Abstract
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.
Highlights
Humans have been using naturally occurring indigenous plants including herbs, fruits and vegetables as therapies to various illnesses, But, over the course of time, the progress in advanced and effective technology along with development of synthetic drugs has prominently lowered the demand and popularity of the natural medicine approach
Plants and herb-based extracts are regarded as better sources of functional nutrients that can aid in the prevention and management of certain non-communicable diseases (NCDs)
Several researches conducted on plants and herbs which contain phenolics in abundant quantities have reported a link between antioxidant activity of extract and inhibition of α-glucosidase activity (Kwon et al, 2006) and Allium cepa bulb have been evaluated for it’s several physiological effects including anti-diabetic properties (Wu and Xu, 2011)
Summary
Humans have been using naturally occurring indigenous plants including herbs, fruits and vegetables as therapies to various illnesses, But, over the course of time, the progress in advanced and effective technology along with development of synthetic drugs has prominently lowered the demand and popularity of the natural medicine approach. Allium cepa (onion) has got great economic importance throughout the world as it is a common dietary item in most populations and is believed to be among the initially grown crops of world probably due to its greater shelf life and portability It has been evaluated as a supple source of sulphur containing compounds, variety of flavonoids, and dietary fiber (Takahashi and Shibamoto, 2008). Like inside the gastrointestinal tract the absorption of dietary disaccharides like sucrose and maltose via intestine is done with the help of a group of α- glucosidases like intestinal sucrase, isomaltase, maltase and glucoamylase When activities of these enzymes are inhibited it brings prominent reduction in the level of blood glucose after the consumption of carbohydrate rich meal and can play a key role in the management of diabetes and its associated complications (Lamine et al, 2019). In current research we assessed and compared the antioxidant and enzyme inhibiting potential of onion peel and bulb extracts to find new potential sources of natural antioxidants and investigated the potential relationship between antioxidant activity and α-glucosidases/α-amylase inhibitory activity
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