Antioxidant potential and α-glucosidase inhibitory activity of onion (Allium cepa L.) peel and bulb extracts

Allium cepa L. is a commonly consumed vegetable that belongs to the Amaryllidaceae family and contains nutrients and antioxidants in ample amounts. In spite of the valuable food applications of onion bulb, its peel and outer fleshy layers are generally regarded as waste and exploration of their nutritional and therapeutic potential is still in progress with a very slow progression rate. The present study was designed with the purpose of doing a comparative analysis of the antioxidant potential of two parts of Allium cepa, i.g., bulb (edible part) and outer fleshy layers and dry peels (inedible part). Moreover, the inhibitory effect of the onion bulb and peel extracts on rat intestinal α-glucosidase and pancreatic α-amylase of porcine was also evaluated. The antioxidant potential of onion peel and bulb extracts were evaluated using 2,2-diphenyl- 1-picryl hydrazyl (DPPH), ferric-reducing antioxidant power assay (FRAP), 2,2’-azino-bis- 3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging assay, H2O2 radical scavenging activity and Fe2+ chelating activity. Total flavonoids and phenolic content of ethanolic extract of onion peel were significantly greater as compared to that of onion bulb. Ethanolic extract of onion peel also presented better antioxidant and free-radical scavenging activity as compared to the ethanolic extract of bulb, while the aqueous extract of bulb presented weakest antioxidative potential. Onion peel extract’s α-glucosidase inhibition potential was also correlated with their phenolic and flavonoid contents. The current findings presented onion peel as a possible source of antioxidative agents and phenolic compounds that might be beneficial against development of various common chronic diseases that might have an association with oxidative stress. Besides, outer dry layers and fleshy peels of onion exhibited higher phenolic content and antioxidant activities, compared to the inner bulb. The information obtained by the present study can be useful in promoting the use of vegetable parts other than the edible mesocarp for several future food applications, rather than these being wasted.

Evaluation of Antimicrobial and Phytochemical Properties of Agro-Waste and their Potential Applications as Bio-Preservatives and Natural Dyes

Around 40% of agro-waste is generated globally every year most of which is not composted due to improper disposal methods, this increases the carbon footprints which in turn causes a great deal of harm to the environment. The aim of this experiment was to evaluate the antimicrobial and phytochemical properties of extracts prepared of lemon peel (Citrus limon), onion peel (Allium cepa) and potato peels (Solanum tuberosum). The project was an attempt to increase sustainability and decrease waste generation by complete utilization of agro-products prior to disposal. The peels were collected from local restaurants and food joints to aid in reduced waste generation. The extracts were prepared using home-based methods; laboratory extraction using Soxhlet apparatus was carried out for lemon peel extract. For the antimicrobial analysis, four organisms were used, two of which were gram positive (Staphylococcus aureus, Bacillus cereus) and two were gram negative (Escherichia coli, Pseudomonas putida). S.aureus was isolated from a poultry source whereas E.coli was isolated from fish drain water. The lemon peel extracts showed a high degree of antimicrobial activity against all the test organisms, whereas the onion peel extracts positively retarded the growth of both the gram-positive test isolates and consecutively, potato peel extracts showed bactericidal effects against E.coli. The extracts were analyzed for presence of phytochemicals namely, tannins, phenols, saponins, flavonoids, vitamin C; promising results were obtained proving the importance and medicinal relevance of the extracts. To check for preservative attributes of the extracts, quantitative and qualitative examinations were conducted, wherein, efficacious results were noted for the lemon peel extracts, however, actions of onion peel extracts and a combination of extracts was culminated to be inconclusive due to excess coloration/ pigmentation. Lastly textile/ fabric dyes were yielded from the prepared extracts, and as observed, the color was retained by the cloth after addition of mordants.

Potential in Bioethanol Production from Various Agro Wastes Fermenting by Microorganisms Using Carrot Peel, Onion Peel, Potato Peel and Sugar Beet Peel as Substrates

Large amount of agro wastes is produced in Rwanda each year. The global annual potential bioethanol production from the major vegetables wastes such as carrot peel, onion peel, potato peel and sugar beet peel were estimated. Those wastes processing was successfully used as raw materials for the production of bioethanol, employing by cellulase produced from various filamentous fungi including Cladosporium cladosporioides was used for hydrolysis and the fermentation of the hydrolyzed samples was done using Saccharomyces cerevisiae. The fermented product was purified by primary distillation process at 79°C and the fraction was collected. The ethanol is then determined by specific dichromate method and Gas Chromatography. Instantaneous saccharification and fermentation process yielded maximum ethanol in the substrate of carrot peel was 16.9% at 21st day and further confirmed by Gas chromatography and the yield of ethanol obtained was 15.8%.