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. 2022 Mar 31;11(7):950.
doi: 10.3390/plants11070950.

Variations in Total Phenolic, Total Flavonoid Contents, and Free Radicals' Scavenging Potential of Onion Varieties Planted under Diverse Environmental Conditions

Nusrat Bibi  1 , Munir H Shah  2 , Nadeem Khan  3 , Abdulrahman Al-Hashimi  4 , Mohamed Soliman Elshikh  4 , Akhtar Iqbal  1 , Shakeel Ahmad  5 , Arshad Mehmood Abbasi  1
Affiliations

Variations in Total Phenolic, Total Flavonoid Contents, and Free Radicals' Scavenging Potential of Onion Varieties Planted under Diverse Environmental Conditions

Nusrat Bibi et al. Plants (Basel). .

Abstract

Genetic diversity and Agro-climatic conditions contribute significantly to the agronomic and morphological features of the food plant species, and their nutraceutical potential. The present study was intended to evaluate the impact of growing conditions on total phenolic and total flavonoid contents, and in vitro antioxidant potential in the bulbs and leaves of onion varieties planted under diverse environmental conditions. Standard analytical methods were used to quantify total phenolic content (TPC), total flavonoid content (TFC), and free radicals’ scavenging/antioxidant capacity. The impact of climatic and soil conditions was assessed using statistical tools. In general, onion varieties cultivated at three different locations viz. Kalar Kahar, Lahore and Swabi exhibited significant variations in TPC and TFC, and antioxidant activities. The bulbs and leaves of Mustang (V1) variety planted at Lahore and Swabi had significantly (p < 0.05), high levels of TPC (659.5 ± 6.59, and 631.1 ± 8.58 mg GAE/100 g, respectively). However, leaves of Red Orb (V2) and bulbs of Mustang (V1), and Golden Orb (V6), harvested from Kalar Kahar depicted the highest concentration of TFC (432.5 ± 10.3, 303.0 ± 6.67, and 303.0 ± 2.52 mg QE/100 g DW, respectively). Likewise, bulbs of V1 planted at Kalar Kahar, Lahore and Swabi exhibited maximum inhibition of DPPH, ABTS, and H2O2 radicals (79.01 ± 1.49, 65.38 ± 0.99, and 59.76 ± 0.90%, respectively). Golden Orb (V6) harvested from Lahore had the highest scavenging of OH radical (67.40 ± 0.09%). Likewise, bulbs of V1 variety planted at KalarKahar and Swabi had significant capacity to scavenge ferric ions (415.1 ± 10.6 mg GAE/100 g DW), and molybdate ions (213.7 ± 0.00 mg AAE/100 g DW). Conversely, leaves of Amazon (V8), planted at Lahore and Swabi depicted significant levels of DPPH, ABTS, H2O2 radical scavenging (90.69 ± 0.26, 63.55 ± 1.06, 51.86 ± 0.43%, respectively), and reduction of ferric ions (184.2 ± 6.75 mg GAE/100 g DW). V6 leaves harvested from Lahore and that of Super Sarhad (V3) from Swabi showed the highest inhibition of OH radical (61.21 ± 0.79%), and molybdate ions (623.6 ± 0.12 mg AAE/100 g DW), respectively. Pearson correlation and principal component analysis revealed strong relationships of climatic conditions, soil properties and elevation with TPC, TFC and free radicals’ scavenging potential in the bulbs and leaves of onion varieties. The variations in the total phenolic and flavonoid contents, and antioxidant potential of different varieties, and their associations with climatic and soil factors revealed the complexity of the growing conditions and genetic makeup that imposed significant impacts on the synthesis of secondary metabolites and nutraceutical potential of food and medicinal plant species.

Keywords: antioxidant activity; climate; environment; flavonoid; onion; phenolic; soil.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Snapshots of onion varieties. Mustang (V1), Red Orb (V2), Super Sarhad (V3), Red Flame (V4), Pulkara (V5), Golden Orb (V6), White Pearl (V7), Amazon (V8), Zeus (V9).
Figure 2
Figure 2
Location map showing plantation sites of onion varieties.
Figure 3
Figure 3
Plantation of onion varieties in the study areas.
Figure 4
Figure 4
Comparative assessment of TPC and TFC in the bulbs and leaves of onion varieties at different plantation sites. Different letters (a–c/A–C), indicate significant differences (p < 0.05) in TPC and TFC.
Figure 5
Figure 5
Comparative assessment of DPPH and OH radicals’ scavenging in the bulbs and leaves of onion varieties at different plantation sites. Different letters (a–c/A–C) indicate significant difference (at p < 0.05) in bulbs and leaves at different locations.
Figure 6
Figure 6
Comparative assessment of H2O2 and ABTS radicals scavenging in the bulbs and leaves of onion varieties at different plantation sites. Different letters (a–c) indicate significant difference between values at p < 0.05. Different letters (a–c/A–C) indicate significant difference (at p < 0.05) in bulbs and leaves at different locations.
Figure 7
Figure 7
Comparative assessment of FRAP and PMA values in the bulbs and leaves of onion varieties at different plantation sites. Different letters (a–c/A–C) indicate significant difference (at p < 0.05) in bulbs and leaves at different locations.
Figure 8
Figure 8
Principal component matrices for climatic and soil factors at planted sites of onion varieties.
Figure 9
Figure 9
Principal component analysis TPC, TFC and antioxidant properties in bulbs (A) and leaves (B) of onion varieties planted at diverse locations.
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