Effect of Foliar Application of Selenite On Organic Se and Antioxidant Activity in Kiwifruit

Elevating the selenium concentration in fruit has the potential to enhance the average dietary selenium intake in humans. The application of selenium fertilizer through a spraying method has been found to be an effective approach for producing selenium-enriched fruit. While kiwifruit (Actinidia chinensis) is known for its ability to accumulate selenium, the ‘Hongyang’ variety grown in Sichuan, China has been observed to have low selenium content. The tree was treated by spraying the leaves with water solution containing 10, 25, 50 and 100 mg per litre in the form of sodium selenite (Na₂SeO₃) in the flowering period. The total Se and organic Se content, and the effects of different concentrations of Na₂SeO₃ on antioxidant activity in peels, pulps and seeds of fruits were investigated. The findings indicated that kiwifruit has the ability to transform exogenously absorbed inorganic selenium into organic selenium. The organic selenium content in the pulps treated with 50 mg L⁻¹ sodium selenite was 9.04 times higher than in the control treatment. Furthermore, protein-Se was identified as the main component of organic selenium, comprising 48.04–51.15% of the pulps. The protein-Se is the primary component of organic Se, which the proportion in pulps was 48.04–51.15%. The application of 50 and 100 mg L⁻¹ sodium selenite via foliar spraying resulted in a notable enhancement of ferric reducing/antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) values across all tissues. A significant positive correlation between FRAP value and organic Se content in pulps, and a significant relationship between ORAC values and protein-Se and polysaccharide-Se content of kiwifruit tissue showed regression equation. In general, the optimum Se application is 50 mg L⁻¹, and some areas with a severe selenium deficiency can apply 100 mg L⁻¹ selenite. It might serve as a source of selenium in dietary supplements or as an ingredient for the formulation of nutraceuticals.