Iodine is a trace element whose deficiency impacts human health. Iodine's function is participation in the synthesis of thyroid hormones. It also has therapeutic potential to counteract oxidative stress by increasing antioxidant capacity. Biofortification is one of the most promising methods for enriching plants with this element.

The study aimed to determine the effect of biofortification with mineral (KI) and organic forms of iodine: 5-iodosalicylic acid (5-ISA) and 3,5-diiodosalicylic acid (3,5-diISA) on the antioxidant properties of Eschscholzia californica grown in a hydroponic system. The following combinations were tested: (1) Control; (2) KI; (3) 5-ISA; (4) 3,5-diISA.

For the determination of antioxidant activity, ethanol extracts (80% v/v) of California poppy plants were prepared. These parameters were determined using the DPPH radical, ABTS radical, FRAP, and CUPRAC methods. Absorbance was measured 10 minutes after the addition of solutions at 516, 734, 595, and 450 nm, respectively.

No significant differences were observed using the DPPH, ABTS, or CUPRAC methods. The only statistically significant differences between the combinations were observed with the FRAP method. The greatest increase in potential was observed after use of 5-ISA (approx. 17.5%), while a lower increase was observed for KI (approx. 9.0%). The increase in activity after the use of 3,5-diISA was not statistically significant.

In this study, the lack of an increase in oxidative potential in response to the treatments applied can be attributed to the lack of stress, which potentially could be induced in plants by poorly selected concentrations of iodine compounds.