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OPEN
Nutritional value, antioxidant and
antidiabetic properties of nettles
(Laportea alatipes and Obetia
tenax)
Nomfundo Thobeka Mahlangeni , Roshila Moodley
✉ & Sreekantha Babu Jonnalagadda
Nettles are commonly consumed in South Africa, Europe and Asia and are used in traditional medicine
to treat a variety of ailments. In this study, the nutritional value of the leaves of nettles (Laportea
alatipes and Obetia tenax) was evaluated and compared, when cooked and uncooked. The results
showed a decrease in the concentrations of crude protein, vitamin A, vitamin E and metals after
cooking of nettles. Although cooking reduced the concentrations of essential elements in nettles,
their contribution to the diet remained adequate. L. alatipes presented with reduced levels of Cd
(from 1.86 to 0.810 mg kg−1) and Pb (from 2.87 to 1.88 mg kg−1) after cooking. Similarly, Cd (from
2.97 to 0.780 mg kg−1) and Pb (from 2.21 to 0.795 mg kg−1) levels in O. tenax decreased after cooking,
demonstrating the significance of cooking. The antioxidant activity of the nettles was determined using
the 2,2-diphenyl-l-picrylhydrazyl (DPPH) free radical and ferric reducing antioxidant power (FRAP)
assays. The methanol extract of Obetia tenax showed high ferric reducing power whilst the radical
scavenging activity was due to the presence of the bioactive molecule, β-carotene, in the plants which
exhibited higher DPPH radical scavenging ability relative to test samples and standards. The in vitro
antidiabetic activity of the extracts and compounds from the nettles was better than or comparable
to that of the known standard, acarbose, which underscores the prospective antidiabetic properties
of nettles. Overall, our study provides scientific validation for the ethno-medicinal use of nettles and
supports their consumption, which highlights their potential as nutraceuticals.
Malnutrition results from inadequate intake of food or an improper diet and it affects normal functioning of the
human body as well as growth and development in children1. Malnutrition is a serious health concern in developing countries such as Asia, Africa, Latin America and the Middle East with one in five people being malnourished
and experiencing the conditions associated with micronutrient deficiencies2. For proper nourishment, the human
body needs foods rich in macronutrients (carbohydrates, fats, proteins and vitamins) and minerals but low in
sugar. In South Africa, non-communicable diseases (NCDs) such as cardiovascular disease, chronic respiratory
disease and cancer account for 37% of deaths. The World Health Organization (WHO) has therefore suggested a
daily intake of 400 g of fruits and vegetable per day to reduce the risk of NCDs3,4.
Food insecurity also plays a role in malnutrition as nutritious foods are inaccessible, unaffordable or unavailable. Leafy green vegetables are important in developing countries because they are cheap, readily available,
nutritious and easy to cook. These leafy green vegetables contain substantial amounts of antioxidant vitamins
(β-carotene, vitamin C and E) and minerals5.
Diabetes mellitus is a metabolic disorder characterized by hyperglycemia (high blood glucose) resulting in
defects in the secretion of insulin, impaired action of insulin or both6. In the absence of insulin, glucose (from
broken down carbohydrates and starch) builds up in blood vessels as it cannot be absorbed into the cells of the
body which results in organ and tissue failure. The International Federation of Diabetes (IDF) reported that
about 15.9 million have diabetes in Africa, and expected to increase by more than 100% in 20457. South Africa is
amongst the top five countries with the highest number of people living with diabetes7.
The growing popularity of nutraceuticals has led to a greater demand for the identification of new plants
that are both nutritional and medicinal. Laportea alatipes Hook. f. and Obetia tenax (N.E.Br.) Friis are from the
School of Chemistry and Physics, University of KwaZulu-Natal, Durban, South Africa. ✉e-mail: moodleyrosh@ukzn.
ac.za
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Laportea alatipes
UC
Obetia tenax
C
UC
DRI
C
(mg kg−1)
b
c
RDA (mg
per day)
DV
(mg)
L. alatipes
O. tenax
L. peduncularis
U. dioica
UC/C
UC/C
UC/C
UC/C
(mg per 60 g)
Macro-elements
Ca
34084 ± 1074ca
12652 ± 1598a
21999 ± 1618b
21620 ± 636b
1000–1300
1000
2045/759
1320/1297
1654/770
1899/871
Fe
57115 ± 6413c
39196 ± 5376a
112534 ± 9902d
16807 ± 2035b
8–18
18
3427/2352
6752/1008
78.7/60.6
12.5/19.1
Mg
12407 ± 432c
2023 ± 212a
10648 ± 544d
4075 ± 155b
240–400
400
744/121
639/245
420/142
371/136
P
1715 ± 108c
1264 ± 112a
1340 ± 74.6d
1135 ± 153b
1000
Micro-elements
Ba
77.0 ± 5.22b
57.7 ± 6.26a
151 ± 7.41c
88.1 ± 5.00b
Co
1.74 ± 0.26a
1.50 ± 0.19a
6.64 ± 0.430c
0.845 ± 0.118b
Cr
12.1 ± 1.32b
0.073 ± 0a
87.7 ± 6.11c
0.074 ± 0.001a
0.02–0.035
0.120
0.726/0.004
5.26/0.004
0.186/0.407
0.063/0.1
Cu
19.1 ± 1.02b
12.8 ± 0.59a
23.9 ± 2.01c
14.0 ± 0.86a
0.7–0.9
2
1.15/0.768
1.43/0.840
1.38/0.382
1.05/0.97
Mn
260 ± 18.2c
180 ± 24.9a
206 ± 14.3a
76.1 ± 3.34b
1.6–2.3
2
15.6/10.8
12.4/4.57
91.3/10.5
1.53/2.93
Ni
11.8 ± 0.95b
6.36 ± 1.39a
15.8 ± 1.04c
8.42 ± 1.19a
ND
0.708/0.382
0.948/0.505
0.287/0.121
0.144/0.03
Zn
60.7 ± 4.51c
50.9 ± 4.31a
34.3 ± 0.705b
35.2 ± 2.06b
8–11
3.64/3.05
2.06/2.11
2.25/1.51
1.9/1.6
15
Toxic elements
Cd
1.86 ± 0.207b
0.810 ± 0.168a
2.97 ± 0.177c
0.780 ± 0.167a
Pb
2.87 ± 0.250c
1.88 ± 0.134a
2.21 ± 0.128a
0.795 ± 0.157b
Table 1. Concentration (mg kg−1, mean ± SD, n = 4) of essential and toxic elements in L. alatipes and O. tenax
leaves (uncooked (UC) and cooked (C)). aValues in the same row with different letters are significantly different
(Tukey’s post hoc comparison, p < 0.05), bIndicates recommended dietary allowance14, cIndicates daily values20,
d
Results of previous study10. Dietary reference intakes (DRIs) (recommended dietary allowance (RDAs) and
daily values (DVs)) and average concentration (in mg per 60 g, dry mass, n = 4)) of essential elements in nettles
(L. alatipes, O. tenax, L. peduncularisd and U. dioicad).
Urticaceae (nettle) family and are known for their nutritional and medicinal value. These nettles are found in
KwaZulu-Natal, South Africa. They are generally known as forest nettle (L. alatipes) and mountain nettle (O.
tenax) or Imbati in isiZulu. In traditional medicine, nettles are used to treat conditions such as rheumatoid arthritis, gout, eczema, benign prostatic hyperplasia, anemia, influenza, asthma and diabetes8,9.
Previously, we reported on the distribution of nutrients and anti-nutrients in the nettles, L. peduncularis susp.
peduncularis and Urtica dioica10. In this study, we investigate the concentrations of nutrients and anti-nutrients
in the nettles, L. alatipes and O. tenax and compare these values to those obtained from our previously study. The
impact of cooking on nutritional value is also evaluated. Antioxidant and antidiabetic properties of the nettle
extracts and isolated compounds were also investigated.
Materials and Methods
The materials and methods section is presented as Supplementary Material 1.
Human and animal studies. This article does not contain any studies with human or animal subjects.
Results and Discussion
Elemental analysis.
On average, the moisture content of L. alatipes was found to be 79.2% and that of O.
tenax was found to be 82.1%. Food processing such as cooking alters the nutritional value of uncooked plant
foods. For this reason, both uncooked and cooked leaves of L. alatipes and O. tenax was investigated for essential
and toxic metal levels to determine their nutritional value and to assess for metal toxicities, respectively (Table 1).
Ingestion of toxic metals, even at low concentrations, can be detrimental to human health. Cadmium is known
to target the kidneys and respiratory system11, and long-term exposure to Pb may cause damage to the nervous system and can lead to blood disorders12. Subsequently, the joint Food and Agriculture Organization of the
United Nations (FAO) and WHO have set the maximum levels of Cd and Pb in leafy vegetables at 0.2 mg kg−1
and 0.3 mg kg−1, respectively13. In L. alatipes, Cd levels reduced by 56% from 1.86 to 0.810 mg kg−1 and Pb levels
reduced by 34% from 2.87 to 1.88 mg kg−1 whilst in O. tenax, Cd levels reduced by 73% from 2.97 to 0.780 mg kg−1
and Pb levels reduced by 64% from 2.21 to 0.795 mg kg−1, after cooking. This study shows concentrations of toxic
elements, Cd and Pb, to decrease significantly after cooking which indicates the benefits of cooking leafy vegetables to reduce metal toxicities.
The results in Table 1 also show the concentrations of elements in 60 g (suggested serving size which is equivalent to two cups of spinach) of L. alatipes, O. tenax (this study), and L. peduncularis and U. dioica and their contribution to recommended dietary allowances (RDAs) and daily value (DVs) for the studied essential elements10,14.
The estimated contribution to the diet by nettles can be used to assess for elemental value and deficiencies. Low
fruit and vegetable intake by individuals has been a major contributor to micronutrient deficiencies, as a result,
WHO has recommended consumption of a minimum of 400 g of fruits and vegetables per day15,16. Studies have
shown that the average consumption of vegetables is less than 80 g per day in South Africa16,17.
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Average concentration in uncooked/cooked leaves (g per 60 g, dry mass)
DRIa
LA
OT
LPb
UDb
RDA (g per
day)
DVc (g)
Carbohydrates
35.1/35.7
30.2/38.4
12.9/27.7
32.0/36.9
130
300
Proteins
3.22/2.94
3.20/3.11
0.82/1.07
0.89/1.10
34–56
50
Vitamin Ad
9.9 × 10−2/9.4 × 10−4
1.1 × 10−2/1.0 × 10−2
—
—
0.6 × 10−3–
0.9 × 10−3
0.7 × 10−3–
0.9 × 10−3
Vitamin C
0.023/0.022
0.023/0.023
0.011/0.010
0.013/0.010
0.045–0.075
0.06
Vitamin E
0.059/0.023
0.067/0.021
0.011/0.014
0.016/0.015
0.011–0.015
0.020
Table 2. Dietary reference intakes (DRIs) (recommended dietary allowances (RDAs) and daily values (DVs))
of macronutrients for most individuals and average concentrations of macronutrients (n = 4) in L. alatipes (LA),
O. tenax (OT) L. peduncularis (LP) and U. dioica (UD) leaves (uncooked/cooked). aIndicates dietary reference
intakes14. bResults of previous study10. cIndicates daily values20. dVitamin A as retinol; 1 µg β-carotene = 0.167 µg
retinol.
For the macro and micro-elemental content, the results showed a decrease in L. alatipes and O. tenax after
cooking (Table 1). The most common elements that are deficient in humans are Fe, Zn and Cu18. Disorders associated with Zn deficiencies include epilepsy, diabetes, multiple sclerosis, sickle-cell anemia and mood disorders.
Insufficient dietary intake of Cu can lead to impaired Fe metabolism with hypochromic anemia and bone abnormalities. The results show nettles to be rich in Fe which would be beneficial to individuals who are suffering from
Fe deficiency anemia19. After cooking, L. alatipes and O. tenax, respectively contribute 85% and 93% towards the
RDA for Cu, and 28% and 19% towards the RDA for Zn. These values are much higher than those obtained for
L. peduncularis (42% Cu and 14% Zn) and comparable to those obtained for U. dioica (108% Cu and 14% Zn)10.
The results also show L. alatipes and O. tenax, respectively to contribute 38% and 42% towards the DV for Cu, and
20% and 14% towards the DV for Zn, after cooking. This shows the nettles, L. alatipes and O. tenax, to be richer
in essential elements compared to L. peduncularis and U. dioica.
The results of this study show that, while nettles contribute to the dietary reference intakes (DRIs) for essential
elements for most individuals, this contribution is reduced on cooking due to leaching of elements into the cooking water. However, nettles were found to be nutritious, whether cooked or uncooked, with cooking being more
beneficial due to reduction of toxic metal levels.
The results in Table 2 show the concentrations of macronutrients in the different nettles and their contribution
to the RDA and DV for these nutrients. After cooking, L. alatipes and O. tenax, respectively contribute more to
the RDA of proteins (5% and 6%), vitamin C (29% and 31%) and vitamin E (153% and 140%) compared to L.
peduncularis and U. dioica10. A similar trend was observed for DVs. This study shows L. alatipes and O. tenax to
have higher macronutrient content compared to L. peduncularis and U. dioica, after cooking.
Vitamin A deficiency has been shown to be a major nutrient deficiency in South Africa and has been linked
to non-communicable diseases such as xerophthalmia, which is associated with dry eyes and night blindness.
Vitamin C, an effective antioxidant, is a cofactor in numerous physiological reactions such as collagen gene
expression, peptide hormone activation, and carnitine synthesis. Vitamin E is known for its antioxidant activity
especially the inhibition of membrane lipid peroxidation21.
Of the three vitamins determined, only vitamin C was unaffected by cooking in all four nettles. A study conducted on the effect of cooking on vitamin C content of some selected vegetables showed highest loss of vitamin
C in pepper (64.7%) after 30 minutes and lowest loss of vitamin C in spinach (9.9%) after 5 minutes22. Vitamin C,
a water-soluble and heat labile substance will easily leach into water and then degrade by heat. Elevated temperatures and long cooking times have been found to cause loss of vitamin C23. In this study, there was high retention
of vitamin C after 15 minutes of cooking. This could be due to shorter cooking times and low temperatures, which
could have been inadequate for release of vitamin C from its intracellular locations.
Green leafy vegetables have higher retention of vitamin A than root vegetables, which may be attributed to its
increased extractability following denaturation of proteins and a complete breakdown of the cell wall in plants
which occur as a result of cooking22. In this study, there was lower retention of vitamin A and E after cooking of
O. tenax and L. alatipes. Vitamin A is found in the photosynthetic pigment-protein complexes of chloroplasts in
leafy green vegetables, which inhibit its extractability24. Green leafy vegetables have vitamin E occurring mainly
as α-tocopherol which is situated inside chloroplasts25. Cooking could increase extractability by softening plant
walls and disrupting protein complexes. Solubilization of vitamins A and E in cellular lipid emulsions formed
during cooking could decrease retention by the leaves and lead to lower concentrations.
Antioxidant and antidiabetic activities. An antioxidant is a biochemical substance that protects living
cells from damage caused by free radicals that can cause cancer, cardiovascular diseases and other age-related
diseases. The 2,2-diphenyl-l-picrylhydrazyl (DPPH) assay is based on the measurement of the ability of
antioxidants to scavenge the DPPH radical in solution as observed by a loss of color from deep violet to yellow26. In this study, the methanol (MeOH) and dichloromethane (DCM) extracts, and isolated compounds,
β-carotene and β-sitosterol from the nettles, L. alatipes and O. tenax, was evaluated for antioxidant activity. The
extracts showed moderate inhibition of the DPPH radical relative to the known standards, ascorbic acid and
α-tocopherol (Fig. 1a). This was also observed in a previous study on the antioxidant activity of the ethanol
and hot water extracts of Laportea interrupta27. The highest antioxidant activity was exhibited by β-carotene
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Figure 1. (a) DPPH radical scavenging activity and (b) Ferric reducing power of L. alatipes (LA), O. tenax (OT)
and isolated compounds. Values represented as mean ± SD, n = 3. One way Anova and Dunnetts post hoc test
shows significant difference from positive control, ascorbic acid, a) (**p < 0.01 and ***p < 0.001), b) (ns-not
significant, *p < 0.05 and **p < 0.01).
(IC50 = 339 µg mL−1) when compared to the extracts and β-sitosterol, which was comparable to ascorbic acid
(IC50 = 271 µg mL−1).
The ferric reducing antioxidant power (FRAP) assay, which is within the technological reach of most laboratories, evaluates the reduction of Fe3+ to Fe2+ by the donation of an electron by the antioxidant, and it offers
an accepted index of potential antioxidants28. In this study, there was a positive relationship between the concentrations of the plant extracts and the compound with absorbance (Fig. 1b). The MeOH extract of O. tenax
had the highest reducing ability compared to the other extracts however; this was lower than ascorbic acid
and α-tocopherol. Moderate antioxidant activity was observed for the other extracts. Unlike the DPPH assay,
β-sitosterol showed higher reducing ability than β-carotene.
The enzyme responsible for the digestion of dietary carbohydrates in the digestive tract of humans is
α-amylase by acting upon the linkage between the glucose units of carbohydrates. α-Amylase hydrolyzes the
carbohydrates to disaccharides then to glucose. Inhibition of this enzyme slows down the rate of digestion of
carbohydrates, glucose absorption and thereby lowers blood glucose levels, consequently, reducing the postprandial increase of plasma glucose29. An inhibitor of α-amylase reduces the conversion of carbohydrates to
glucose. The effects of plant extracts and isolated compounds on the inhibition of α-amylase are presented in
Fig. 2a. The results showed the response to be dose-dependent. The MeOH extract (IC50 = 190 µg mL−1) and
DCM extract (IC50 = 645 µg mL−1) of O. tenax were shown to be more active than the reference standard, acarbose
(IC50 = 875 µg mL−1). The results suggest that extracts from nettles possess constituents that are able to block the
hydrolysis of 1,4 glycosidic linkage of starch into glucose30. β-sitosterol (IC50 = 1009 µg mL−1) had a lower IC50
value compared to β-carotene (IC50 = 1303 µg mL−1). These two compounds were found in O. tenax indicating
synergistic effects for antidiabetic activity. Extracts of L. alatipes showed inhibition of α-amylase but this was
lower than acarbose.
The inhibition of α-glucosidase activity of the extracts and compounds from nettles is presented in Fig. 2b.
This enzyme is located in the small intestines, catalyzes the digestion and absorption of glucose into the intestines. Inhibition of α-glucosidase decreases the digestion of carbohydrates, thereby decreasing postprandial blood
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Figure 2. (a) Alpha amylase and (b) Alpha glucosidase inhibitory activity of L. alatipes (LA), O. tenax (OT)
and isolated compounds. Values represented as mean ± SD, n = 3; One way Anova and Dunnetts post hoc test
shows significant difference from positive control, acarbose (ns- not significant and *p < 0.05).
glucose levels. There was moderate inhibition of α-glucosidase compared to α-amylase by O. tenax. The inhibitory potential of the DCM extract of L. alatipes (IC50 = 42 µg mL−1) was lower than acarbose (IC50 = 154 µg mL−1).
β-Sitosterol (IC50 = 229 µg mL−1) was a more active inhibitor of α-glucosidase compared to β-carotene. Previous
studies on antidiabetic potential of plants from the Urticaceae family have shown promising results; extracts from
Urtica dioica were reported to have antidiabetic effects in male rats with fructose-induced insulin resistance and
aqueous extracts of Laportea ovalifolia were found to have antihyperglycaemic activity on alloxan diabetic rats31,32.
Conclusion
The results showed cooking to reduce the elemental and vitamin concentrations in nettles, which are temperature
and time dependent. This reduction in concentration is significant when considering potential metal toxicities
due to metals such as Cd and Pb. The radical scavenging activity of the nettles was due to the presence of bioactive
molecules in the plant with β-carotene having the highest activity. The FRAP assay indicated synergistic effects as
the MeOH extract of O. tenax exhibited the highest ferric reducing power. The extracts of the leaves of O. tenax
had higher α-amylase inhibitory activity whilst those of L. alatipes had higher α-glucosidase inhibitory activity.
This study underscores the prospective antidiabetic properties of nettles; however, further studies are required to
confirm this biological activity. Overall, our study supports the consumption of nettles for nutritional benefit and
highlights their potential as nutraceuticals.
Received: 10 November 2019; Accepted: 2 June 2020;
Published: xx xx xxxx
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References
1. Rubatzky, V. E. & Yamaguchi, M. Importance of vegetables in human nutrition in World vegetables: Principles, production, and
nutritive values (eds. Rubatzky, V. E. & Yamaguchi, M.) 34–41 (Springer US (1997).
2. Latham, M. Human nutrition in the developing world. (FAO (1997).
3. Puoane, T. et al. Chronic non-communicable diseases in South Africa: Progress and challenges. S. Afr. Health Rev. 2012/2013
115–126 (2012).
4. World Health Organization (WHO). Healthy diet. https://www.who.int/news-room/fact-sheets/detail/healthy-diet (2018).
5. Dasgupta, A. & Klein, K. Fruits, vegetables, and nuts in Antioxidants in food, vitamins and supplements (eds. Dasgupta, A. & Klein,
K.) 209–235 (Elsevier (2014).
6. American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care 27, s5 LP-s10 (2004).
7. IDF (International Diabetes Federation). IDF diabetes atlas. www.diabetesatlas.org (2017).
8. Phillips, R. Wild Food: A complete guide to foragers. (Macmillan (2014).
9. Warren, P. 101 uses of Stinging Nettles. (Wildeye (2006).
10. Mahlangeni, N. T., Moodley, R. & Jonnalagadda, S. B. The distribution of macronutrients, anti-nutrients and essential elements in
nettles, Laportea peduncularis susp. peduncularis (River nettle) and Urtica dioica (Stinging nettle). J. Environ. Sci. Health, Part B.
51, 160–169 (2016).
11. WHO (World Health Organization). International programme on chemical safety: Cadmium. who.int/ipcs/assessment/public_
health/cadmium/en/ (2020).
12. Wani, A., Ara, A. & Usmani, J. Lead toxicity: a review. Interdiscip. Toxicol. 8, 55–64 (2015).
13. FAO (Food and Agriculture Organization) & WHO (World Health Organization). Joint FAO/WHO food standards programme
Codex committee on contaminants in foods. 13–15 www.fao.orgcf05_INFPDF (2011).
14. Institute of Medicine Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. (The National Academies
Press (2011).
15. WHO (World Health Organization). Fruit and vegetables for health: report of the Joint FAO/WHO Workshop on Fruit and
Vegetables for Health, 1–3 September 2004. (WHO (2005).
16. Naude, C. E. Food-based dietary guidelines for South Africa: The “Eat plenty of vegetables and fruit every day. S. Afr. J. Clin. Nutr.
26, 46–56 (2013).
17. WHO (World Health Organization) & FAO (Food and Agriculture Organization). Food energy – methods of analysis and
conversion factors. FAO Food and Nutrition Paper (WHO/FAO (2002).
18. Bruulsema, T., Heffer, P., Welch, R., Moran, K. & Cakmak, I. Fertilizing crops to improve human health: A scientific review fertilizing
crops to improve human health. Food Nutr. Secur. 1, 1–8 (2012).
19. Phatlhane, D. V. et al. The iron status of a healthy South African adult population. Clin. Chim. Acta. 460, 240–245 (2016).
20. Food and Drug Administration. A food labelling guide: Guidance for industry. www.fda.gov/regulatory-information/search-fdaguidance-documents/guidance-industry-food-labeling-guide (2013).
21. Cruz, R. & Casal, S. Validation of a fast and accurate chromatographic method for detailed quantification of vitamin E in green leafy
vegetables. Food Chem. 141, 1175–1180 (2013).
22. Igwemmar, N. C., Kolawole, S. A. & Imran, I. A. Effect of heating on vitamin C content of some selected vegetables. Int. J. Sci.
Technol. Res. 2, 209–212 (2013).
23. Tian, J. et al. Domestic cooking methods affect the phytochemical composition and antioxidant activity of purple-fleshed potatoes.
Food Chem. 197, 1264–1270 (2016).
24. Bernhardt, S. & Schlich, E. Impact of different cooking methods on food quality: retention of lipophilic vitamins in fresh and frozen
vegetables. J. Food Eng. 77, 327–333 (2006).
25. Bramley, P. et al. Review: Vitamin E. J. Sci. Food Agric. 80, 913–938 (2000).
26. Kedare, S. B. & Singh, R. P. Genesis and development of DPPH method of antioxidant assay. J. Food Sci. Technol. 48, 412–422 (2011).
27. Krishna, C. S., Thankarajan, S. & Thangaraj, P. Evaluation of nutraceutical properties of Laportea interrupta (L.) Chew. Food Sci.
Biotechnol. 23, 577–585 (2014).
28. Menon, S., Rajeshkumar, S. & Venkat Kumar, S. A review on biogenic synthesis of gold nanoparticles, characterization, and its
applications. Resour.-Effic. Technol. 3, 516–527 (2017).
29. Afrisham, R., Aberomand, M., Ghaffari, M. A., Siahpoosh, A. & Jamalan, M. Inhibitory effect of Heracleum persicum and Ziziphus
jujuba on activity of alpha-amylase. J. Bot. 2015, 1–8 (2015).
30. Dutta, J. & Kalita, M. C. In vitro hypoglycaemic evaluation of seven culinary plants of north east India against type 2 diabetes. Asian
J. Pharm. Clin. Res. 9, 209–212 (2016).
31. Ahangarpour, A., Mohammadian, M. & Dianat, M. Antidiabetic effect of hydroalcholic Urtica dioica leaf extract in male rats with
fructose-induced insulin resistance. Iran. J. Med. Sci. 37, 181–186 (2012).
32. Momo, N. E. C., Fomekong, G. D. I., Tazoo, D., Etienne, D. & Oben, J. E. Effect of aqueous and methanol/methylene-chloride
extracts of Laportea ovalifolia (Urticaceae) on blood glucose level in rats. Pharmacologyonline. 118, 105–118 (2007).
Acknowledgements
We are grateful to Unathi Bongoza of the instrumental laboratory and Vuyiswa Mzozonyana of the NMR
spectroscopy unit in the Chemistry department (UKZN). We also are grateful to the National Research
Foundation (NRF) for their funding grant numbers (Roshila Moodley 114008, Nomfundo T. Mahlangeni 83791).
Author contributions
Dr. Nomfundo Thobeka Mahlangeni was the principal investigator and lead author writing up the manuscript.
Dr. Roshila Moodley was the supervisor of the project and editor of the manuscript; she is the corresponding
author. Prof. Sreekantha Babu Jonnalagadda was the budget owner and supervisor of the project.
Competing interests
The authors declare no competing interests.
Additional information
Supplementary information is available for this paper at https://doi.org/10.1038/s41598-020-67055-w.
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