Duckweed (Lemnaceae): A Comprehensive Reference
1. Identity: Botanical Classification, Nomenclature, and Common Forms
1.1 Botanical Classification and Genera
Lemnoideae, commonly known as duckweed, are free-floating or submerged aquatic plants from the family Araceae. The subfamily Lemnoideae includes five genera — Landoltia D. H. Les & D. J. Crawford, Lemna L., Spirodela Schleid., Wolffia Horkel ex Schleid., and Wolffiella Hegelm. — and consists of 40 taxa. Duckweed belongs to the family Araceae, subfamily Lemnoideae, with small roots (1–5 cm), shoots between one and several millimetres wide, and high biomass production, doubling its biomass in 2–4 days.
The most nutritionally and commercially studied species include:
- Wolffia globosa (Roxb.) Hartog & Plas — also known by the common names Asian watermeal and duckweed, native to Asia and found in parts of the Americas and Africa, growing in mats on the surface of calm, freshwater bodies such as ponds, lakes, and marshes.
- Wolffia arrhiza (L.) Horkel ex Wimm. — a rootless European and Asian species, used alongside W. globosa in traditional cuisines.
- Lemna minor L. — common duckweed, the most widespread temperate species and the most studied for phytochemistry and aquaculture feed value.
- Lemna gibba L. — inflated or swollen duckweed, also studied for its nutritional profile.
- Spirodela polyrhiza (L.) Schleid. — the largest duckweed genus, ancestral phylogenetically, carrying multiple roots.
- Landoltia punctata (G. Mey.) Les & D.J. Crawford — formerly classified as Spirodela punctata; morphologically intermediate between Lemna and Spirodela, representing an isolated clade distinct from both.
The genus Wolffia includes the smallest flowering plant in the world and is distinguished from other duckweeds by a combination of swollen lower parts and the lack of roots. The genus includes 11 species worldwide. The ancestral genus Spirodela has the smallest genome size (150 MB, similar to Arabidopsis thaliana), while the most derived genus, Wolffia, contains plants with the largest genome size (1,500 MB).
1.2 Commercial Strains and Tradenames
The strain known commercially as "Mankai" — Generally Recognized as Safe (GRAS) — is a cultivated strain of Wolffia globosa, an aquatic plant part of the family of plants commonly known as duckweeds. The cultivated strain was patented by the applicant as Wolffia globosa Mankai. In Southeast Asian traditional markets, W. globosa is sold under local names including khai-nam, kai-pum, and kai nhae.
1.3 Common Forms and Preparations
Duckweed is available or studied in the following forms:
- Fresh/whole plant — the traditional form consumed in Southeast Asia; fresh plants of Wolffia arrhiza and Wolffia globosa have received EU novel food approval as marketable fresh plants.
- Frozen cubes / green shake — in controlled dietary interventions, Mankai has commonly been provided as approximately 100 g frozen biomass per day blended into a "green shake."
- Dried powder — the novel food is produced by cultivation of Wolffia globosa plants under controlled conditions, washing with hot water, and drying. The novel food is a green powder obtained after drying the fresh plant material.
- Food ingredient applications — duckweed flour has been studied as a partial substitute for wheat flour in bread, cookies, pasta, and noodles.
2. Historical and Traditional Use
2.1 Southeast Asian Food Traditions
There is a long history of the use of Wolffia species, in particular Wolffia globosa, as food, especially in Southeast Asia: Burma, Laos, and northern Thailand, where it has been used as a vegetable for many generations. It has traditionally been used as a food crop in some regions of Southeast Asia, such as Laos and northern Thailand, where it is sold under the local names khai nam, kai-pum, or kai nhae (literally meaning "water-eggs"). The species is primarily harvested, rather than cultivated, twice a week from November to July.
Wolffia arrhiza has been used as a vegetable for many generations in Myanmar, Laos, and northern Thailand. It is harvested twice a week during 9 months of the year (November–July). Its Thai local name "Khai-nam" means "eggs of the water." According to Appenroth et al. (2017), the plant that was widely consumed as food in Southeast Asia was W. globosa rather than W. arrhiza. The applicant noted that W. globosa appears in recent articles among edible species sold in the market.
Known in Thai as Pham (ผำ), it is a popular item in Thai cuisine, especially in Isan. There are numerous ways of W. globosa consumption and a variety of recipes, using it either as a main ingredient (such as Wolffia crisps or "kaeng pum" — a popular vegetable dish in northeastern Thailand) or incorporating it in other foods (e.g., Wolffia-meat ball, fermented Wolffia-meat sausage, Wolffia rice noodle, Wolffia cookies, Wolffia bread, and various soups and salads).
For generations, fresh Wolffia has been eaten in Southeast Asia, often added to soups, omelets, curries, and stir-fries. Due to its rapid growth rate and the relative ease at which it grows on calm bodies of water, Wolffia globosa was traditionally only harvested, and not cultivated by indigenous peoples. The plant is now cultivated locally in rain-fed open ponds, grown commercially in Thailand, and sold in local markets throughout Thailand and Laos.
2.2 Regulatory Recognition of Historical Use
The European Union approval concerns the authorisation to market fresh plants of Wolffia arrhiza and Wolffia globosa as a new traditional food. The fresh plants can be marketed to and used by the general population. It is the European Food Safety Authority (EFSA) which has approved the use of the plants, which have a history of safe food use, in particular in Laos, Myanmar, and Thailand. These water lentils have been eaten for more than 25 years in Southeast Asia and consequently fall under the category of traditional foods, for which a fast-track Novel Food procedure was allowed and eventually approved. Both species are now listed on the Union List, which describes the conditions under which water lentils may be used, labelling requirements, and maximum contents of heavy metals and trace elements.
3. Key Constituents and Active Compounds
3.1 Proteins and Amino Acids
Duckweeds are increasingly recognized for their potential as a sustainable protein source, featuring a protein content typically ranging from 15% to 45% of dry weight and a complete amino acid profile. Reported essential amino acids include arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, valine, and tyrosine, alongside poly-unsaturated fatty acids, β-carotene, and xanthophylls.
Wolffia globosa offers all nine essential amino acids (EAAs), dietary fibers, polyphenols, iron, zinc, and vitamin B12. Mankai was found to have a high digestibility profile (89%) according to Protein Digestibility-Corrected Amino Acid Score (PDCAAS) Eurofins tests. Duckweed, including Lemna and Spirodela, is a tiny aquatic floating plant that represents a valuable source of plant protein; its protein has a well-balanced amino acid profile, giving it great potential for human food products.
The main components of dried duckweed powder were proteins (33.16%) and carbohydrates (36.73%), followed by ash 14.58%. However, nutritional composition varies substantially by species, growing conditions, and fertilizer composition. Several studies have reported the amino acid profiles of duckweed species across all five genera, demonstrating considerable variability even among species within the same genus.
3.2 Lipids and Fatty Acids
Duckweed provides 4–7% lipids, including omega-3 and omega-6. Lipid content of L. minor was higher (7.15–8.45%) in some studies, while duckweeds produced in nutrient-poor water bodies showed lower lipid content (1.8–2.5%) compared to plants grown (3–7% lipid) in water enriched with nutrients. The lipid fraction is notable for its alpha-linolenic acid (ALA, 18:3n-3) content, which is reflected in studies showing that dietary inclusion of Lemna minor increases n-3 PUFA accumulation in animals fed the plant.
3.3 Carbohydrates and Dietary Fiber
The carbohydrate content of duckweed ranges from 25–35%, serving as a reliable energy source, while its 5–15% fiber aids digestion. It contains up to 40% protein and 3% to 75% starch by dry weight, comparable to traditional protein-rich sources like soybeans and legumes. The starch fraction varies considerably across species and growth conditions.
3.4 Vitamins
Mankai (Wolffia globosa) is a fast-growing aquatic plant of the duckweed family that contains high-quality plant protein, dietary fiber, and a broad spectrum of micronutrients like iron, folate, and authentic (bioactive) vitamin B12 forms identified by LC-MS/MS (including OH-B12, Ado-B12, Me-B12, and CN-B12). In analyses comparing Mankai extracts with spirulina, no pseudo-vitamin B12 (pseudo-CN-B12) was detected in Mankai. This is significant because pseudo-cobalamin, found in many algae, cannot substitute for functional vitamin B12 in humans.
Duckweed is additionally rich in vitamins A, B-complex, and C. Bioactive compounds such as α-tocopherol (vitamin E), phytosterols, and carotenoids are richly present in duckweed.
3.5 Minerals
Iron (Fe), sodium (Na), magnesium (Mg), potassium (K), zinc (Zn), and calcium (Ca) are the predominant minerals in duckweed (Wolffia and Lemna genera) when the ash content is analysed. The micronutrient content of duckweed not only depends on the genetic characteristics of the species but also on the cultivation conditions. Duckweeds are known to accumulate large amounts of minerals in their tissues.
3.6 Polyphenols, Flavonoids, and Secondary Metabolites
High levels of polyphenols and flavonoids (rutin and quercetin) have been identified in duckweed. Common duckweed (Lemna minor) is a rich source of carotenoids and total flavonoids (mainly flavones and flavonols), followed by phenolic acids, low-molecular-weight phenolics, and glucosinolates. Studies of Wolffia globosa have correlated its free-radical scavenging capacity with beta-carotene, ferulic acid, luteolin-7-O-β-D-glucoside, and kaempferol phytochemical contents.
Bioactive compounds such as α-tocopherol, vitamin E, phytosterols, and carotenoids are richly present in duckweed; these compounds are known to be biologically active by having antioxidative, anti-inflammatory, and anti-cancer properties, which are essential for promoting human health. In one study of fresh Wolffia globosa, crude protein (29.84%), crude lipid (5.77%), total carotenoids (722.8 μg/g), and vitamin C (70.02 mg/100 g) were quantified, alongside total phenolic content (191.47 mg GAE g−1 dry weight) and total flavonoid content (91.54 mg QE g−1 dry weight).
3.7 Antinutritional Factors
Regarding antinutritional factors in Wolffia globosa powder, phytic acid was found below the limit of detection (<0.14%) in six batches, and oxalic acid was measured between 230 and 637 mg/100 g in nine batches. In Lemna and Spirodela, high fiber, tannin, and ash contents can reduce amino acid digestibility. Fermentation has been shown to reduce these antinutritional factors: after fermentation with Bacillus sp., the fiber content of duckweed leaf meal reduced from 11.0% to 7.5%, and the antinutritional factors tannin and phytic acid were reduced from 1.0% to 0.02% and 1.23% to 0.09%, respectively.
4. Established and Proposed Mechanisms of Action
4.1 Protein Nutrition and Essential Amino Acid Supply
Duckweed proteins contain all nine essential amino acids in a complete profile. Lemnoideae demonstrate a favorable amino acid profile, high digestibility, and low allergenic potential. The protein digestibility-corrected amino acid score (PDCAAS) of 89% for the Mankai strain compares favorably with many plant protein sources and supports its utility as a dietary protein supplement.
4.2 Vitamin B12 Bioavailability
Unlike most plant foods, which contain no or only inactive corrinoid analogs, Wolffia globosa contains authentic, bioavailable forms of cobalamin. Cobalamin (vitamin B12) content was examined in a cultivated strain of Wolffia globosa (Mankai), and predicted functional pathways were assessed using a gut bioreactor; the effects of long-term Mankai consumption as a partial meat substitute on serum B12 concentrations were explored in the 18-month DIRECT-PLUS weight-loss trial using microbiological assay and LC-MS/MS. The B12 content of Mankai was consistent at different seasons (p = 0.76).
4.3 Antioxidant Activity
Laboratory assays (DPPH, FRAP, ABTS, TPC, and TFC determinations) confirmed the strong antioxidant activity of Wolffia globosa, Wolffia arrhiza, and Lemna minor, which is attributed to their high content of phenols, flavonoids, and carotenoids. Total flavones, total flavonols, and total carotenoid equivalents showed the highest and most positive correlation values with the bioactive properties measured in Lemna minor.
4.4 ACE Inhibition and Antihypertensive Peptides
Protein hydrolysates of duckweed exhibited strong inhibitory activity against the angiotensin-converting enzyme (ACE), highlighting their antihypertensive potential, as well as activity against other metabolic enzymes, suggesting a broad spectrum of bioactive effects. Duckweed (water lentil) was investigated as a source of bioactive peptides; the chymotryptic final hydrolysate, the chymotryptic supernatant, and the papain supernatant increased the ACE inhibitory activity by more than 6- to 8-fold, resulting in IC50 values ranging between 0.55 to 0.70 mg peptides/mL. Depending on the fraction, the ACE inhibition was attributed to either bioactive peptides, phenolic compounds, or a synergistic effect of both. This research is currently limited to in vitro biochemical studies; no human clinical trials have specifically tested duckweed-derived ACE inhibitory peptides for blood pressure lowering.
4.5 Prebiotic and Gut Microbiome Modulation
Simulated digestion of Wolffia globosa confirmed its prebiotic properties. In an in vitro batch culture model of the proximal colon, Mankai significantly stimulated the production of phenolic metabolites and short-chain fatty acids by the gut microbiota (p < 0.05). Three major microbial metabolites — 3-4-hydroxyphenyl propionic acid, 3-3-hydroxyphenyl propanoic acid, and protocatechuic acid — were significantly increased after 24 h fermentation. Mankai treatment lowered the overall microbial diversity, in line with a selective microbiome modulation. These findings are in vitro only and require confirmation in human trials.
4.6 Glycemic and Metabolic Effects
Protein hydrolysates of duckweed exhibited activity against metabolic enzymes, suggesting a broad spectrum of bioactive effects including antihypertensive potential. Its nutritional composition not only helps control lipid and glycemic profiles, but also reduces inflammation and protects blood vessels, making it a promising ingredient in the nutrition of people with cardiovascular diseases. These mechanistic claims are primarily supported by in vitro and animal data; the precise mechanisms mediating human metabolic effects observed in clinical trials have not been fully elucidated and are likely multifactorial.
5. Scientific Evidence by Area of Use
5.1 Protein Bioavailability (Human Clinical Trial)
While the world is extensively looking for alternatives to animal protein sources, Wolffia globosa is an aquatic, edible duckweed that offers all nine EAAs, dietary fibers, polyphenols, iron, zinc, and B12 vitamin. This work was designed to evaluate Mankai (a newly developed high-protein strain of W. globosa) as an optional bioavailable source of EAAs for humans (primary outcome), and of further nutrients such as vitamin B12, in comparison to well-established animal and plant protein sources; cheese and peas, respectively. 36 men, subjected for 3 days to a stable diet and subsequent overnight (12 h) fast, were randomized to consume one of three iso-protein (30 g)-based test meals.
Evidence strength: A small (n = 36) randomized controlled trial in healthy men. The study demonstrated Mankai's protein bioavailability but was conducted by a research group with industry ties (Hinoman Ltd.), employed a single-sex population, and was limited to a short acute-exposure design. Findings support protein bioavailability but should be viewed as preliminary.
5.2 Postprandial Glycemic Response (Human Clinical Trial)
In 2019, investigators reported that among non-diabetics and those with fasting glucose levels within the normal range, consuming a Mankai smoothie in the evening led to lower glucose levels after the meal and lower fasting overnight compared to a yogurt smoothie. Among non-diabetics and those with fasting glucose levels within the normal range, consuming a Mankai smoothie in the evening led to lower glucose levels after the meal and lower fasting overnight compared to a yogurt smoothie. The investigators now plan to explore the effect of Mankai daily supplementation on post-meal glycemic response in participants with type 2 diabetes.
Evidence strength: This glycemic finding originated as a secondary or exploratory observation within a larger trial (DIRECT-PLUS). A dedicated randomized controlled trial specifically in type 2 diabetic patients has been registered (NCT06416475 / NCT04945109) but published results were not available at the time of this article. Evidence for glycemic benefit in diabetic populations remains pending.
5.3 Liver Fat / Non-Alcoholic Fatty Liver Disease (Human RCT — DIRECT-PLUS Trial)
The most substantive human clinical evidence comes from the DIRECT-PLUS trial, an 18-month, three-arm randomized controlled trial conducted in Israel. For the DIRECT-PLUS 18-month randomized clinical trial, 294 participants with abdominal obesity/dyslipidemia were assigned into healthy dietary guidelines (HDG), MED, and green-MED weight-loss diet groups, all accompanied by physical activity. Both isocaloric MED groups consumed 28 g/day walnuts (+440 mg/day polyphenols provided). The green-MED group further consumed green tea (3–4 cups/day) and Mankai (a Wolffia globosa aquatic plant strain; 100 g/day frozen cubes) green shake (+1240 mg/day total polyphenols provided). Intrahepatic fat (IHF%) 18-month changes were quantified continuously by proton magnetic resonance spectroscopy (MRS).
Despite similar moderate weight loss in both MED groups, the green-MED group achieved almost double IHF% loss (−38.9% proportionally), as compared with MED (−19.6% proportionally; p = 0.035 weight loss adjusted) and HDG (−12.2% proportionally; p < 0.001). Overall, NAFLD prevalence declined to: 54.8% (HDG), 47.9% (MED), and 31.5% (green-MED) (p = 0.012 between groups).
Greater IHF% loss was independently associated with increased Mankai and walnuts intake, decreased red/processed meat consumption, improved serum folate and adipokine/lipid biomarkers, and changes in microbiome composition (beta-diversity) and specific bacteria (p < 0.05 for all).
Evidence strength: The DIRECT-PLUS trial is a well-designed, 18-month randomized clinical trial with objective MRS-based liver fat measurements. However, Mankai was consumed as part of a complex dietary intervention (Green-MED diet) that also included restriction of red/processed meat and daily green tea and walnuts. The independent contribution of Mankai cannot be isolated from the overall dietary pattern. Confounding by the polyphenol-rich dietary pattern, single-site location (predominantly male workforce cohort), and commercial affiliation are acknowledged limitations.
5.4 Gut Microbiome Modulation (Human RCT — DIRECT-PLUS Secondary Analysis)
The DIRECT-PLUS dietary trial was a three-armed randomized trial including 294 subjects. In a secondary analysis, investigators evaluated the effect of MED-based dietary interventions on the gut microbiome composition and function, identifying specific microbial genera and metabolic pathways modified by the plant-enriched Green-MED diet. Main conclusions from the DIRECT-PLUS trial refer to the beneficial effect of the green-Mediterranean diet on cardiometabolic risk, gut bacteria, and liver fat, with no evidence of disadvantages or adverse effects of long-term Mankai consumption.
Evidence strength: Secondary analysis of a larger RCT; unable to attribute microbiome changes specifically to Mankai. In vitro fermentation studies support prebiotic potential but cannot substitute for adequately powered, dedicated human trials.
5.5 Vitamin B12 Status (Human Evidence — DIRECT-PLUS Substudy)
The presence of B12 in the cultivated Mankai strain was examined using LC/ESI-tandem-mass-spectrometry (LC-MS/MS) and anoxic bioreactors; the effect of a green Mediterranean/low-meat diet containing 100 g of frozen Mankai shake/day on serum B12 levels was explored during the 18-month DIRECT-PLUS weight-loss trial, compared with control and Mediterranean diet groups. In one human experiment, processed W. globosa was reported to provide dietary protein and vitamin B12.
Evidence strength: One clinical study has verified the presence and bioactivity of vitamin B12 forms in Mankai using rigorous LC-MS/MS methodology. Human serum response data from the DIRECT-PLUS cohort are available, though the dietary intervention is multicomponent. This is among the most compelling single-nutrient findings for duckweed as a novel food.
5.6 Cardiovascular and Lipid Biomarkers (Human Evidence)
Within the DIRECT-PLUS framework, the Green-MED group showed favorable lipid profile changes. The LDL-C/HDL-C ratio decline was greater in the green Mediterranean group than in other groups. Higher and similar weight reductions were observed, following a caloric deficit, in the two MED groups (MED: −2.9 ± 5.2%; Green-MED/low-meat: −3.9 ± 6.5%) compared with the HDG group (−0.6 ± 5.1%, p < 0.05 for both MEDs vs. HDG).
Evidence strength: Cardiovascular biomarker improvements in human trials are observed as part of the Green-MED dietary pattern rather than isolated to duckweed alone. No standalone duckweed RCT for cardiovascular endpoints has been published.
5.7 Antimicrobial Properties (In Vitro Only)
Extracts of Lemna minor demonstrated antibacterial activity against numerous Gram-positive and Gram-negative bacterial strains as well as yeasts. Among protein fractions from Wolffia globosa, the protein hydrolysate fraction (PCH) exhibited antimicrobial properties by decreasing populations of Vibrio parahaemolyticus and Candida albicans. These findings are entirely in vitro and have no direct human health application established to date.
5.8 Antioxidant and Anti-inflammatory Activity (Primarily In Vitro)
DPPH, ABTS, and FRAP assays demonstrated higher sensitivity in boiled Wolffia globosa filtrates, especially in the DPPH and FRAP tests, likely due to an increased release of compounds resulting from heat treatment. This was supported by a positive correlation between phenolic content and antioxidant activities, highlighting the importance of flavonoids among the phenolic compounds. These are in vitro antioxidant assays; their clinical relevance in humans requires further investigation through appropriately designed trials.
5.9 Cytotoxicity and Cell Safety Studies
Extracts from seven duckweed species — Spirodela polyrhiza, Landoltia punctata, Lemna gibba, Lemna minor, Wolffiella hyalina, Wolffia globosa, and Wolffia microscopica — covering all five genera of the plant family were tested for cytotoxic effects on human cell lines HUVEC, K-562, and HeLa. Duckweeds did not possess any detectable anti-proliferative or cytotoxic effects, and the present result is a first step to exclude any harmful effects of highly nutritious duckweed for human consumption.
6. Body Systems and Health Areas Associated with Duckweed
- Protein / Musculoskeletal Nutrition: Complete essential amino acid profile supports general protein nutrition for vegans, vegetarians, and elderly populations with elevated protein requirements.
- Hepatic Health: Preliminary human evidence (DIRECT-PLUS) associates Green-MED dietary patterns inclusive of Mankai with reduced intrahepatic fat and lower NAFLD prevalence.
- Metabolic / Glycemic Health: A crossover study observed lower postprandial and overnight glucose when Mankai smoothie was consumed versus yogurt. Ongoing clinical trials target type 2 diabetes populations.
- Cardiovascular Health: Protein hydrolysates exhibited strong inhibitory activity against ACE, highlighting antihypertensive potential. Lipid biomarker improvements observed in the DIRECT-PLUS trial as part of Green-MED dietary pattern.
- Gut Health / Microbiome: In vitro fermentation with gut microbiota demonstrated that Mankai significantly stimulated the production of phenolic metabolites and short-chain fatty acids, with three major microbial metabolites significantly increased after 24 h fermentation.
- Hematological / B12 Nutrition: Potentially significant for vegans and vegetarians given verified bioactive cobalamin content with absence of pseudo-B12 analogs.
- Antioxidant / Inflammation: High phenolic and flavonoid content supports in vitro antioxidant activity. Human relevance not yet established through dedicated clinical trials.
7. Dosage Forms and Dosages Reported in Studies
The following dosages appear in peer-reviewed or registered clinical research. These are study-specific doses and should not be interpreted as established therapeutic recommendations.
- 100 g/day frozen cubes (as Mankai green shake): In controlled dietary interventions, Mankai has commonly been provided as approximately 100 g frozen biomass/day blended into a "green shake." This dose was used in the 18-month DIRECT-PLUS trial.
- Iso-protein test meal (30 g protein): In the protein bioavailability RCT, 36 participants were randomized to consume equivalent protein (30 g) content from one of three whole food items — white cheese, green peas, or Wolffia globosa (Mankai) intact, cooked — consumed in the morning following a 12 h fast.
- Powder form: Mankai (Wolffia globosa) is usually presented in powder form or as frozen cubes for smoothies. Specific powder dosages in human supplement trials are not yet standardized in the published literature.
8. Safety Considerations
8.1 General Safety Profile
Duckweeds possess good qualitative and quantitative profiles of nutritional components for use as human food; however, studies specifically examining the probable presence or absence of adverse effects have been limited. The main conclusions from the DIRECT-PLUS trial refer to the beneficial effect of the green-Mediterranean diet on cardiometabolic risk, gut bacteria, and liver fat, with no evidence of disadvantages or adverse effects of long-term Mankai consumption.
8.2 Heavy Metal and Contaminant Accumulation
This is the most clinically significant safety concern associated with duckweed as food. The European Food Safety Authority (EFSA) has remarked that heavy metals and microcystins can accumulate in the culture medium; the presence of these elements in fresh plants should be controlled. Trace elements may also come from the use of fertilizers in the cultivation of Wolffia, which can be a safety concern for consumption.
The Commission specified maximum safety limits for heavy metals (lead: <0.3 mg/kg; arsenic (inorganic): <0.10 mg/kg; cadmium: <0.2 mg/kg; chromium: <1 mg/kg; mercury: <0.10 mg/kg), trace elements (copper: <0.8 mg/kg; molybdenum: <0.3 mg/kg; zinc: <5 mg/kg; boron: <5 mg/kg; manganese: <6 mg/kg), and cyanotoxins (microcystins: 0.006 μg/g). The fresh plants of Wolffia arrhiza and Wolffia globosa can be marketed as long as they comply with these criteria.
Wolffia globosa grown in contaminated water could be of concern as this plant species has shown significant uptake and accumulation of cadmium, arsenic, and chromium. For this reason, Wolffia globosa has been considered as having potential for phytofiltration of contaminated water and paddy soil.
8.3 Manganese Safety Concern for Powdered Forms
In a prior EFSA scientific opinion on water lentil powder from Lemnaceae, the Panel concluded that the increase in manganese intake from the novel food was substantial as compared to the background manganese dietary intake, and consequently, the safety of the novel food powder could not be established. EFSA concluded that an increase in manganese intake from this novel food used as a food ingredient or food supplement is of safety concern. Therefore, at that time, both Wolffia species are only commercially available as fresh plants (vegetables).
8.4 Cyanotoxin Risk
In batch testing for the Wolffia globosa powder novel food application, cyanotoxins — including anatoxin (LOQ: 10 μg/kg), microcystins (LOQ: 25 μg/kg), and nodularin (LOQ: 25 μg/kg) — were all reported below the quantification limit in three batches. This risk is nonetheless real for duckweed harvested from natural or contaminated water bodies.
8.5 Oxalic Acid
Oxalic acid was measured between 230 and 637 mg/100 g in nine batches of Wolffia globosa powder. Individuals with a history of oxalate kidney stones should exercise caution; however, this oxalic acid content is comparable to many commonly consumed leafy vegetables. In contrast to other duckweed species, Wolffia globosa does not contain high levels of calcium oxalate crystals.
8.6 Vitamin K Content and Potential Drug Interaction
In a safety assessment by the EFSA Panel on Nutrition, Novel Foods and Food Allergens, Wolffia globosa powder contained phylloquinone (vitamin K1) concentrations of 2–12 mg/100 g. This level of vitamin K is substantial and could theoretically interact with vitamin K antagonist anticoagulants such as warfarin, though specific pharmacokinetic interaction studies with duckweed have not been published.
8.7 Drug Interactions
Drug interactions with Mankai have not been well studied. Given the high vitamin K content, the mineral-accumulating properties, and the potential gut microbiome-modulating activity of duckweed, individuals on anticoagulant, immunosuppressant, or other sensitive medications should be aware that systematic interaction data are lacking.
8.8 Allergenicity
Lemnoideae demonstrate a favorable amino acid profile, high digestibility, and low allergenic potential. Wolffia is gluten-free and does not contain the most common allergenic proteins, so it should be regarded as hypoallergenic. However, formal allergenicity testing in human populations remains limited.
8.9 Genotoxicity and Subchronic Toxicity
A genotoxicity and repeated-dose toxicity evaluation of dried Wolffia globosa Mankai was conducted (Kawamata et al., 2020, Toxicology Reports) and was cited in the EFSA novel food dossier. The EFSA Panel notes that the concentration of trace elements and contaminants in the novel food is highly dependent on the conditions of cultivation of the plant and the fertiliser composition. The EFSA safety assessment concluded that, with cultivation under controlled conditions and adherence to specified maximum contaminant limits, the fresh plant material is safe for consumption by the general population.
9. Summary of Evidence Strength
The current evidence base for duckweed as a dietary supplement and functional food is emerging but still limited in human clinical data. The most robust human evidence comes from the DIRECT-PLUS trial series, which employed Mankai as one component of a complex dietary pattern, making it difficult to attribute observed health outcomes specifically to duckweed. The protein bioavailability RCT (n = 36) and the vitamin B12 LC-MS/MS characterization represent solid preliminary human-level findings. Claims regarding antihypertensive, antimicrobial, anti-inflammatory, glycemic, and microbiome effects rest predominantly on in vitro biochemistry and secondary analysis of multi-arm dietary trials. The studies indicate that the health-promoting properties of duckweed have been evaluated in diverse experimental models — ranging from in vitro analyses, through animal experiments, on to clinical trials involving humans. Independent, adequately powered, pre-registered human trials are needed to confirm most proposed health benefits of duckweed consumed as an isolated supplement.
References
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