Plant ingredients in Thai food: a well-rounded diet for natural bioactive associated with medicinal properties

Introduction

Since the pandemic of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) began in 2019, searching for new potential antiviral agents and prophylactics has driven priorities in public health research and the scientific community. Furthermore, treatment failure, drug side effects, and resistance have broadly inspired a shift in direction to investigating natural plant products as sources of effective bioactive agents. This updates a previous compilation of 207 plant species reported as having antiviral activity against essential and clinically significant viruses such as human immunodeficiency virus (HIV), herpes simplex virus (HSV), influenza, and hepatitis C (Mohan et al., 2020b).

Edible plants have the advantages of featuring milder toxicity profiles and being easy to access. In Indian cuisine, 38 edible plant species used as food or nutraceuticals have shown anti-retroviral activity, some of which also possess anti-inflammatory, immunomodulatory, or angiotensin-converting-enzyme (ACE) inhibitory activity (Patel et al., 2021). Herbal medicine is also a potent source of compounds with therapeutic properties. Antioxidant and antiviral potential has also been demonstrated in a summary of 18 herbal antimicrobial agents including clove, portulaca, tribulus, eryngium, cinnamon, turmeric, ginger, thyme, pennyroyal, mint, fennel, chamomile, burdock, eucalyptus, primrose, lemon balm, mallow, and garlic (Parham et al., 2020). Some similar articles have also been published on selected plant species. For instance, Allium cepa (Amaryllidaceae) juice, methanolic extract, and constituents like allicin, quercetin, and allyl methyl disulfide have shown anti-inflammatory effects in different models and with different mechanisms of action (Marefati et al., 2021). A review article of different plant parts, extraction solvents, and seed oil of Coriandrum sativum (Apiaceae) experimentally demonstrated anti-inflammatory effects in macrophages, mice, and rats (Sari, Bellatasie & Ifora, 2021). A trypsin inhibitor protein from seed of Tamarindus indica (Fabaceae) is proposed to have utility for inhibiting proteases related to SAR-CoV-2 infection in the worsened inflammatory condition in obesity (de Morais et al., 2021). Curcumin from Curcuma longa (Zingiberaceae) is also proposed as a potential prophylactic therapeutic for COVID-19 due to its observed antiviral activity against ten types of enveloped viruses that cause human diseases combined with an immunomodulatory effect (Thimmulappa et al., 2021). Additionally, xanthones in many plant species, including Garcinia cowa (Clusiaceae), can potentially treat inflammatory skin diseases through different mechanisms (Gunter et al., 2020).

Alongside an active lifestyle, a healthy and functional diet is of interest for maintaining and promoting well-being to prevent, delay, and even treat ailments. That is, functional food may help to boost the immune system, reduce risk of noncommunicable diseases, and improve memory or physical condition (Topolska, Florkiewicz & Filipiak-Florkiewicz, 2021). Several edible and medicinal plants serve as daily elements of the diet in traditional Thai cuisine, which emphasizes aromatic components, flavor, and appearance and utilizes a range of preparation methods such as spicy salads, steaming or boiling, stir-frying, frying, and chili pastes for a dip. Moreover, Thai cuisine includes many coconut-milk-based curry pastes with slightly different compositions like red curry, sweet green curry, yellow curry, nutty curry, a fusion of Thai and Indian styles (Massaman curry), and non-coconut-milk based curry pastes such as the famous Tom Yam (hot and sour soup with or without coconut milk), Tom Kah (coconut milk with galangal rhizome and kaffir lime leaves), and Gaeng Som (sour fish curry paste soup) (Kanchanakunjara, Chantachon & Koseyayotin, 2017; Khanthapok & Sukrong, 2019). The unique combination of vegetables, herbs, and spices used in Thai dishes makes Thai food an excellent example of a healthy diet. Notably, many of these plants have also been used in traditional medicine over generations to maintain health or relieve and cure ailments and infectious diseases. With the increasing problems posed by antimicrobial resistance, viral diseases, and inflammatory conditions related to various symptoms and diseases, the ingredients and medicinal plants in Thai dishes could comprise a valuable potential resource for the discovery of bioactive compounds with anti-infective and protective effects.

Here, we highlight different plant species and parts used in Thai food and traditional medicine simultaneously, as part of a functional diet and as phytomedicine; we also discuss their important metabolites, therapeutic uses, and biological and pharmacological activities. Furthermore, this review summarizes an update of recent research papers on plant extracts and, in some instances, isolated compounds that have demonstrated anti-inflammatory effects and antibacterial activity against selected critical antibiotic-resistant bacteria (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) or antiviral activity against clinically significant human viruses such as influenza virus, herpes simplex virus, Zika virus, and SARS-CoV-2.

The present review provides an easy-to-access list of edible and medicinal plants as a database, which is vital in developing further applications in clinical practice and drug discovery to comply with the UN goal of sustainable development to promote good health and well-being. Moreover, these plants might be integrated into food processing and manufacturing or added into any diet regimen as ingredients that promote and restore health. Our review can guide further research and offers highly interesting material for other scientists working on several aspects of plant-related life sciences, natural products, and the international plant science community. Thai food is complex, and its plant ingredients are abundant in tropical and subtropical regions; that is, the plants discussed here are not specific to the South-East Asia region. To the best of our knowledge, our work represents one of the most comprehensive indexes of diverse plants from a single cuisine that feature bioactivities that impact human health. It can inform and increase public awareness about the importance of ongoing research activities in plant science, phytochemistry, and pharmacognosy.

Survey methodology

For the development of this review, globally-recognized names of the plant materials selected based on their use in Thai food and folk medicine were obtained from Plants of the World Online (POWO; https://powo.science.kew.org/) and the International Plant Names Index (IPNI; https://www.ipni.org/). Related literature dated from 2017 to 2021 was then sourced from scientific databases including PUBMED, Science Direct, and Google Scholar by searching with the term “Plant name” followed by the keyword “Anti-inflammatory” or “Antibacterial” or “Antiviral.” After carefully considering the obtained literature, we took only those publications that fit our scope of review. We proceeded to develop our database and produce this review. The compiled plant species and associated phytochemicals presented here have demonstrated the most promising health benefits and advantages with regard to targeting lead compounds.

An overview of culinary herbs, spices, and medicinal plants in thai food

We summarized a selection of 69 species (33 families) from edible and medicinal plants used in Thai food, and also Zingiber cassumunar in the family Zingiberaceae. The selection covers plant parts consumed as vegetables or as ingredients in the preparation of many Thai dishes. Based on several phytochemical studies, all of the selected plant species are potential sources of bioactive compounds in various classes; Table 1 presents the main chemical compositions of the different plant families and genera.

Many compound classes have been screened and identified in the plant species reviewed here and found to possess various medicinal properties. For example, essential oils or volatile oils, which mainly contain terpenes and terpenoids that are known as antioxidant, antimicrobial, anti-inflammatory, antidiabetic, anticancer, and antiallergic compounds, are found in aromatic plants belonging to the families Apiaceae, Clusiaceae, Lamiaceae, Lauraceae, Myristicaceae, Myrtaceae, Rutaceae, and Zingiberaceae (Marrelli et al., 2020; Masyita et al., 2022). Likewise, the alkaloid piperine and its derivatives are found in plants of the family Piperaceae and have several documented biological activities (Tiwari, Mahadik & Gabhe, 2020). Other major classes of phenolic compounds include polyphenols, phenolic acids, flavonoids, tannins, stilbenes, lignins, lignans, and coumarins, which have shown anti-inflammatory, anti-infective, antiproliferative, and antioxidant activities (Luna-Guevara et al., 2018). Curcuminoids are another group of polyphenols found in Curcuma species of the family Zingiberaceae that have been reported as having antioxidant, anti-inflammatory, antimutagenic, antimicrobial, and anticancer properties (Hewlings & Kalman, 2017). Meanwhile, natural xanthones are an important class of compounds in Garcinia species of the family Clusiaceae that have potential for treating inflammatory skin diseases (Gunter et al., 2020). Notably, xanthones are also found in the root part of Cratoxylum formosum in the family Hyperiaceae (Table 1). Hence, non-edible parts of plants should be evaluated for their potential as additional sources of new bioactive compounds (Svobodova et al., 2017; Rodanant et al., 2017; Maduka & Ikpa, 2021). Among the 69 plant species reviewed here, the commercially used species have been thoroughly investigated for constituent bioactive substances (Jantan et al., 2019; Oyeyinka & Afolayan, 2020; Marefati et al., 2021; Sari, Bellatasie & Ifora, 2021). However, there is very little literature on some less-widely used plant species, such as Telosma cordata in the family Apocynaceae (Nguyen, 2020).

Individual plants that are also used in traditional medicine and have shown various pharmacological properties are listed in Table 2. The claimed traditional uses of the selected plants are supported by updated documentation of their pharmacological activities, including antioxidant, antimicrobial, anti-inflammatory, hypolipidemic, antihypertension, antidiabetic, and other like health benefits. In some cases, it is unclear which part of the plant is used to obtain the mentioned therapeutic effect, and there is yet insufficient comparative study of phytochemical and biological activity in different parts of a given plant species. Content of bioactive compounds might vary in different parts of the same plant and in plants of closely related genera (Buathong et al., 2019). Thus, comprehensive studies of the chemical composition and bioactive components in different plant parts and in other genera that have closed taxonomic relationships with the plants listed in this work will open more possibilities for the discovery of new sources and active compounds and hence the expansion of phytomedicine development.

An updated list of bioactivities of the selected plants

Inflammation is divided into two types: acute and chronic. Acute inflammation is a defense mechanism induced in response to harmful stimuli such as infections, injuries, and chemicals and is recognized by swelling, redness, fever, and pain. Chronic inflammation will occur if acute inflammation lingers for a long time, eventually leading to oxidative stress-mediated diseases, heart disease, diabetes, cancer, arthritis, and bowel diseases like ulcerative colitis (Marefati et al., 2021). Infectious diseases caused by microorganisms and pathogenic viruses can also induce cellular responses, activating signaling molecules such as NO and ROS that contribute to the inflammatory process by triggering the release of a cytokine storm that includes pro-inflammatory cytokines like TNF-α and interleukin (IL-1β, IL-6); this results in cell death (apoptosis) that can lead to acute respiratory distress or syndrome (ARDS), as seen after infection with SARS-CoV-2 (Donma & Donma, 2020). In this regard, we provide a recent backdated review to update the field on the discovery of many extracts and isolated compounds from plant species, with a specific focus on anti-inflammatory properties observed upon administration in study models and on antimicrobial effects demonstrated against antibiotic-resistant bacteria and clinically significant viruses.

Conclusions

Plants used as ingredients in Thai food are typically also medicinal plants with applications proven long ago in folk medicine. This review describes the great extent of available information on edible and medicinal plants and isolated molecules from Thai food sources, which until now has existed as scattered pieces of information that have never been combined. The plant list includes diverse families with therapeutic importance supported by the various pharmacological activities, significant bioactive metabolites, and updated anti-inflammatory, antibacterial, and antiviral properties for which evidence has been collected in recent years. Based on the literature, plants used as ingredients in Thai food would be justified as elements of a healthy and functional diet and as sources of up-and-coming drug candidates with lesser toxicity. Many plant species have dual activity, demonstrating both anti-inflammatory and antimicrobial effects towards antibiotic-resistant bacteria and clinically significant viruses. In addition, more than one plant species is generally used for a single dish, as in traditional medicine practice. Hence, the effect of plant-plant combinations should be evaluated so as to enhance health restoration, therapeutic effects, and the development of supplementation and pharmaceutical-related products.

In Thailand, Andrographis paniculata (Burm. f.) Wall. ex Nees or Fah Talai Jone, a plant that has been used to treat and relieve common cold symptoms for years, has been included in The National List of Essential Drugs since 1999 and has become of renewed interest because of the COVID-19 pandemic around the globe. Encapsulated powder or extract of Andrographis paniculata with its major component, andrographolide, taken as a dose of 180 mg per day for five consecutive days, was recommended by the department of medicinal services for patients with mild symptoms (Mahajaroensiri et al., 2021). Concerning toxicity, a recent research article indicated that Andrographis paniculata extract and andrographolide respectively had no toxicity and a favorable toxicity profile in six representative human cell lines from the liver, kidney, intestine, lung, and brain. Both extract and andrographolide possess anti-SARS-CoV-2 activity and should be further investigated for their bioavailability and development for clinical applications as a monotherapy or in combination with other drugs (Sa-Ngiamsuntorn et al., 2021). In addition to that exemplar, this review emphasizes a promising plant list that will be of help in encouraging further investigation into mechanisms, synergy with antibiotics, formulations, physicochemical properties, bioavailability, and clinical research for the practical utilization of bioactive plant products. Moreover, the current review shall aid in the better selection of plant parts and species and promote their evaluability as food ingredients, functional foods, beverages, dietary supplements, and herbal medicines to preserve and increase vitality, slow aging, and promote well-being.