Review on edible water lilies and lotus: Future food, nutrition and their health benefits

The major reasons for the low utilization of edible aquatic plants are lack of enough information regarding the nutritional value, cultivation, production, harvesting, processing and their food preparation techniques. These plants are neglected by agri-business, researchers, policymakers, investors and development practitioners (Rampa et al., 2020). The cultivable aquatic food crops are lotus, water lily, Euryale and water chestnut (Jana et al., 2019). Water lilies and lotus can grow, develop and produce seed. Naturally, lotus and water lilies grow with seeds in soil and water in paddy field (Rusmayadi & Khairina, 2015). Lotus grows under tropical and sub-tropical climate. The distribution mapping of N.pubescens was reported, it grows best at water depth (35-121 cm), a light penetration depth (23-100 cm), a water pH (6.25-8.37), and a sediment pH (3.33-4.69) (Yuliarti et al., 2022). The cultivation of lotus requires heavy, muddy and soil rich in organic matter. In Vietnam, lotus cultivation gained popularity and emerged as alternative to rice receiving attention from national and international actors (Vo et al., 2021). Lotus and water lilies grow easily in ponds, whiskey barrel or planter. The agronomic practices of lotus cultivation, propagation methods, planting distance, fertilizer application and yield quantity per hectare were reported (Jana, 2019). Lotus plant can propagate through seed/plantlet, planting distance (1 m x 1 m), fertilizer N: P: K (kg/ha) in the ratio of 100:60:40 and yield 1.5 ton per hectare (Jana et al., 2019). As similar to lotus, water lily can grow in ponds, lakes and perennial water bodies in all types of climate. Water lilies can propagate through either corm or seed. The ideal soil for water lily cultivation is soil rich organic matter. The plant need planting space of 1 m x 1 m, an ideal fertilizer rate of N: P: K (60:40:30) for growth and development, yield 25 tons per hectar (Jana, 2019). The study on the productivity of hairy water lily (N. pubescens) in Paharangan, Hambuku and Ampukung districts of Indonesia was reported that the water lily seeds were 0.653 t/ha, 1.057 t/ha and 1.121 t/ha, respectively (Rusmayadi & Khairina, 2015).

The rhizome of water lilies and lotus can be plucked from muddy or sand of water shore that can be either boiled or raw sliced, dried, grounded and finally combined with other grains to make different value added food products. Seedpods of water lilies and lotus can easily hand picked as the matured seedpods submerge in the water. The poppy seeds of water lilies are harvested from the pods. Inventing new technologies for the production, processing, and marketing of water lilies and lotus is crucial for increasing productivity of these aquatic crops (Jane, 2019).

The presence of high content of essential amino acids in the seeds of N. lotus satisfies the recommended value by WHO/FAO (0.8 g/kg of body weight per day) (Danhassan et al., 2018). The seed of water lily can supply essential amino acids required for the growth and development in a superior way to other protein containing foods. The non-essential amino acids are a component of glutathione and precursor of gamma amino butyric acid which is neurotransmitter (Danhassan et al., 2018). The presence of all essential amino acids could make this rhizome of water lily as a food supplement for human(Chinelo & Jega, 2019) . The essential amino acids content of red and green seeds of N.lotus is higher than some common cereals consumed in Nigeria. The lysine content of N.lotus is as comparable to the values of maize and wheat higher than pearl millet, acha and sorghum. The methionine content of N.lotus seeds is higher than the value for wheat, maize, sorghum and millet (Laminu et al., 2021). The seeds of N.lotus and N. pubescens could meet up with the WHO ideal protein value for both children and adults. The level of arginine and histidine in the seeds warrants them to be recommended for children food since children need arginine and histidine in their foods (Aliyu et al., 2017a).

Dietary fiber either soluble or insoluble has positive effects to prevent constipation, regulate serum cholesterol level, maintain body weight, reduce the risk of diabetes, intestinal cancer and stimulate beneficial bacteria. The soluble and insoluble dietary fiber of N.lotus seed was reported to be 4.68% and 8.54% (Danhassan et al., 2018). The dietary fiber content in the Nymphaea spp. seeds is comparable to rice and millet that are important in the diets of population all over the world (Gueye et al., 2020). Tuber of N.nouchali is an economical dietary adjunct and functional food with significant macro and micro nutrient that can help fight against oxidative stress originating due to modern life style induced metabolic disorders (Anand et al., 2019). Meat nuggets supplemented with 3% root powder of N.nucifera was reported to have better potential source of dietary fibers (Verma et al., 2022).

Food containing high potassium content is very suitable for hyperglycemic patients. The potassium content of seed or rhizome of different nymphaea species is higher as compared to other minerals. The highest amounts of potassium 870 mg/100 g and 981.29 mg/100 g was found in N.nouchali and N.rubra respectively. The presence of high potassium helps the body to maintain water balance in the muscles and nerve cells. Calcium, the elements that is important to regulate muscle and heart function, transmission of nervous system, formation and maintenance of bones and teeth was reported to be found in higher amounts in red and green seed of N.lotus as compared to maize, wheat, sorghum and pearl millet. Generally, the rhizome of N.lotus contains low sodium and high potassium which suggested it good source of food for hyperglycemic patients. Hence, the rhizome of N.lotus could serve as ingredient in food formulation and pharmaceutical industries (Wasagu et al., 2015).

Adequate supply of omega 6 and 3 is a crucial to maintain the health of cardiovascular system. Generally, a food containing 1:1 to 5:1 ω-6: ω-3 ratio is considered optimal for human health (Patel et al., 2022). The management of chronic diseases depends on the availability of essential fatty acids such as linoleic acid, linolenic acid, and others supplied from foods. In this regards the rhizome of N.nouchali is in close proximity to the above suggestion that makes N.nouchali rhizome an ideal source of balanced dietary essential fatty acids (Anand et al., 2019). Anand et al. (2019) observed that N.nouchali as a rich source of dietary oleic acid. Similarly the seeds of N.lotus and N.pubescens were reported to possess good source of fatty acids (Aliyu et al., 2017b). The seeds of N.alba were reported to contain linoleic acid (37.5%) and oleic acid (10.9%) (Nengroo & Rauf, 2020). Compared to ω−3 or ω−6 fatty acids, dietary oleic acid is more resistant to oxidative stresses and provides protection against damage to cell membranes caused by free radicals. Oleic acid-rich diets are said to help hypertension individual's high-density lipoprotein cholesterol and reduce blood pressure. Dietary oleic acid has recently been demonstrated to lower inflammatory levels brought on by obesity.

Vitamins are required in trace amounts by our body for metabolism and physiological functions to prevent diseases such as those associated with oxidative stress. Rhizome of N.lotus contains significant amount of carotenoids equivalent (51.3 mg/100 g) and vitamin C (24.65 mg/100 g) (Stephen et al., 2017). In another study conducted by Anand et al. (2019) boiled rhizome of water lily has 3.12 mg/100 g of ascorbic acid, 1.11 mg/100 g of riboflavin, 0.05 mg/100 g of thiamine and 1.45 mg/100 g of niacin. Green and red seed of N.lotus was found to contain higher riboflavin and thiamin contents than the values reported in maize, wheat, sorghum, acha and pearl millet.

Seed and rhizome of water lily contains different fractions of carbohydrate. The major composition (50% dry weight) of lotus seed is starch (Dhull et al., 2022). The seed of lotus are important food item in many countries due to its low glycemic index food. Starch is an important source of dietary carbohydrates in human diet. However, the rapid digestion of starch allows the rapid rise in blood glucose which is looked upon negatively. Higher consumption of foods containing starch with low glycemic index is known to give better contribution to health particularly for those with obesity and diabetes mellitus 2. Resistant starch is not digested in the mouth, stomach, or small intestine but is fermented by microbial flora in the colon, which generates short-chain fatty acids that have potential health benefits. It has been observed that boiling of water lily seed reduces soluble sugars content (Danhassan et al., 2018). Accordingly, boiling of N.lotus seed was found to reduce glucose content from 0.77 mg/100 g to 0.44 mg/100 g, maltose from 1.31 mg/ 100 g to 0.84 mg/100 g and sucrose from 2.18 mg/100 g to 1.76 mg/100 g and fructose from 0.87 mg/100 g to 0.72 mg/100 g (Danhassan et al., 2018). Even though the rhizome contains high amounts of carbohydrate, boiled/freeze dried tuber of N.petersiana contains small quantities of water soluble sugars fructose 2.4 mg/100 g, glucose 3 mg/100 g and sucrose 0.05 mg/100 g. In addition to soluble sugars, ultrasonic-assisted extract of N.odorata mucilage possess polysaccharide called glucuronic (Zhi et al., 2018).

The extracts from water lilies and lotus are well recognized as a potential source of anti-oxidant. Methanol extract of boiled tuber of N.nouchali was reported to bear antioxidant phytochemicals that quench H₂O₂ which induce oxidative stress hence protect DNA against free radical-induced damage (Anand et al., 2019). Extracts of boiled rhizome have potent to scavenge free radicals and reduce starch induced postprandial glycemic through inhibition of α-glucosidase (Anand et al., 2021). In-vitro study conducted in Thailand on 95% extracts of water lily indicated that, the extracts was reported to had highest free radical scavenging activities as compared to l-ascorbic acid, α-amylase and α-glucosidase inhibition as compared to acarbose (Boonpisuttinant et al., 2019). The rhizome also possesses free radicals scavenging activities, reducing power and strong inhibitory activities against the formation of glycation end products which linked to oxidative stress and development of diabetes mellitus 2 (Priyanka, Anand, Bhargavi, Zehra, & Tiwari, 2016). Study conducted in Bangladesh indicate, the antioxidant properties IC₅₀ value of N.nouchali (36.67 µg/mL) and N. rubra (28.48 µg/mL) have higher than reference ascorbic acid (9.56 µg/mL). However, the extract from N.lotus flowers bears stronger antioxidants than α-tocopherol with IC₅₀ of 85% of inhibition of lipid peroxidation (Saleem, Ahotupa, & Pihlaja, 2001). The N.nouchali boiled rhizome (NNBR) extracts have strong free radical scavenging activities against nitro blue tetrazolium, FeCl3, hydroxyl, superoxide, nitric oxide and lipid peroxidation (Anand et al., 2021). Phenolic and flavonoids compounds extracted from leaf of N.lotus was found to be twice more potent in scavenging DPPH radicals as compared to butylated hydroxytoluene, six fold more potent to inhibit lipid peroxidation as compared to gallic acid with low cytotoxicity to liver cell line (N'guessan et al., 2021). The methanolic extract of N.lotus was reported to contain low IC₅₀ (0.016 mg mL⁻¹) indicating a good source of natural antioxidants (Ibrahim et al., 2020). The stamen of N. lotus was reported to possess flavonoids compounds that mediate electron transfer to act as antioxidant (Tungmunnithum et al., 2022). The antioxidant activity in N.antares water lily leaves and petioles is assumed to be affected by different extraction pH conditions. The polyphenols oxidase activity was reported to be higher at pH 7.1 in leaves extract whereas polyphenols oxidase and peroxidase was reported to higher at pH 7.8 and 7.1 (Mohd et al., 2022). The maturity stages of seed of N.lotus were reported to affect the antioxidant power. Black seeds N.lotus had strong antioxidant power (87.67%) as compared to seeds of N.micrantha (83.92%) and red seeds (86.63%) of N.lotus due to the synergistic action of phenolic, flavonoids and tannins (Gueye et al., 2022). The antioxidant power of water lilies and lotus can be different based on assays used. The DPPH, Lipid peroxidation, superoxide scavenging activities of ethanol extract of N.nouchali was reported to be 25.42, 23.33 and 49.66 (LC₅₀ (µg/ml)), respectively (Ramesh et al., 2022). The antioxidant properties of water lilies and lotus can also be affected by solvents used to extract the phytochemicals. The major solvents used to extract phytochemical are methanol, ethanol, ethyl acetate, acetone and water. The antioxidant properties of N.alba extracted using ethanol was shown to be stronger than the aqueous extract by inhibiting DPPH, hydroxyl radical, nitric oxide scavenging activities when compared to ascorbic acid. The aqueous and ethanolic extract of N.pubescens was reported to 375.4 g/mL (weak) and 56.4 g/mL (strong) IC₅₀ values, respectively (Chandra et al., 2022). The solvent concentration, extraction time and ratio of solid to solvent affect the amounts of phytochemical and antioxidant power of the constituents. Response surface methodology was used to optimize ethanol concentration, extraction time and solid to solvent ratio and reported that phenolic, flavanoid, DPPH and FRAP were 51 mg GAE/g, 27.3 mg CE/g, 29.6 mmol TE/g and 21.4 mmol TE/g, respectively (Prikboonchan & Samavardhana, 2021). The ethanol extract of N. lotus was reported to give greater protective effect to cell membranes of RBC hemolysed by 2, 2-Azobis (2-amiinopropne) dihydrochloride (Semaming et al., 2018). Afolayan et al. (2013) observed the acetone extract of N.lotus has lower IC₅₀ for DPPH (0.016 mg mL⁻¹) and nitric oxide (0.022 mg mL⁻¹) radical scavenging activity. However, aqueous extract of N.lotus has lower IC₅₀ for ABTS (0.04 mg mL⁻¹) radical scavenging activity (Afolayan et al., 2013). The ethyl acetate extract of N.lotus leave was reported to possess phenolic and flavanoids that donate electrons to free radicals (Mahmud et al., 2020). The phytochemical extracts that has lower IC₅₀ is known to possess higher antioxidant power. In this regard, the crude extract of N.pubescens was reported to possess good DPPH free radical scavenging properties (1.43 µg/mL) as compared to N.nucifera (3.52 µg/mL). Furthermore, N.pubescens was reported to possess better α-glucosidase inhibition activity, as implicated in lower IC₅₀ (5.29 µg/mL) as compared to N.nucifera (29. 06 µg/mL) (Nishan, 2020).

The rhizome of the water lily is a rich source of nutrients for eating, but because of the impact of some anti-nutritional composition, it is best advised that the bulb need to be processed by any other technique to remove the anti-nutritional content like phytates before consumption. The rhizome of water lily contains anti-nutrient like phytates (3.68 mg/100 g), oxalate (8.76 mg/100 g), tannins 13.63 (mg/100 g), and saponins 4.89 (mg/100 g). UV-VIS spectrophotometer analysis of acetone extract of N.lotus indicated the presence of anti-nutritional factors like tannins (64.7 mg/g), saponins (12.31 mg/g), alkaloids (0.86 mg/g) and steroids (21.62 mg/g) (Afolayan et al., 2013).

Study in female rats was indicated that, the ethanol extract of N.alba produced a dose related increase in the force of uterine contraction similar to oxytocin (Bose, Sahoo, Rout, & Si, 2014)

Study conducted in 40 male rats was indicated that, N.lotus (75 mg/kg) was suppressed the effects of erectile dysfunction induced by nitric oxide (Kameni et al., 2019). It was also indicated that N.lotus has double medicinal use, against erectile dysfunction and anxiety. Some species of water lilies (N.alba) contains nupharine and nymphaeine that has sedative and an aphrodisiac property.

Ethanolic extracts of N.lotus decrease pain sensation in mice (Aduema, Amah, Akunneh-Wariso, & Vidona, 2019). In another study, the crude leaf extracts of N.lotus was reported to possess anti-anxiety and antidepressant activities (Fajemiroye et al., 2018). The phytochemicals responsible for sedative and CNS depressant with mild anxiogenic effect from N.lotus were alkaloids, saponins, tannins, cardiac glycosides, flavonoids, and terpenoids (Folashade et al., 2021).

The methanolic extracts of bioactive constituent from N.lotus were reported to manage pain and inflammatory diseases (Rege et al., 2021). The high-resolution mass spectroscopic technique profiled secondary metabolites from N.nouchali that prevent oxidative stress stimulated diseases and disorders (Alam et al., 2021). Ethyl acetate fraction from N. hybrid was known to treat lipopolysaccharide inflammatory induced inflammation by blocking the activation of NF-κB and MAPKs pathways in RAW264 7 cells (Zhang et al., 2021).

The rhizomes and seeds of N.lotus reported to possess phytochemicals such as phenolic, flavanols, tannins, saponins, steroids, and proanthocyanidins that aid as effective antimicrobial (Adenola et al., 2021). The functional groups of phytochemicals in N.lotus extracted using water, ethanol and N-hexane were identified using Fourier transform infrared spectroscopy. These compounds are antimicrobial in nature, medicinal to human and animal diseases that are caused by multidrug resistant enteric bacteria (Jesse, 2020). Additionally, it was reported that N.lotus anthraquinones, alkaloids, terpenes, deoxy-sugar, and glycosides for controlling bacteria and fungi like Enterobacter spp., C.albicans and A.flavus responsible for middle ear infection. Moreover, Salisu and Nura (2022) reported the stem extract of N.lotus contains phytochemicals responsible for inhibiting the growth of Salmonella typhi and Enterococcus faecalis. The inhibition zone created by seed extracts for C.albicans, E.coli, S.aureus, and P.aeroginos were 19.3, 19.0, 15.7, and 19.7 mm, respectively (Anywar et al., 2014). Extracts from different parts of N.lotus were used to treat different bacteria and fungi. Ethanolic root extracts of N.lotus were reported to possess antimicrobials against multidrug resistance enteric bacteria (Adenola & Adeleke, 2021). Similar solvent (ethanol) was used by (Dissanayake & Bandaranayake, 2020) to extract bactericidal from N.nouchali. It was observed that 20 mg/mL and 100 mg/mL concentrations were bactericidal against E.coli and S.aureus respectively (Dissanayake & Bandaranayake, 2020). Gold nanoparticles (AuNPs) prepared using root extract of N.alba at Au/root extract (0.24), pH (7.8) and sonication time (40 min) were reported to possess high antimicrobial activities against S.aureus and E.coli with minimum inhibitory concentration value of 100 µg Au/mL and 200 µg Au/mL, respectively (Cudalbeanu et al., 2021).

Medicinal plants that possess phenolic acids, flavonoids, alkaloids, triterpenoids, diterpenoids, monoterpenoids, chromenes, capsaicinoids, curcuminoids, and anthraquinones are major phytochemicals that are heptoprotective (Das et al., 2022). Ethanolic extracts of N.alba revealed the presence of phytoconstituents like phenolic, alkaloids, glycosides, steroids, flavonoids and tannin. Isostrictinin isolated from N.candida was reported to be hepatoprotective (hepatic fibrosis) in mice induced by 10% CCl₄ (Dong et al., 2022). The leaf extract of N.nucifera was reported to be hepatoprotective at doses of 300 and 500 mg/kg against CCl₄ induced liver toxicity in rats (Huang et al., 2010). Ethanolic extract of N.alba (400 mg/kg) significantly reduce liver functions tests like serum glutamic-oxaloacetic transaminase, serum gluamic pyruvic transaminase, alkaline phosphatase, bilirubin and cholesterol level as compared to the control group (Paharia & Pandurangan, 2013). Rats feed at a dose of 250 mg/kg of N.lotus leaf extract twice for two weeks was reported to antagonize the liver damage induced by CCl₄ and aspirin (Usman et al., 2018).

Water lilies and lotus contain alkaloids important for bioactivities (Ren et al., 2019). Among the alkaloid, nymphayol (25, 26-dinorcholest-5-en-3b-ol) is the bioactive content in flower and leaf of N.stellata responsible to increase insulin levels in diabetic rat. The oral administration of nymphayol was reported to reduce blood glucose levels and stimulated pancreatic beta cells regeneration (Khyade, 2018). The ethyl acetate extract of lotus leaf (N.nucifera Gaertn.) had flavonoids that aid in reduction of blood glucose and hypoglycemic effect on streptozotocin induced diabetic mice (Rumanti et al., 2017). Rhizome of N.nouchali may become an important dietary supplement to reduce postprandial hyperglycemia and hyperlipidaemia, oxidative stress and can be considered as herbal therapeutics for the management of type 2 diabetes mellitus and obesity (Anand et al., 2021). These antihyperglycemic compounds can display strong inhibitory properties against intestinal α-glucosidase and pancreatic lipase and increase cellular glucose uptake activities. The inclusion of boiled rhizome of water lily into diabetics’ food were indicated to have several health benefits in managing hyperglycemia and resultant oxidative stress (Anand et al., 2021). Flowers of N.pubescens and N.nucifera were reported to possess antidiabetic activities (α-glucosidase inhibition) (Pokhrel et al., 2022). Similarly, the whole flower of N.lotus was reported to better food supplements and beneficial to diabetic patients (Chaiyawathanananthn et al., 2022). Nymphayol extracted from N.stellata is phytochemicals which has anti-diabetic properties was reported to improve damaged endocrine tissue and stimulates secretion of insulin in the β-cells (Raja et al., 2010). Phytochemical screening of lotus leaf extracts using ethyl acetate indicated the presence of flavonoids (150 mg/kg) that are responsible for the reduction of blood glucose on diabetic induced mice (Rumanti et al., 2017). The antidiabetic potential of N.nucifera and N.pubescens was compared. It was reported that N.nucifera, N. pubescens, and acarbose possessed IC₅₀ value of α-glucosidase inhibition activity of 66.32 µg/mL, 5.29 µg/mL, and 5.65 µg/mL, respectively (Pokhrel et al., 2022). Nymphaea species are effective aquatic plants to inhibit glycation end products and type II diabetes mellitus (Ishrat et al., 2021). Specifically, N.stellata was reported to possess anti α-glucosidase and α-amylase activities (Chaiyawathanananthn et al., 2022). Moreover, seven different water lilies species were reported to possess antihyperlipidemic, antihyperglycemic, glucose uptake and metabolizing protein expressing, pancreatic β cell-regenerating, insulin secretion, sensitivity promoting, and intestinal glucose metabolizing enzyme inhibiting (Prodhan & Mridu, 2023).

Aqueous and ethanol extracts of N.lotus was reported to ameliorate neurotoxin induced seizures by enhancing the inhibition of Gamma aminobutryric acid neurotransmitter. The extracts also prevented kainic acid induced anxiety, depression and amnesia in mice (Ishola et al., 2022). Similarly, alcohol extract of N.indica possesses phytochemicals for treatment of epilepsy (Madhavan et al., 2009).

Traditionally the rhizome of N.lotus is used to cure diarrhea. Methanolic extracts of the rhizome of N.lotus was reported to have anti-diarrhoeal properties (Bello et al., 2016).

The in vitro studies on breast cancers, ovarian and prostate cancer cells indicated that, extracts of water lilies and lotus possess phytochemicals that can play significant role in cancer prevention. The ethanolic extract of N.nouchali was reported to shown superoxide scavenging, DPPH, lipid peroxidation and exhibit significant IC₅₀ values against MCF-7 cells (Ramesh et al., 2022). The ethanolic flower extracts of N.pubescens was reported to be cytotoxic against human breast carcinoma MCF and cervical carcinoma Hela cell lines with IC₅₀ value of 91.57 µg/mL and 99.6 µg/mL respectively (Selvakumari, Shantha, Purushoth, & Sreenathkumar, 2012). Whereas, the methanolic root and leaf extract of N.alba is promising against MCF-7 breast cancer, A2780/A2780cisR ovarian, and LNCaP prostate cells (Cudalbeanu et al., 2019). The same author was confirmed that, gold nanoparticles prepared using ultrasonic irradiation at Au/root extract ratio of 0.24, pH 7.8 and 40 min from root extracts of N. alba inhibit A2780 ovarian cancer cells by 50% at 51.9 µg Au/mL and 33.5 µg Au/mL concentrations (Cudalbeanu et al., 2021). Nymphayol (17-(hexan-2-yl)−10, 13-dimethylhexadecahydro1H-cyclopenta[a]phenanthren-3-ol) isolated from N.stellata was confirmed to inhibit MCF-7 breast cancer cells viability up to 78%, and the IC₅₀ value was observed as 2.8 µM in 24 h and 1.4 µM in 48 h (Al-Harbi et al., 2020).