Phytochemical contents, antioxidant activity and functional properties of Raphanus sativus L, Eruca sativa L. and Hibiscus sabdariffa L. growing in Ethiopia

Antioxidant Potential of Ethiopian Medicinal Plants and Their Phytochemicals: A Review of Pharmacological Evaluation

Background

Free radicals are very reactive molecules produced during oxidation events that in turn initiate a chain reaction resulting in cellular damage. Many degenerative diseases in humans, including cancer and central nervous system damage, are caused by free radicals. Scientific evidence indicates that active compounds from natural products can protect cells from free radical damage. As a result, the aim of this review is to provide evidence of the use of diverse Ethiopian medicinal plants with antioxidant properties that have been scientifically validated in order to draw attention and foster further investigations in this area.

Methods

The keywords antioxidant, radical scavenging activities, reactive oxygen species, natural product, Ethiopian Medicinal plants, and 2, 2-Diphenyl-1-picrylhydrazyl radical scavenging assay (DPPH) were used to identify relevant data in the major electronic scientific databases, including Google Scholar, ScienceDirect, PubMed, Medline, and Science domain. All articles with descriptions that were accessed until November 2022 were included in the search strategy.

Results

A total of 54 plant species from 33 families were identified, along with 46 compounds isolated. More scientific studies have been conducted on plant species from the Brassicaceae (19%), Asphodelaceae (12%), and Asteraceae (12%) families. The most used solvent and extraction method for plant samples are methanol (68%) and maceration (88%). The most examined plant parts were the leaves (42%). Plant extracts (56%) as well as isolated compounds (61%) exhibited significant antioxidant potential. The most effective plant extracts from Ethiopian flora were Bersama abyssinica, Solanecio gigas, Echinops kebericho, Verbascum sinaiticum, Apium leptophyllum, and Crinum abyssinicum. The best oxidative phytochemicals were Rutin (7), Flavan-3-ol-7-O-glucoside (8), Myricitrin (13), Myricetin-3-O-arabinopyranoside (14), 7-O-Methylaloeresin A (15), 3-Hydroxyisoagatholactone (17), β-Sitosterol-3-O-β-D-glucoside (22), Microdontin A/B (24), and Caffeic acid (39).

Conclusion

Many crude extracts and compounds exhibited significant antioxidant activity, making them excellent candidates for the development of novel drugs. However, there is a paucity of research into the mechanisms of action as well as clinical evidence supporting some of these isolated compounds. To fully authenticate and then commercialize, further investigation and systematic analysis of these antioxidant-rich species are required.

Antioxidant Capacity of Polar and Non-Polar Extracts of Four African Green Leafy Vegetables and Correlation with Polyphenol and Carotenoid Contents

In sub-Saharan Africa, chronic malnutrition is often associated with intestinal inflammation and oxidative stress. African green leafy vegetables (GLVs), commonly consumed by these populations and rich in bioactive compounds, may improve the antioxidant status. The aim of this study was to measure the antioxidant capacity using complementary assays (DPPH, FRAP, ABTS, ORAC and NO scavenging) in polar and non-polar leaf extracts of four African GLVs, cassava (Manihot esculenta), roselle (Hibiscus sabdariffa), jute mallow (Corchorus olitorius), and amaranth (Amaranthus spp.), with spinach (Spinacia oleracea) chosen as a reference. Their antioxidant capacity was correlated with their total polyphenol (TPC), flavonoid (TFC), condensed tannin, lutein, and β-carotene contents. Identification of phenolic compounds by UHPLC-DAD-MS/MS revealed the presence of three main classes of compound: flavonols, flavones, and hydroxycinnamic acids. Cassava and roselle leaves presented significantly higher TPC and TFC than amaranth, jute mallow, and spinach. They also exhibited the highest antioxidant capacity, even higher than that of spinach, which is known for its important antioxidant effect. The antioxidant capacity was 2 to 18 times higher in polar than non-polar extracts, and was more strongly correlated with TPC and TFC (R > 0.8) than with β-carotene and lutein contents. These findings provide new data especially for cassava and roselle leaves, for which studies are scarce, suggesting an appreciable antioxidant capacity compared with other leafy vegetables.

Proximate composition and selected phytochemical component of Dawrach (Raphanus raphanistrum L.) as affected by blanching temperature

Dawrach (Raphanus raphanistrum L.) is an underutilized wild edible plant belonging to the Brassicaceae family. Dawrach is widely regarded as a weed, and there is a lack of information about its nutritional profile such as, proximate, antioxidant properties, health-promoting vitamins, minerals and significant phytochemicals. The plant also contains anti-nutrients which need a pretreatment to be minimized and deteriorating enzymes that should be inactivated to make shelf stable products. Blanching temperature is the most critical factor that needs great attention during the blanching process to minimize the anti-nutrients and minimize the loss of desirable components of Dawrach such as, proximate and phytochemical contents and antioxidant activity. Thus, this study aimed to investigate the influence of blanching temperatures on the proximate, phytochemicals and antioxidant activity of Dawrach leaves. The parameters were evaluated following standard analytical methods and procedures. Dawrach leaves were blanched at 50, 60, 70, 80, and 90 °C temperature for 3 min, and raw or unblanched Dawrach was used as a control. Blanching temperature significantly affected the proximate, phytochemicals, antioxidant activity and anti-nutrients of the Dawrach. As a result, the moisture content of raw and blanched at 90 °C was 10.77 and 7.69 g/100g, respectively. Thus, blanching decreases the moisture content of Dawrach to the recommended safe moisture level for the products. Moreover, there was a significant decrease in the values of antioxidants activities, beta carotene, and l-ascorbic acid as the blanching temperature increased from 50 to 90 °C. Besides, as blanching temperature increased, there was a reduction in oxalate and tannin of the Dawrach leaf.

Phytochemical profile and antioxidant capacity of some wild edible plants consumed in Southwest Ethiopia

Wild edible plants (WEPs) such as Solanum nigrum L., Vigna membranacea A. Rich., Dioscorea praehensilis Benth., Trilepisium madagascariense DC., and Cleome gynandra L. are widely used for various forms of culinary and folk medicine in Southwest Ethiopia. However, the phytochemical content of these plants is not explored. Thus, this study aimed to determine the total phenols, flavonoids, antioxidants, vitamin C, and β-carotene in edible parts of the plants. Edible parts were oven-dried and extracted with methanol. Total phenolic content (TPC) and total flavonoid content (TFC) were determined using Folin Ciocalteu and Aluminium chloride colorimetric methods, respectively. In vitro, antioxidant activities were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) tests. β-carotene and vitamin C content were assessed using spectrophotometric and titration, respectively. TPC ranged from 0.25 ± 0.06 mg GAE/g in D. praehensilis tuber to 35.73 ± 2.52 mg GAE/g in S. nigrum leaf, while TFC varied from 0.85 ± 0.03 to 11.25 ± 0.01 mg CE/g in D. praehensilis tuber and C. gynandra leaf. In the DPPH assay, the antioxidant value ranged from 50.09% in D. praehensilis tuber to 87.63% in S. nigrum leaf; while in the FRAP assay, the value ranged from 49.16 ± 2.13 in D. praehensilis tuber to 188.12 ± 1.13 mM Fe²⁺/100 g in S. nigrum leaf. Similarly, β-carotene content was recorded between 11.81 ± 0.00 mg/100g in D. praehensilis tuber to 34.49 ± 0.95 mg/100g in V. membranacea leaf. The concentration of vitamin C ranged from 10.00 ± 0.61 in D. praehensilis tuber to 45 ± 1.80 mg/100g in V. membranacea leaf. The results showed strong positive correlations between FRAP and TPC (r = 0.94), and FRAP and vitamin C (r = 0.93). S. nigrum and C. gynandra contain abundant levels of TPC and TFC. V.membranacea leaf contains a good source of vitamin C and β-carotene. These WEPs contribute a natural supply of dietary antioxidants that prevent oxidative stress.

Nutritional Composition, Antinutrient Contents, and Polyphenol Compounds of Selected Underutilized and Some Commonly Consumed Vegetables in East Wollega, West Ethiopia

In Ethiopia, some plants (Ethiopia kale, Swiss chard, and celery) remain underutilized for human consumption, as information on their nutritional potential remains limited. As a result, the purpose of this study was to determine the proximate, mineral, antinutrient, and phytochemical content of Ethiopia kale (Brassica carinata), Swiss chard (Beta vulgaris), carrot (Daucus carota), tomato (Lycopersicon esculentum), and cabbage (Brassica oleracea) using standard analytical methods. The moisture, crude protein, crude fiber, crude fat, total ash, total carbohydrate, and energy contents were found to be 6.44–16.62%, 6.76–33.64%, 9.19–54.86%, 0.50–4.00%, 1.00–2.75%, 7.28–68.73%, and 141.06–333.28 kcal/100 g, respectively. Ethiopia's kale had a high protein content, while celery had a high fat and fiber content. The calcium, magnesium, iron, phosphorous, potassium, zinc, and sodium content (mg/100 gdb) ranged between 8.00 and 306.00, 8.10–11.83, 0.64–4.85, 11.34–63.00, 2.83–810.00, 0.15–41.65, and 1.50–443.80 mg/100 g, respectively. Swiss chard contained magnesium, potassium, and sodium, whereas celery was high in calcium and iron. The total oxalate, condensed tannin, and phytate (mg/100 gdb) ranged as follows: 0.88–4.92, 138.27–892.19, and 69.14–265.99, respectively. Ethiopia’s kale recorded a comparatively low amount of tannin and phytate. High mineral bioavailability, such as calcium, iron, and zinc, was obtained in Ethiopia kale. The results also showed that Ethiopia's kale contained a good amount of total phenolic and flavonoid content. The findings indicated that Ethiopia kale was a significant source of protein, had low antinutrient content with high mineral bioavailability, and had the potential to formulate nutrient-rich infant and young child foods using staple cereals and pulse grains.

Effect of Plasma Activated Water on Selected Chemical Compounds of Rocket-Salad (Eruca sativa Mill.) Leaves

Plasma activated water (PAW) has proven to be a promising alternative for the decontamination of rocket leaves. The impact of PAW on the volatile profile, phytosterols, and pigment content of rocket leaves was studied. Leaves were treated by PAW at different times (2, 5, 10, and 20 min). Compounds of the headspace were detected and quantified using GC–MS analysis. A total of 52 volatile organic compounds of different chemical classes were identified. Glucosinolate hydrolysis products are the major chemical class. PAW application induced some chemical modifications in the volatile compounds. Changes in the content of the major compounds varied with the increase or decrease in the treatment time. However, PAW-10 and -2 were grouped closely to the control. A significant decrease in the content of β-sitosterol and campesterol was observed after PAW treatment, except for PAW-10, which showed a non-significant reduction in both compounds. A significant increase in β carotene, luteolin, and chlorophyll b was observed after the shortest treatment time of PAW-2. A reduction in chlorophyll content was also observed, which is significant only at longer treatment, or PAW-20. Overall, PAW has proven to be a safe alternative for rocket decontamination.

Anti-Multiple Myeloma Potential of Secondary Metabolites from Hibiscus sabdariffa-Part 2

Multiple Myeloma (MM) is an aggressive tumor causing millions of deaths every year and currently available therapies are often unsuccessful or correlated with severe side effects. In our previous work we demonstrated that the Hibiscus sabdariffa hydroalcoholic extract inhibits the growth of the MM cell line and we isolated two metabolites responsible for the activity: Hib-ester and Hib-carbaldehyde. Herein we report their interaction with proteasome, one of the main targets in the fight against MM. The molecular modelling study outlined a good interaction of both compounds with the target and these results prompted us to investigate their potential to inhibit proteasome. Metabolites were then isolated from the calyces and an extract with a high content of Hib-ester and Hib-carbaldehyde was prepared. An anticancer profile was drawn, evaluating apoptosis, autophagy and proteasome inhibition, with the anticancer properties being mainly attributed to the Hib-ester and Hib-carbaldehyde, while the proteasome inhibition of the extract could also be ascribed to the presence of anthocyanins, a class of secondary metabolites already known for their proteasome inhibitory activity.

Optimization of nutritional and sensory qualities of complementary foods prepared from sorghum, soybean, karkade and premix in Benishangul - Gumuz region, Ethiopia

Consumption of nutritionally deficient complementary foods in developing countries is among the main contributing factors to infants and young children's malnutrition. Therefore, this study was aimed to optimize the nutritional and sensory properties of complementary food made from malted sorghum, blanched soybean, boiled karkade seeds and premix. A D-optimal mixture experimental design with 18 runs was generated by design expert software within in the constrained: 40-60% malted sorghum, 20-30% blanched soybean, 10-20% boiled karkade seeds and 10% premix (5.0% figl leaf powder, 4.5% sugar and 0.5% iodized table salt). Statistical model evaluation and optimization were done using D-optimal mixture design expert software. Sensory evaluation was conducted using 53 untrained panelists on two selected formulations and the control (local formulation). The study shows that with an increasing ratio of blanched soybean and boiled karkade seeds flour in the blend, a significant (p < 0.05) increase in protein, fat, energy and mineral contents, and a decrease in tannin and phytic acid contents of high mineral bioavailability except for oxalate: calcium ratio in the formulations were observed. The optimal blending ratio was 45.0% malted sorghum, 26.0% blanched soybean, and 19.0% boiled karkade seeds flour plus 10.0% premix. The gruel made from the new formula was significantly (p < 0.05) liked in terms of aroma, flavor, mouthfeel and overall acceptability than the control sample. The findings suggested that the optimal mix of these traditionally processed ingredients can potentially alleviate protein-energy malnutrition and micronutrient deficiency to mitigate expensive commercial infant complementary foods sold in the market.