Outer papery peel of onion bulb is an inevitable bio-waste generated in the course of postharvest handling and processing. Onion peels are rich source of nutraceutically important polyphenolic compounds having many therapeutic potentials. In this study, we characterized onion peel extract (OPE) of eight differentially pigmented short-day onion varieties through ultra-high-performance liquid chromatography coupled with high-resolution single stage Orbitrap spectrometry and evaluated the antioxidant potential. A total of 49 phenolic compounds were identified in this study which include 33 anthocyanin, 8 flavanol, 4 flavones, and 1 each of pyranoanthocyanin, chalcone, phenolic acid, and ellagitannins. Anthocyanin was the most abundant polyphenolic compound followed by flavanol in all the varieties. Among anthocyanin, 10 cyanidin, 10 delphinidin, 4 peonidin, 4 petunidin, 3 pelargonidin, and 2 malvidin were identified. Cyanidin-3-(6-malonylglucoside), delphinidin, and delphinidin-3-galactoside were the predominant pigment in dark red varieties (BDR and BRJ), and its abundance suggests a key role in the differential pigmentation pattern of onion peel. Total phenol content (TPC) in peels ranged from 1738.21 to 1757.76 mg GAE/100 g DW in dark red onion, 1306.58 to 1646.73 mg GAE/100 g DW in red onion, and 78.77 to 85.5 mg GAE/100 g DW in white onion varieties. The mean total anthocyanin content was maximum (28.23 mg/100 g DW) in dark red varieties (BDR) and minimum (0.11 mg/100 g DW) in white variety (BSW). Total antioxidant activity ranged from 4.71 to 79.80 μmol/g DW, 22.71 to 286.7 μmol/g DW, and 8.72 to 156.89 μmol/g DW estimated through FRAP, ABTS, and DPPH methods, respectively. In all three methods, it was maximum in dark red var. BDR and minimum in white var. BSU.

Apart from the culinary usage, Alliums are known for their therapeutic potential since antiquity. Alliums contain diverse bioactive compounds such as, sulfur-containing compounds (allicin, diallyl sulfides), flavonoids, and saponins. These compounds have demonstrated a wide range of pharmacological actions, including antioxidant, anticancer, anti-inflammatory, antimicrobial, neuroprotective, cardioprotective activities and treatment of metabolic disorders such as diabetes and hyperlipidemia. Despite encouraging preclinical results, translating these findings into clinical practice remains difficult, necessitating more rigorous human trials and molecular research. One of the major constrain in enhancing the therapeutic efficacy of these bioactive compound is to develop large-scale extraction techniques besides improving their stability, solubility, and bioavailability. The current scenario urges to focus research on optimizing the bioavailability of these compounds, evaluate their synergistic effects with existing therapies, as well as their long-term safety. This perspective article provides a comprehensive overview of the therapeutic potential of Allium spp. and suggests the key avenues for future research aiming at realising their full clinical potential.

Onion varieties (Bhima Kiran, Bhima Raj, Bhima Red, Bhima Shakti, Bhima Shubra, Bhima Shweta and Bhima Super) were evaluated for storage losses during rabi season of 2013–14 and 2014–15. All the varieties were grown under similar conditions and stored at ambient conditions in a modified bottom and top ventilated storage structure. Total losses were found significantly less in B. Kiran (26.66%) and B. Shakti (35.87%) after four months of storage, whereas no significant difference was observed among these two varieties. In the year 2014–15, the bulbs were analyzed for rate of respiration and total phenol content. No significant difference was observed in rate of respiration at the beginning of storage. Total phenol content was significantly high in B. Raj (186.33 mg GAE/100g) followed by B. Kiran (138.64 mg GAE/100g), B. Shakti (137.09 mg GAE/100g), B. Shweta (114.29 mg GAE/100g) and B. Shubra (112.04 mg GAE/100g). Significantly low phenol content was observed in B. Red (35.16mg GAE/100 g). During storage, rate of respiration and total phenol content increased up to 60 days of storage and then decreased up to 90 days.