understand the mechanisms of action that lead to decreased glucose levels and lipid peroxidation, increased hypoglycemic and antitumor activity, immune system improvement, increased antibacterial and antifungal activity and, in some cases, anti-Helicobacter pylori activity.


Introduction
Diets in all countries are essentially based on the production of a few cultivated species-corn, rice, wheat, potato, soybean, barley, various vegetable species, yuca, beet, tomato, banana and watermelon-and nearly 160 edible species with worldwide distribution have been recorded [1]. The predominance of a few cultivated species and products in the market leads to increased dietary homogeneity; there is a direct relationship between a high diversity of natural edible products in supply systems and dietary variety, which influences the nutritional quality of the diet and affects the health

Diversity and Consumption of Quelites from Mexico
In Mexico, the word "quelite," derived from the indigenous Nahuatl word "quilitl," is used to group all herbaceous, woody, creeping or shrubby plants with or without edible flowers, leaves, vines and stems, regardless of whether they are unprocessed (fresh) or processed. These plants represent a fraction of the biodiversity of plants used as food, which includes grains, fruits, seeds, oilseeds, roots, tubers and other edible structures. Based on floristic and ethnobotanical lists, Mapes and Basurto [17] estimated that in Mexico, there are more than 250 wild, semicultivated and cultivated quelite species that grow in natural areas, are tolerated in crop fields, are on the borders of plots or home gardens or are cultivated for marketing. The main families include the Leguminosae, Asteraceae, Begoniaceae, Brassicaceae, Solanaceae, Piperaceae, Euphorbiaceae, Cucurbitaceae, Amaranthaceae, Convolvulaceae, Chenopodiaceae and 30 others (Table 1). However, fewer than 10 crop species occupy 12.6 million hectares cultivated in Mexico, constituting 85% of the total cultivated area [1] and reflecting a global pattern that is repeated from country to country. This indicates that the diversity of food species is underutilized, a fact that influences dietary diversity and nutritional quality with consequences such as nutritional deficiencies that arise because the main crops are essentially grain and cereal crops, not vegetable crops. Increasing dietary diversity with the consumption of a greater number of species has been proposed as an effective and sustainable strategy to eradicate micronutrient deficiency problems and malnutrition problems associated with overweight and diabetes due to the high intake of fats and ultraprocessed foods and to facilitate access to food, all through the increased consumption of quelites or traditional local vegetables [6,11,24].
Species of quelites or plants with edible stems, leaves, vines and flowers are distributed globally, and in Mexico, they are found in natural and disturbed environments, grazing areas, all agrosystems, parks and protected natural areas. They are widely used in the territories of indigenous communities, where a great number of previously unknown edible species have been recognized, although their consumption is diffused locally or regionally, and they are sold only in local and regional markets where residents are likely to recognize and use them. There is a direct relationship between local knowledge of species and how they are consumed, even when there are cultural transformations of consumption and environmental or anthropogenic changes that shift the distribution or cause the extinction of species [25]. Species of quelites are distributed in practically all eco-and agrosystems in Mexico, from the northern desert [26] to the humid tropical regions of the southern portion [27]. This fact is evident in different ethnobotanical studies that list edible plant species, although the number of species varies from site to site depending on the biogeographic context, the ecosystem, the agrosystem and the specific objectives of each study; however, together, such studies indicate the number of food species that can be considered to be members of the group of quelites. For example, in Candelaria Loxicha, Oaxaca, 73 food species were recorded, and only 16 were quelites in Sierra Norte de Puebla, 94 species were recorded, and 80 were quelites. Consequently, the number of recorded quelite species continues to increase ( Table 2). Collective findings indicate that there are more than 250 species of quelites, as indicated by Mapes and Basurto [17], and this number can be estimated by considering the presence of three or four species per genus, multiplied by 84 genera, as listed in Table 1.   [37] 1 Species number with edible stems, leaves and/or flowers and ns = not specified.

Composition of Edible Stems, Leaves and Flowers of Quelites from Mexico
In all indigenous and rural communities in different countries, knowledge about the consumption of wild or recently domesticated plants is among the strategies for survival and adaptation to environmental conditions. In this and other studies, efforts have been made to assess traditional local and indigenous diets through the documentation of the use of food plants with local or regional distribution, which are unknown at the national and international levels; these evaluations are based on the composition of the edible portion and its contribution to human health [7,38,39]. An additional value of traditional diets is the contribution of foods that have a variety of flavors, colors, aromas and forms of preparation with a low number of additional inputs; for example, traditional foods are often consumed directly in fresh form or with minimal processing.
In the present review, it was determined that protein quality is a function of essential amino acids in reference to the quelite species listed in Table 1. For example, when studying Amaranthus hybridus, Akubugwo et al. [55] discovered relevant concentrations of histidine, alanine, arginine, aspartic acid, glutamic acid, glycine, proline, serine, isoleucine, leucine, lysine, methionine, cysteine, phenylalanine, tyrosine, threonine and valine. Bressani [56] quantified different contents of valine, threonine, isoleucine, leucine, lysine, histidine and arginine in Crotalaria longirostrata. In these two cases, A. hybridus and C. longirostrata have six essential amino acids in concentrations that vary from 1.76 to 6.7 g/100 g protein and contain histidine, which is indispensable for children and pregnant women. From a rural community perspective, these edible plants are locally available, inexpensive protein and amino acid sources. However, it is necessary to not solely evaluate plants from Mexico [7,15].
Phenolic compounds, flavonoids, betacyanins and chlorophyll are some of the compounds responsible for antioxidant activity in quelites. Román-Cortés et al. [53] detected a significant positive correlation between total phenolic compounds and flavonoids with respect to antioxidant activity determined by ABTS, DPPH and DPMD methods. Using FRAP and ORAC, Li et al. [48] also found correlations between total phenolic compounds, total flavonoids and total betalains, and Sarker et al. [68] found correlations between total phenolic compounds, flavonoids, carotenoids, betacyanin, betaxanthin, betalain and chlorophyll via DPPH and ABTS. Although these tests estimate the groups of molecules present, they provide information on their activity or the synergism between them. However, the antioxidant activity in these types of plant can vary according to the genus [53], species [49] and accession within each species [68][69][70]. The results can also differ in each part of the plant; for example, in Amaranthus spp., antioxidant activity (FRAP and ORAC) is different in the seeds, stems, leaves, flowers and shoots, with the highest values found in leaves and the lowest in the seeds [48].
It should be noted that the most consumed quelites in rural populations, such as 'huauzontles' (Chenopodium nuttalliae), 'quelites' (Chenopodium album), 'quintoniles' (Amaranthus hypochondriacus), 'romeritos' (Suaeda calceoliformis) and´verdolagas' (Portulaca oleracea), have higher antioxidant activity (ABTS, DMPD and DPPH) than commercial leafy vegetables such as lettuce (Lactuca sativa) and spinach (Spinacia oleracea) [53]. Similarly, in accessions of Gynandropsis gynandra, Cnidoscolus aconitifolius, Solanum scabrum and Crotalaria, antioxidant activity (ORAC) was higher than in these vegetables [49,71]. Additionally, Jiménez-Aguilar [69] determined that Amaranthus spp. antioxidant activity (ORAC) was higher than that in those vegetable species [49,71]. This suggests that quelites may be an important source of potential antioxidant phytochemical compounds with health effects. It is evident that by including quelites in the diet, their contribution of bioactive compounds would be transcendental in populations with greater problems of malnutrition and health caused by poor eating habits in recent times.

Methods and Techniques for the Determination of Compounds
Assessing the compositions of leaves, stems and flowers of quelite species preponderantly depends on the compound characteristics. For example, in the evaluation of micro-and macrominerals, it is convenient to use atomic absorption spectrophotometry (AAS), inductively coupled plasma-optical spectrometry (ICP-OES) and ICP-mass spectrometry (ICP-MS), where the last two techniques offer major capacity to detect trace elements or very low concentrations [15,54,55,68]. The determination of amino acid contents by high-performance liquid chromatography (HPLC) is a feasible option when the objective is to compare samples or species and protein quality. UV-vis spectrophotometry is a frequent strategy to estimate the total phenols, flavonoids, carotenoids and other compounds based on standards of reference, but when the aim is to elucidate compound profiles or specific compounds, it is pertinent to apply HPLC with diode array detection (HPLC-DAD) and mass spectrometry detection, ultrahigh-performance liquid chromatography with diode array detection (UHPLC-DAD) or gas chromatography-mass spectrometry (GC-MS), Table 4. Piper auritum Leaves β-Pinene, α-terpinene, trans-β-ocimene, terpinolene, safrole, β-caryophyllene, germacrene D, trans-nerolidol and phytol ABTS [52]

Antioxidant Compounds and Health
Quelites or edible leafy plants have the potential to prevent and reduce the incidence of diseases caused by oxidative stress, such as metabolic syndrome, diabetes, cancer and gastrointestinal and neurological diseases, among other diet-associated disorders [60,70,76]. Experiments have been performed to evaluate the nutraceutical potential of edible leafy plants or quelites.

Diabetes
Juárez-Reyes et al. [76] found that extracts of Anoda cristata leaves decrease glucose levels in hyperglycemic mice and that they have a positive effect on serum glucose, triglycerides and the uric acid content in mice with fructose-induced metabolic syndrome. The authors noted that the hypoglycemic effect and antioxidant activity of A. cristata are associated with acacetin and diosmetin. Thus, consumption of A. cristata is suggested to help reduce the risk of type 2 diabetes and cardiovascular diseases.
Aqueous extracts of leaves of Portulaca oleracea generate a decrease in serum glucose levels in diabetic mice. This effect is attributed to the increased insulin secretion in β-cells resulting from the improvement in the transport of glucose to peripheral tissues. Consequently, P. oleracea extract helps to prevent necrosis and atrophy of pancreatic tissue and increases blood circulation by opening blood vessels. Additionally, it reduces the levels of the proinflammatory cytokines TNF-α and IL-6, which are related to the pathogenesis of insulin resistance [77,78].
Methanolic extracts of Cnidoscolus chayamansa at concentrations of 70 mg/kg reduce the blood glucose concentration in mice with induced diabetes. The extracts act by stimulating functional pancreatic β-cells [79]. In this sense, aqueous extracts (2% w/v) of C. chayamansa show hypoglycemic activity in diabetic mice by inhibiting glucose absorption or improving sensitivity to insulin [73]. The effects of these extracts are related to the content of quercetin and catechin and are proposed to act as inhibitors of glucose absorption in intestinal cells [80]. Additionally, C. chayamansa extracts inhibited the growth of mutagenic cancer cells by 24% and 39% compared to that of sodium azide (NaN 3 ) and 4-nitro-O-phenylenediamine (4-N-O-P) controls, respectively [75]; furthermore, the same extracts decreased low-density lipoproteins [LDLs] by 32% and triglycerides by 50% and consequently decreased hyperlipidemia [76].

Cancer
Barros et al. [75] pointed out that plants/young shoots of Chenopodium ambrosioides have high antioxidant activity attributed to their bioactive molecules, and the experimental results of antitumor activity by the use of infusion and methanolic extracts inhibited growth by 50% (GI 50 ) in human cell lines (MCF-7, NCI-H460, HCT-15, HeLa, HepG2) at concentrations from 287.4 to > 400 µg/mL). The consumption of Cnidoscolus aconitifolius induces a protective effect against premalignant lesions (cancer) of the colon in rats by inhibiting cell proliferation and inflammation of colon lesions through a reduction in β-catenin and cyclooxygenase 2 (COX-2) activity [81]. Additionally, extracts of polysaccharides from Portulaca oleracea reduce sarcoma 180 transplanted into mice and have a mitogenic or comitogenic effects on splenocytes in mice with sarcomas by stimulating the proliferation of spleen lymphocytes, an immune response that improves immunity. In another experiment, it was demonstrated that these plant extracts can activate T cells to exert an immunomodulatory effect on tumors in mice [82]. In this respect, Amaranthus cruentus extracts inhibit tumor growth in colon cancer via cytotoxic activity related to the content of rutin, an antioxidant molecule that induces apoptosis and cell cycle arrest [83,84].
Jia-liang et al. [85] indicated that Chenopodium ambrosioides has anticancer activity based on the evaluation of an essential oil that inhibits the proliferation of breast cancer cells (MCF-7) and can be cytotoxic depending on the concentration and time of exposure. For these reasons, a minimum IC 50 of 24 h is proposed. Essential oil of C. ambrosioides causes morphological alterations, membrane blebbing and chromatin condensation, which are typical characteristics of the apoptotic process, and induces DNA fragmentation in cancer cells, reducing the survival of malignant cells [86]. C. ambrosioides leaf extracts induce macrophage activation and phagocytic activity, increase cell recruitment and/or proliferation in secondary lymphoid organs (spleen, lymph node), induce positive immunomodulation in the body and induce nitric oxide (NO) production; together, these effects improve the immune system [87]. In addition, the evaluation of methanolic extracts of the inflorescences and leaves of C. ambrosioides determined that the extracts' antitumor effects against colon, cervical and hepatocellular cancer in vitro is attributable to the content of flavonoids and phenolic acids, which are bioactive molecules with antioxidant capacity that counteract oxidative stress [75].

Obesity and Gastrointestinal Disorder
The ethanolic extracts of Polygonum aviculare L. have an anti-obesity effect in mice with induced obesity and fed high-fat diets. These extracts reduce the increase in body weight, increase in adipose tissue, adipocyte size and expression of lipogenic genes (PPARγ, SREBP-1c, aP2 and FAS) and consequently decrease serum levels of triglycerides, leptin and malondialdehyde (MDA) [88]. The variation in MDA levels indicates a decrease in lipid peroxidation, which could be related to the antioxidant properties of quercetin and other phenolic compounds present in the extracts [88,89].
Ethanolic extracts of Amaranthus spinosus inhibit gastrointestinal propulsive movements in mice via the α2-adrenergic receptor pathway. A. spinosus has antidiarrheal activity due to its inhibitory effect on the propulsion and secretion of fluids through the mechanism of α2-adrenoceptors and its antiulcerogenic activity against acute gastric ulcers, by which it reduces the peroxidation of lipids generated by alterations caused by ulcers. These effects are attributed in part to the presence of phenolics, tannins and flavonoids in A. spinosus and their ability to eliminate free radicals [90].
Anoda cristata, Cnidoscolus aconitifolius and Crotalaria pumila have counteract effects on Helicobacter pylori [91], a gram-negative bacterium responsible for triggering chronic gastritis, peptic ulcer diseases and gastric cancer [92]. Dichloromethane extracts of these three species exert an inhibitory effect on bacterial growth, with minimum inhibitory concentrations (MICs) of 62.5, 125 and 250 µg/mL, respectively, and inhibit approximately 50% of the adhesion of the bacterium to human adenocarcinoma gastric cells (AGS). The inhibitory activity against H. pylori is related to acacetin and diosmetin. Consequently, the extracts have potential for use in prophylactic treatments to eradicate H. pylori [91].
In addition to the direct consumption of quelites, the ability of fermentation processes to improve the functional activity of bioactive compounds has also been evaluated; for example, the effects of lactic acid fermentation of the juice of Portulaca oleracea with Lactobacillus kunkeei B7 have been examined [93,94]. In this case, fermentation improved both the juice's antioxidant capacity and the bioavailability of vitamin B 2 and increased the levels of phenolic compounds, γ-amino butyric acid and α-linalool. The results showed that the fermented juice of P. oleracea decreases the production of intracellular ROS, preserves the integrity of monolayers of Caco-2 cells with inflammatory stimuli and limits the production of proinflammatory mediators such as prostaglandin E2 via cyclooxygenase enzymes and nitric oxide via iNOS, IL-8 and MCP-1. As with dietary fiber, the fermented juice of P. oleracea has the ability to preserve the integrity of the intestinal barrier, thus counteracting intestinal inflammation and oxidative damage [95].

Other Disorders
The ethanolic extracts of C. ambrosioides have an anti-arthritic effect according to the results of an experiment with mice with arthritis induced by type II collagen antibody applied at a dose of 5 mg/kg. The results indicate that these extracts reduce the percentage of neutrophils and macrophages and the number of bone marrow cells and increase the number of lymphocytes and cells in inguinal lymph nodes. This treatment reduces the serum concentration of proinflammatory cytokines (IL-6 and TNF-α), which cause the destruction of joints; consequently, the extract of C. ambrosioides protects joints by delaying bone density loss and cartilage and bone deformities [95]. C. ambrosioides has also been studied as an antifertility or contraceptive agent. Ain et al. [96] found that methanolic leaf extracts exert antifertility effects in adult male Sprague-Dawley rats with partial sterility induced by altering the spermatogenic cycle via oxidative stress and hormone imbalance. Although additional studies are needed, these findings imply the possible use of these extracts in reproductive mechanisms, without adverse phytotoxic effects. Additionally, aqueous extracts of C. ambrosioides have hypotensive properties and are partially associated with cardiac effects [97], and the methanolic extracts of C. ambrosioides induce an endothelium-dependent vasodilator effect by stimulating muscarinic receptors, which are involved in the opening of potassium (K + Ca) channels; these effects are attributed to kaempferol, quercetin and associated compounds [98].
Studies of neurodegenerative disorders indicate that P. oleracea extracts have anti-apoptotic and antioxidant effects in rats with brain damage induced by rotenone, a neurotoxin. Moneim et al. [99] assessed the extracts of P. oleracea (1.5 mL/kg) administered to Wistar albino rats with induced brain injury with rotenone (12 mg/kg) and Parkinson-like degeneration, and they found a significant decrease in apoptotic cells in the striatum. The results are explained by immunohistochemical detection, which indicated that P. oleracea treatment increased the expression of B-cell lymphoma-2 (Bcl-2) and decreased the levels of nuclear factor kappa B (NF-κB) as a consequence of high synthesis of ROS and a reduction in thiobarbituric acid reactive substances, nitrite/nitrate and lactate dehydrogenase. Nevertheless, cultivated and wild forms of P. oleracea should be assessed in more detail, because this species has other compounds not considered in the approach, such as α-tocopherols and omega-3 acids (e.g., alpha-linoleic acid), among others [72].
The leaves and young stems of quelites have functional compounds such as phenolic acids, flavonoids (isoquercitrin, nicotiflorin, rutin, 4-hydroxybenzoic acid, syringic acid, vanillic acid), ascorbic acid, betanin, amaranthine, iso-amarathine, betacyanins and other compounds recorded previously, whose current initiatives are evaluated by extracts or infusions of quelites, assumed to be a complex of compounds, to assess their beneficial effect in preventing metabolic syndrome [83,84], cancer, rheumatoid arthritis [95], chronic inflammatory disease, systemic joint disorders leading to joint damage and structural bone damage [100,101]. Furthermore, they have prophylactic potential against brain damage and neurodegenerative diseases related to oxidative and gastrointestinal stress [90,99].

Antibacterial and Antifungal Activity of Quelite Extracts
In relation to the antifungal effects of edible leafy plants, it was experimentally demonstrated that the extracts, leaves and stems of Amaranthus retroflexus have antifungal effects on five fungal strains: Penicillium verrucosum var. verrucosum (NBIMCC 2003 NRRL F-143), P. expansum, Fusarium graminearum (NBIMCC 2294 IMI 155426), Aspergillus ochraceus (NBIMCC 2002 IM-BAS) and A. niger [102]; all of these fungi produce different mycotoxins that affect human health. Galinsoga parviflora Cav. has antibacterial and antifungal effects against Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Aspergillus niger and Candida albicans [103], and the compounds identified as probable inhibitors include caffeoyl derivatives, isoquercitrin, quercimeritrin and quercetagetin [104]. Portulaca oleracea has antibacterial, antifungal and antiviral activities against gram-negative strains such as Escherichia coli, Pseudomonas aeruginosa and Neisseria gonorrhoeae, and gram-positive strains such as Staphylococcus aureus, Bacillus subtilis and Streptococcus faecalis, as well as antifungal activity against Candida albicans [105]; additionally, P. oleracea has protective effects against dermatophytes of the genus Trichophyton [106] and displays antiherpes properties against simplex virus type 2 [107].
Begonia maculata, B. soli-mutata, B. goegoensis, B. foliosa, hybrid Begonia x erythrophylla, B. thiemei, B. peltata, B. heracleifolia, B. dregei and B. mexicana have antibacterial effects against Escherichia coli (ATCC 25922), Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa and Citrobacter freundii; Escherichia coli is specifically inhibited by extracts of Begonia maculata leaves, and Citrobacter freundii is inhibited by extracts of Begonia thiemei and B. foliosa [116,117]. The different effects are an indicator of the different chemical compositions of the extracts or the different reactions of the pathogenic bacteria.
Edible plants have potential use in agriculture and livestock. Phytolacca dodecandra has natural fungicidal activity against chocolate spot caused by Botrytis fabae, a leaf disease of fava bean (Vicia faba L.) [119], and it has a bioinsecticidal effect against the larvae of ticks (Rhipicephalus appendiculatus), organisms that transmit diseases to cattle and cause severe losses of livestock [120]. P. dodecandra has antibacterial activity against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 8739 and Pseudomonas aeruginosa ATCC 9027 [121]. P. dodecandra contains various secondary metabolites, such as polyphenols, flavonoids, tannins, saponins, alkaloids, leucoanthocyanins, anthocyanins, steroids and triterpenoids, compounds to which antifungal and antibacterial properties are attributed [120,121]. Phytolacca americana has potential effects on periodontal inflammatory diseases and on caries caused by Porphyromonas gingivalis and Streptococcus mutans and has potential effects against Escherichia coli, and its effects are attributed to high concentrations of kaempferol, quercetin, quercetin 3-glucoside, isoquercitrin and ferulic acid [122]. Phytolacca tetramera has antifungal effects against Colletotrichum gloeosporioides (Penz.) Sacc., a fungus that causes losses in the production of agricultural, forestry and ornamental crop species [123].

Remarks and Perspectives
The efforts and natural and economic resources of the global production and marketing of food have focused on a few species or products, which has led to an increase in diet homogenization, with nutritional consequences and repercussions on health, generating another source of malnutrition in addition to that caused by dietary changes or transformations. Consumption patterns indicate that there is reduced consumption of vegetables [5] and that a small number of leafy plant species, which can provide high levels of nutrients, are marketed. In contrast, among indigenous communities, a large number of plant species with edible stems, leaves, vines and flowers are consumed and locally marketed. In Mexico, these plants are known as quelites or quilitl in the Nahuatl language, although this group of plants also takes other names in indigenous native languages and comprises more than 250 species. However, in Mexico, no more than 10 domesticated species occupy most of the cultivated area, corresponding to 12.6 million hectares (FAOSTAT, 2019) [1]. The inclusion of quelites in people's diet depends on documented knowledge of their nutritional and nutraceutical potential. The most studied genera with species native to Mexico are Amaranthus, Chenopodium, Begonia, Crotalaria, Anoda, Cyclanthera, Calandrinia, Porophyllum, Taraxacum, Tinantia, Xanthosoma, Lippia, Piper, Peperomia, Cucurbita and Galinsoga. Quelites provide proteins, amino acids, minerals, vitamins A, B complex, C and E and a significant amount of bioactive compounds, such as carotenoids, betalains, flavonoids, phenolic compounds and, in some cases, alkaloids and condensed tannins, among other nutrients.
In terms of nutrients, quelite species provide 2.7% to 44.2% protein based on dry weight (50 g, dietary reference intake (DRI)) and all essential amino acids except tryptophan in quantities that vary from 1.76 to 6.7 g/100 g protein (DRI, 23-33 mg/g protein), including histidine, which is indispensable for children and pregnant women. Quelites also provide micro-and macroelements; for example, 100 g of raw Amaranthus spp. provides 13.6 and 3.8 mg of Fe and Zn, respectively, a sufficient amount of Fe (DRI of 10 mg/day) and 25.3% of the total required Zn (15 mg/day, DRI); both of these elements are deficient in people of poor families with low income. Additionally, quelites contain K, Ca, Mg, P, S, Mn, Na, B, Mo, Cu and Co as well as substantial amounts of vitamins A, B 1 , B 2 , B 3 , B 6 , E, and C, plus niacin.
In this review, many experimental assays provided evidence of the potential effects of quelite extracts to prevent, manage and probably control current human health problems, encouraging various theories and explanations of the effects. In this sense, the extracts of Anoda cristata, Portulaca oleracea and Cnidoscolus chayamansa present hypoglycemic activity to prevent diabetes. In addition, Chenopodium ambrosioides, Cnidoscolus aconitifolius, Portulaca oleracea and Amaranthus cruentus extracts have antitumor activity and improve the immune system. Polygonum aviculare extracts caused a decrease in lipid peroxidation, and Amaranthus spinosus extracts have antidiarrheal activity; both of these extracts have been proposed to prevent obesity. Anoda cristata, Cnidoscolus aconitifolius and Crotalaria pumila extracts displayed experimental anti-Helicobacter pylori effects.
In the antibacterial and antifungal assays and based on an MIC < 100 µg/mL, the extracts with good antimicrobial activity were those of Suaeda nigra, Eryngium foetidum, Cestrum nocturnum and Solanum torvum against Staphylococcus, Enterococcus, Bacillus, Escherichia, Pseudomonas, Salmonella and Candida strains. In addition, Porophyllum ruderale and Persea americana extracts inhibited the growth of Leishmania amazonensis and Streptococcus strains, respectively (Table 5).
Lastly, there were a few documented cases on the use of fermented plants, plant parts or plant juices of quelite species. For example, Filannino et al. [91] and Di cagno et al. [92] found that lactic acid fermentation of the juice of Portulaca oleracea improved the bioavailability of bioactive compounds and enhanced functional activity. This finding opens other possibilities of the use of other vegetable species to concoct beverages.