Studies on biochemical and nutraceutical profiling of 43 Indian onion (Allium cepa L.) genotypes

The onion bulb is packed with a variety of phytochemicals that offer health benefits. Indian onions, in particular, are recognized for their strong flavor and taste. This study focuses on analyzing the nutraceutical profile of 43 Indian onion varieties. It examines several key components, including pyruvic acid (PA), total sugars (TS), reducing sugars (RS), non-reducing sugars (NRS), total flavonoids (TF), total phenols (TP), antioxidant activity (AOA), moisture content (MC), and total soluble solids (TSS). Significant differences were observed across the genotypes for these biochemical components. Pyruvic acid content ranged from 0.19 to 9.37 µmol/g fw (fresh weight), with the lowest level recorded in GJRO-11 and the highest in Pusa Riddhi. We also examined the effects of pungency on the composition of these biochemicals. Pungency influenced the levels of fructose, glucose, sucrose, total phenols, and antioxidant activity. While sucrose content was higher in sweet onions, fructose and glucose levels were slightly reduced. The total sugar content among the genotypes ranged from 3.42% in Arka Kalyan to 7.22% in Bhima Shakti. Red onion varieties exhibited higher antioxidant activity, whereas white onions showed significantly lower activity. The total phenol content, estimated using the Folin-Ciocalteu method, ranged from 0.70 mg/g fw in POH-1 to 3.54 mg/g fw in N-2-4-1. Total flavonoid content varied from 1.13 mg/g fw in GWO-1 to 2.28 mg/g fw in Phule Safed. Antioxidant activity, measured using the FRAP assay, ranged from 0.41 µmol/g fw in Bhima Shweta to 1.36 µmol/g fw in NHRDF Red. Moisture content ranged from 74.64% in Bhima Raj to 88.52% in Arka Pragati. TSS content ranged from 11.27 in GJWO-3 to 14.40% in Pillipatti Junagadh. We also studied the effect of bulb color on these biochemical compositions. Our results suggest that bulb color significantly impacted the levels of pyruvic acid, reducing sugars, total phenols, antioxidant activity and TSS. Correlation analysis revealed strong positive correlations between reducing sugars and total flavonoids, non-reducing sugars and total sugars, as well as total phenols and antioxidant activity. Principal Component Analysis (PCA) revealed that the first two components explained 54.3% of the cumulative variation, with PC1 primarily contributed by RS, TF, MC and TSS, and PC2 by TS, NRS, and TP. These findings provide valuable insights for the selection and integration of these traits into desirable onion genotypes to enhance overall quality and health benefits.