1.1. Methodology and Strategies

The elaboration of this review was based on the following stages: identification of the theme and development of the guiding question; establishment of inclusion and exclusion criteria, analysis, and selection of articles; interpretation of data and results; and the writing of this paper. The guiding question was “What are the biological properties of genus Syagrus palm trees?” The inclusion criteria adopted were studies related to the proposed theme published in either Portuguese or English between 2005 and 2021, indexed on online databases, such as U.S. National Library of Medicine (PubMed), ScienceDirect, Scopus, and Scientific Electronic Library Online (SciELO). Both reviews and original articles were included. In turn, repeated studies, studies that do not address the proposed theme, incomplete studies, duplicates, and monographs were excluded.

After the literary search, 80 articles were selected using the inclusion and exclusion criteria. The analysis of the selected studies made it possible to identify variables, observations, and data that gathered the knowledge about the potential of Syagrus palm trees. Both the analysis and the relationship of the data extracted from these articles were developed descriptively, making it possible to count, observe, describe, classify, and organize the knowledge generated about Syagrus palm trees’ properties.

2.1. Antibacterial Activity

Bacterial infections are a major public health problem worldwide, especially due to the high levels of resistance to antimicrobials, consequently resulting in failure treatments, hospital readmissions or prolonged hospitalizations, high rates of morbidity and mortality, and high costs to health systems. With the phenomenon of bacterial resistance associated with little discovery of drugs, the search for new therapeutic options of low cost and greater efficacy has found space and strength in the study of natural products against sensitive and resistant bacterial strains, especially against Staphylococcus aureus [27–29].

Silveira et al. [30] studied the antibacterial activity of the fruit and almond extracts of Syagrus oleracea, popularly known as guariroba, and tested against Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853, and Escherichia coli ATCC 25922, inhibiting bacterial growth up to 74% (Table 1). Hughes [23] analyzed the antimicrobial potential of Syagrus coronata, popularly known as ouricuri or licuri, evaluating its potential against Bacillus cereus CCMB 282, S. aureus CCMB 285, S. aureus CCMB 262 (resistant to streptomycin and dihydrostreptomycin), and S. aureus CCMB 263 (resistant to novobiocin) (Table 1). The extracts showed antibacterial activity with minimum inhibitory concentrations ranging from 190 to 3120 μg/mL. This activity was probably related to the complex that phenolic compounds in the extracts formed with extracellular proteins of the bacterial membrane.

Bessa et al. [27] evaluated the activity of essential oil and commercial oil of S. coronata against the strain of S. aureus UFPEDA 02 and clinical isolates of methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) (Table 1). Bacteriostatic and bactericidal effects were observed when both oils were tested in all of the samples, although a higher concentration of the commercial oil was required.

In the study conducted by Santos et al. [31], anti-S. aureus activity was also evaluated from the essential oil of S. coronata seeds, and similar results were observed for both S. aureus UFPEDA 02 strain, and multidrug-resistant S. aureus clinical isolates (Table 1). In this same study, an in vivo experiment with Galleria mellonema was performed, and it was observed that the treatment with essential oil of S. coronata in infected larvae increased the survival rate of the larvae by 60%. In addition, a reduction of 4 log CFU/mL in bacterial load was observed after 3 days of treatment. Therefore, evidencing the antibacterial potential of natural products extracted from plants of this genus, highlighting the anti-S. aureus activity from the essential oil of S. coronata, which is rich in compounds with this property, such as lauric, oleic, and linoleic acids [27].

The mechanism of action of both S. coronata and S. oleracea is not fully elucidated, but lauric acid, one of the main compounds in those plants, acts on the destruction of the cell membrane and interferes with cellular processes, such as signal transduction and transcription [32, 33]. Capric acid, also one of the main compounds in those plants, can damage the bacterial membrane due to its hydrophobicity, thereby facilitating the entrance of hydrogen ions from the extracellular environment and the complete inactivation of the bacterial cells [33, 34].

Besides that, S. coronata oil was proved to be safe when evaluated by biochemical, hematological, and histological parameters and did not demonstrate mutagenic nor genotoxic effects even in high doses [35].

2.2. Antibiofilm Activity

Biofilms are complexes composed of a set of bacteria encapsulated in an array of extracellular polymeric substances linked to biotic or abiotic surfaces. This system offers greater security, stability, oxygen, and nutrients to the microorganisms of this complex, thus protecting them from stress and increasing their survival potential [36]. This virulence factor is the main agent responsible for chronic infections because this persistence conferred by the biofilm results in treatment failure, making it necessary to apply new therapeutic approaches [37].

In the study of Santos [31], with the essential oil of S. coronata rich in dodecanoic acid, it was evaluated the activity of this oil against the biofilm of S. aureus UFPEDA 02. As a result, a significant reduction in the matrix was observed of biofilm only at concentrations of 312 and 624 μg/mL; however, the viability of biofilm cells was significantly reduced at all concentrations tested, showing a reduction greater than 50% in the concentration of 156 μg/mL and a reduction of almost 100% at concentrations of 624 and 1248 μg/mL. In addition, changes in the cellular structure of S. aureus were also observed, as well as a loss of roughness in the multiple layers of the three-dimensional structure of the bacterial biofilm.

Another similar research performed by Junior [38] evaluated the antibiofilm activity of the essential oil of S. coronata, rich in dodecanoic, decanoic, and octanoic acids, against the Proteus mirabilis UFPEDA 737 isolate. Above 500 μg/mL, the essential oil inhibited biofilm formation by more than 55%. The mechanism of action of S. coronata is not fully elucidated, but its main compounds lauric acid, capric acid, and caprylic acid affect cell membranes and bacterial adhesins, virulence genes, capsule production, and cell adhesion, respectively [39].

2.3. Antiparasitic Activity

Even in modern society, parasitic infections are still one of the world′s public health problems, causing millions of deaths each year. Parasitic infections are considered as neglected tropical diseases, mainly because they mostly affect people in underdeveloped countries, where a large part of the population lives in a situation of social vulnerability. Many of these diseases have high cytotoxicity treatment so new therapeutic alternatives are needed to fight these infections [40, 41].

Leishmaniasis is an endemic parasitic infection caused by more than 20 species of Leishmania. Present in 97 countries, leishmaniasis affects more than 1.3 million people every year. This infection has three main forms: cutaneous leishmaniasis, visceral leishmaniasis, and mucocutaneous leishmaniasis [42]. The treatment of leishmaniasis is very problematic, due to the increase in parasitic resistance to currently used therapies, serious side effects, unsatisfactory results, and high cost of treatment [43].

Rodrigues et al. [24] analyzed the anti-Leishmania amazonensis activity of the aqueous polymeric extract of S. coronata rich in procyanidin. They tested the potential of this extract against the promastigote and amastigote forms of L. amazonensis. The extract of S. coronata, at a concentration of 50 μg/mL, was able to inhibit the growth of promastigotes after 30 minutes and make 100% of the promastigotes unviable after 60 minutes. In addition, increased cell volume and membrane rupture were observed in the promastigotes treated with aqueous extract, suggesting that the extract of S. coronata induced osmotic dysregulation in L. amazonensis promastigotes (Figure 1). In the same study, the extract of S. coronata was also able to reduce the index of association between macrophages and amastigotes of L. amazonensis, with a concomitant increase in the production of nitric oxide (NO). When mouse peritoneal macrophages were pretreated with the extract at a concentration of 33 μg/mL, the association index was reduced by 70.4%, and NO production increased by 158.3% when compared to the control. When the treatment was applied 24 hours after macrophage infection, the 33 μg/mL of the crude aqueous extract was able to reduce the association index by 71% and increase NO production by 90.4%. Therefore, demonstrating the potential of using this plant as a leishmanicidal drug, mainly due to the increase in NO production, which potentiates the mechanisms of death of L. amazonensis.

Chagas disease or American trypanosomiasis is an anthropozoonosis caused by Trypanosoma cruzi. This infection is also considered a neglected tropical disease and is an important social and public health problem in Latin America. The number of people infected with T. cruzi in the world is substantial, being between 6 and 7 million people infected. The treatment of Chagas disease is effective in patients in the acute phase of the disease; however, when the person has been infected for a long period, the effectiveness of the medication decreases, and the treatment becomes ineffective. In addition, the drug can cause side and adverse effects due to its high cytotoxicity to mammalian cells [44, 45].

Souza et al. [46] evaluated the trypanocidal activity of the essential oil of S. coronata seeds. Their results showed that half of the maximal inhibitory concentration (IC₅₀) for T. cruzi epimastigotes was 100.6 ± 38 μg/mL, the IC₅₀ for amastigotes was 408.33 ± 23.36 μg/mL and the lethal concentration (LC₅₀) for trypomastigotes was 182.49 ± 58.05 μg/mL. Thus, it was demonstrated that the essential oil of S. coronata was able to inhibit the growth of epimastigotes and decrease the viability of trypomastigotes with moderately toxic concentrations.

2.4. Antioxidant Activity

In metabolisms, there are several oxidative processes necessary for cell survival. These processes result in the production of free radicals, which are involved in a series of regulatory processes, such as cell proliferation, apoptosis, and gene expression. However, in excess, these free radicals cause changes in protein structure, amino acid oxidation, DNA damaging, aging, and other harms. Therefore, in recent years there has been an increase in the demand for molecules and products that protect the individual against oxidative stress, and plants have been shown to be strong candidates due to their chemical compositions [47, 48].

Andrade et al. [49] studied the antioxidant activity of Syagrus romanzoffiana, popularly known as Jerivá. This property of the plant was evaluated using the β-carotene/linoleic acid method, which assesses the activity of inhibiting free radicals formed in lipid peroxidation, and ABTS and DPPH methods, which are related to the search for free radicals. Using 0.4 mL of extracts from the pulp and kernel cake of S. romanzoffiana, inhibition rates of oxidation were 97.00 ± 0.43% and 95.13 ± 0.7%, respectively, when the β-carotene method was applied. The ABTS method also demonstrated high antioxidant activity in the samples, all of which were greater than 100 μM Trolox·g⁻¹. Using 30 μL of the pulp extract, a result of 2498.49 ± 186.7 μM Trolox·g⁻¹ was obtained. In the same concentration of the kernel cake extract, the result was lower, obtaining 1314.87 ± 29.78 μM Trolox·g⁻¹. In the DPPH method, the concentration necessary to reduce the amount of DPPH (EC₅₀) was measured. The best result once again was from the pulp extract of S. romanzoffiana, presenting an EC₅₀ = 96.97 ± 3.74 g fruit·g⁻¹ DPPH, whereas the kernel cake extract showed EC₅₀ of 331.80 ± 3.95 g fruit·g⁻¹ DPPH. The authors state that the large number of phenolic compounds in this oil may have contributed to this antioxidant activity [49].

According to Coimbra and Jorge [50], the antioxidant activity of Jerivá pulp oil can be justified by a large amount of β-carotene and tocopherols, with a total of 1219.01 ± 16.21 μg/g for carotenoids and a total of 323.50 ± 7.85 mg/kg for tocopherols, with α-tocopherol being the most abundant (273.53 ± 4.79 mg/kg). Both compounds have proven antioxidant activity in vivo and in vitro. β-Carotene can function as a lipid scavenger and an oxygen extinguisher because of its unique structure of conjugated double bonds and ionone rings [51], and tocopherols can deactivate reactive oxygen species, inhibit protein oxidation, and prevent the propagation of lipid peroxidation by scavenging lipid peroxyl radicals [52], thus showing their potent antioxidant activity.

Belviso et al. [25] evaluated the antioxidant activity of S. coronata using the methods of DPPH and ABTS. The extract of toasted S. coronata seeds showed better antioxidant activity, presenting DPPH = 7.01 ± 0.23 μM TE/g and ABTS = 5.31 ± 0.74 μM TE/g, whereas the extract of raw seeds showed DPPH = 5.88 ± 0.16 μM TE/ge ABTS = 4.07 ± 0.17 μM TE/g.

The antioxidant activity of S. oleracea was also tested in the studies by Silva et al. [53] and Siqueira et al. [54]; however, the results were not as promising as those found in the two plants shown above. In the study by Silva [53], the EC₅₀ of S. oleracea extract in the DPPH test was 425.5 ± 1.9 μg/mL, this result demonstrates low antioxidant activity. Siqueira et al.’s [54] obtained rate inhibition of oxidation by the ß-carotene method was 0.7 ± 0.1%/g, a very low rate.

2.5. Prebiotic Activity

Approximately 100 trillion microorganisms are inhabiting the human gastrointestinal tract. This microbiota present in the gastrointestinal system is part of a complex ecosystem that plays an important role in maintaining people′s well-being and health [55]. Prebiotics are compounds selectively used by host microorganisms that can promote health benefits to the individual. They can be used as an energy source and stimulate the growth of microorganisms in the intestinal microbiota. Despite the benefits, the prebiotics available are not easily accessible, due to the high cost, so new alternatives are sought, such as the use of medicinal plants [49, 56].

Andrade et al. [49] studied the prebiotic potential of S. romanzoffiana pulp and kernel cake through the analysis of factors such as microbial growth, fermentation, and organic acids produced by the strains Bifidobacterium lactis BLC1, Lactobacillus casei BGP93, and Lactobacillus acidophilus LA3, in addition to of the pH change. The S. romanzoffiana pulp showed the best results, showing significant growth of 9.09 ± 0.09 log CFU/mL, 9.20 ± 0.11 log CFU/mL, and 8.76 ± 0.12 log CFU/mL for B. lactis, L. casei, and L. acidophilus, respectively. The greater growth of the probiotic strains was the result of the use of the carbon present in the S. romanzoffiana pulp as an energy source for bacteria. A greater decrease in pH was also observed after the administration of the S. romanzoffiana pulp, proving once again the probiotic potential of the plant, since a reduction in pH can be caused by the production of organic acids such as lactic, acetic acid, propionic, and butyric by bacteria during fermentation, thus indicating bacterial growth of probiotic strains and possible inhibition of the proliferation of pathogenic bacteria.

2.6. Antiulcerogenic Activity

Peptic ulcers are an increasingly common problem in the world population, affecting millions of people every year. They are lesions in the gastroduodenal mucosa, which cause frequent pain and gastrointestinal hemorrhage, resulting in loss of the patient’s quality of life [57].

Silva and Parente [58] studied the antiulcerogenic activity of a galactomannoglucan extracted from the pulp of S. oleracea. In this in vivo experiment, male Swiss mice exposed to absolute ethanol, a substance that attacks the mucous membrane of the stomach, presented widespread and intense gastric hyperemia, in addition to thick lesions (control group). On the other hand, the group treated with galactomannoglucan extracted from S. oleracea before the exposition to absolute ethanol, had a stomach close to normal, with a great reduction in gastric hyperemia and formation of lesions after the administration of ethanol, thus evidencing the antiulcerogenic and gastroprotective activity of this natural compound (Figure 2). This gastroprotective activity was attributed to the chemical structure of galactomannoglucan, which is characterized by an initial chain of ß-D-galactose linked to (1–3) and terminal residues composed of α-D-glucose linked to (1–4) and is similar to antiulcerogenic polysaccharides that can induce mucus production.

2.7. Anticholinesterase Activity

Alzheimer’s is a neurodegenerative disease that progressively deteriorates mental functions. In this disease, the cholinergic function is affected, like acetylcholine, a neurotransmitter responsible for conducting electrical impulses from one nerve cell to another, is reduced in quantity due to the rapid hydrolysis carried out by acetylcholinesterase. Therefore, cholinesterase inhibitors can be used in the treatment of this disease because they would inhibit the premature hydrolysis caused by acetylcholinesterase [59, 60].

El-Hawary et al. [61] evaluated the anticholinesterase activity of hydroalcoholic extracts of leaves and fruits of S. romanzoffiana in an in vivo experiment (Figure 3). The experiment was based on the administration of doses of 50 and 100 mg/kg.b.wt. of S. romanzoffiana extracts in rats for 2 months. Treatment with 50 mg/kg.b.wt. of the fruit extract resulted in a 21.5% reduction in acetylcholinesterase activity, whereas treatment with 100 mg/kg.b.wt. of this same extract resulted in a reduction of 26.5%. Treatment with 50 mg/kg.b.wt. of the extract of the leaves of the jerivá, resulted in a reduction of 22% in the activity of acetylcholinesterase, already the treatment with 100 mg/kg.b.wt. of this same extract resulted in a reduction of 29%. Both extracts showed significant reductions in cholinesterase activity, mainly due to the richness of fatty acids, flavonoids, and stilbenoids present in the extracts.

2.8. Hypoglycemic Activity

Diabetes mellitus is a metabolic disease characterized by an increase in blood glucose. It is a disorder that affects more than 400 million people worldwide and presents many health risks, which can cause microvascular and macrovascular complications, kidney failure, myocardial infarction, stroke, and the need to amputate limbs, thus reducing the quality and life expectancy of individuals. One of the alternatives for treating diabetes mellitus is to delay glucose absorption by inhibiting carbohydrate hydrolysis enzymes, such as α-glucosidase, and this inhibitory potential has been discovered in natural products [62, 63].

Lam et al. [26] evaluated the potential of S. romanzoffiana seed extract to inhibit α-glucosidase. As a result, it was observed that 10 μg/mL of the ethanolic extract of S. romanzoffiana inhibited α-glucosidase by 55% and the butanoic fraction of this extract at the same concentration was able to inhibit even more (73%) (Figure 4). In addition, 8 compounds were identified in the extract and subsequently had their inhibitory activities evaluated, where 2 of them had excellent anti-α-glucosidase potential. The first isolated compound was the stilbene-phenylpropanoid 13-hydroxycompasinol A. This compound showed an inhibitory effect with an IC₅₀ of 6.5 μM, and the second compound was the dimeric stilbenoid scirpusin C, which showed an even greater inhibitory effect, with an IC₅₀ of 4.9 μM.

In the study of Lam and Lee [64], 6 other compounds extracted from S. romanzoffiana had their hypoglycemic activity evaluated, and 4 of them showed anti-α-glucosidase activity. Syagrusins A and B had ICs₅₀ of 16.9 and 23.7 μM, respectively, 5-hydroxyapanol had IC₅₀ of 12.8 μM, and the first phenylpropanoid had IC₅₀ of 10.7 μM, thus, once again showing the potential that S. romanzoffiana extract and compounds have for the development of hypoglycemic drugs, especially stilbenoids.

2.9. Pharmacological Properties Suggested by Ethnobiological and Ethnopharmacological Studies

Ethnobiological and ethnopharmacological studies are greatly important for the discovery of new drugs of plant origin. These studies are based on research on the experiences of a community with the use of medicinal plants and their applications. From this, the most promising plants and genera are delimited, making the use of these plants more reliable and safer [65, 66].

Some researchers have already indicated the popular use of products of the Syagrus genus. In the study performed by Ribeiro et al. [67] in the northern microregion of Araguaia, in the state of Mato Grosso, the fruit of the Syagrus comosa (Mart.) plant, popularly known as bacuri, is used for conjunctivitis and S. oleracea for indigestion, diarrhea, and as an appetite stimulant. In the study performed by Rufino et al. [68] in a community near the Catimbau Valley National Park, municipality of Buíque, Pernambuco, was reported that S. coronata is used for the treatment of eye inflammation, mycoses, wound healing, and pain in the spine.

Junior, Ladio, and Albuquerque [69], in the community of Carão, municipality of Altinho, in the harsh region of Pernambuco, indicated that the plant Syagrus cearensis, popularly known as coco-catolé, had anti-inflammatory activity. Individuals in that community reported improvement after using S. cearensis for pain caused by cuts, swelling of wounds, redness, and itchy eyes. However, despite the use of these plants in these communities, experimental studies must be conducted to prove their effectiveness and better elucidate the mechanisms of action of these natural products.

2.10. Other Applications

In addition to the pharmacological properties already mentioned in this article, plants of the Syagrus genus still have other possible applications (Table 2) [13, 14, 70–80], mainly due to their chemical composition. The areas that stand out the most are biotechnology, for biodiesel production at an equal quality or better than the biodiesels on the market. Another success is in bioremediation, bringing fast, cheap, and efficient absorption of effluent materials.