Jimmy Sumani

This study investigated the chemical composition, antioxidant, and antibacterial activities of two medicinal plants from Malawi: Zanthoxylum chalybeum and Euphorbia ingens. Plant extracts were obtained sequentially macerating the root powder with n-hexane, dichloromethane, ethyl acetate, methanol, and water. Total phenolics and flavonoids were determined by the Folin-Ciocalteau and aluminum chloride methods, respectively, while antioxidant activity was assessed by DPPH and FRAP assays. The antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa was evaluated using the disc diffusion method. Flavonoids ranged from 13.40 to 30.27 mg/g for Z. chalybeum extracts and 21.76 to 66.27 mg/g for E. ingens, with the highest amounts in ethyl acetate extracts of both plants. Both plants had the highest amounts of total phenolics in methanol extracts, with Z. chalybeum and E. ingens exhibiting 284.85 and 351.59 mg/g, respectively. The DPPH radical scavenging activity test showed that E. ingens, with IC50 values of 11.28 and 12.85 ?g/mL for the aqueous and methanol extracts, respectively, is a stronger antioxidant than Z. chalybeum. The FRAP activity was highest in methanol extracts for E. ingens (2831.77±179.02 mg/g) and Z. chalybeum (799.15±32.43 mg/g). Both plants exhibited more potent antibacterial activity against S. aureus compared to P. aeruginosa. Dichloromethane and ethyl acetate extracts of Z. chalybeum showed significant activity against S. aureus with MIC values of 1.56 mg/mL, demonstrating their strong inhibitory potential. The study has revealed that both E. ingens and Z. chalybeum roots would be excellent natural antioxidants and antibacterial agents.

Consumers’ preference on the food market has shifted from food safeguarded with artificial preservatives to that safeguarded with antimicrobial and antioxidant preservatives derived from natural sources. This is why there is a growing interest among researchers in the food and beverage industry to explore natural antimicrobial and antioxidant preservatives as an alternative to artificial preservatives. The present investigation is, therefore, aimed at synthesising the current outcomes that have achieved success in safeguarding spoilage and growth of spoilage microbes on foodstuffs. The present study used a literature review–based approach in which peer‐reviewed published papers on ‘antimicrobials and antioxidants from agri‐food wastes’ were accessed from ScienceDirect, PubMed, Google Scholar, PLOS, SciFinder and Web of Science databases. The findings from the papers on the antimicrobial and antioxidant activities of different agrifood wastes such as Citrus limon peel, Allium cepa peel, Malus domestica seeds, Daucus carota peels, Beta vulgaris peel, citrus fruit peel, Musa acuminate peels and Vitis vinifera waste extracts on meat, milk and baked products were systematically reviewed. The literature revealed that natural antioxidants resulted in a reduction in the oxidative processes in tested meat, milk and baked products. Similarly, the natural antimicrobials resulted in inhibition of the spoilage microbe growth, thereby extending the shelf life of various foods. The antioxidant and antimicrobial activities of the agrifood waste extracts were attributed to the existence of phytochemical compounds such as phenolic acids, gallic acid, vanillic acid and flavonols. The literature has shown that bioactive compounds in agrifood waste are suitable natural antimicrobials and antioxidants and demonstrated the increase in the shelf life of food products.

Terrestrial orchid tubers are an important source of food in some parts of Africa and are traditionally included in the diets of most rural communities in Malawi. However, there is limited information on the nutritional and phytochemical content of the Malawian orchids to substantiate their traditional use. The present study evaluates the nutritional and phytochemical variation of four orchid species: Disa zombica, Satyrium buchananii, Satyrium carsonii, and Satyrium trinerve, collected from the same ecological zone of Malawi. The proximate content, minerals, phytochemicals, and functional properties were analysed using official procedures. Protein ranged from 2.19% to 4.65%, whereas carbohydrate ranged from 65.24% to 80.22%, with S. carsonii and S. trinerve registering the highest protein and carbohydrate contents, respectively. Iron and potassium were highest in D. zombica, while sodium and calcium were highest in S. buchananii. The total phenolics ranged from 228.56 to 500.00 mg GAE/100 g, with D. zombica registering the highest. The water absorption capacity ranged from 4.10 to 10.88 g/g. Despite variable levels, the study provides evidence that orchid species contain essential nutrients and phytochemicals important for human nutrition and health. Furthermore, the functional properties can be utilised in the development of food products, such as baked products.

Terrestrial orchid tubers are an important source of food in some parts of Africa and are traditionally included in the diets of most rural communities in Malawi. However, there is limited information on the nutritional and phytochemical content of the Malawian orchids to substantiate their traditional use. The present study evaluates the nutritional and phytochemical variation of four orchid species: Disa zombica, Satyrium buchananii, Satyrium carsonii, and Satyrium trinerve, collected from the same ecological zone of Malawi. The proximate content, minerals, phytochemicals, and functional properties were analysed using official procedures. Protein ranged from 2.19% to 4.65%, whereas carbohydrate ranged from 65.24% to 80.22%, with S. carsonii and S. trinerve registering the highest protein and carbohydrate contents, respectively. Iron and potassium were highest in D. zombica, while sodium and calcium were highest in S. buchananii. The total phenolics ranged from 228.56 to 500.00 mg GAE/100 g, with D. zombica registering the highest. The water absorption capacity ranged from 4.10 to 10.88 g/g. Albeit variable levels, the study provides evidence that orchid species contain essential nutrients and phytochemicals important for human nutrition and health. Furthermore, the functional properties can be utilised in the development of food products, such as baked products.

Vernonia glabra is used by Malawian traditional healers to treat a myriad of ailments including shingles, diabetes, dysentery, diarrhoea, cough, wounds, gonorrhoea, and gastrointestinal problems. This study evaluated phytoconstituents and the in vitro antimycobacterial activities of the crude extracts and fractions from roots of Vernonia glabra. Agar disk diffusion and modified broth microdilution assays were used to determine the antimycobacterial activities of dichloromethane (DCM) and ethyl acetate (EtOAc) crude extracts and fractions from the roots. Gas chromatography-mass spectrometry (GC-MS) and Fourier-transform infrared spectroscopy (FTIR) analyses were used to characterise the major compounds in the crude extracts and fractions. The EtOAc fraction exhibited the highest antimycobacterial activity against Mycobacterium tuberculosis H37Rv. The EtOAc fraction achieved a minimum inhibitory concentration (MIC) of 4.88μg/mL and a half-maximal inhibitory concentration (IC₅₀) value of 38.37μg/mL, whereas gentamycin, a standard drug, achieved MIC and IC₅₀ values of 3.13μg/mL and 3.88μg/mL, respectively. GC-MS and FTIR analyses of the EtOAc fractions revealed the presence of hexadecenoic acid, methyl ester (0.39), diisooctyl phthalate (24.56), oxalic acid, allyl undecyl ester (4.66), bis(2-ethylhexylphthalate) (5.41), octacosane (51.12), tetradecane (12.63), phenol, 3,5-bis(1,1-dimethylethyl) (0.07), and 2-hydroxy-4-methylbenzaldehyde (6.47). The identified compounds are reported in the literature to possess antimicrobial and anticancer activities. It was evident from the comparison of the hill slope (HS) values of the dose-response curves of the fraction (1.005) and its crude extract (1.322) that repeated fractionation improved the activity. Therefore, this study showed that the roots of Vernonia glabra present a potential source of new leads for antimycobacterial drugs.