Enhancing iodine content and fruit quality of pepper (Capsicum annuum L.) through biofortification

- Pepper fruits treated with KI contained significantly more iodine.
- Iodine treated fruits had more ascorbic acid and soluble sugar, less total acidity.
- Increasing Chl-a and antioxidant activities contributed to fruit quality improvement.

Iodine is an essential trace element for human health. Its deficiency in biogeochemical environment affects about two billion people worldwide. Besides universal salt iodization, the biofortification of crops with iodine has been proposed as a strategy for improving human nutrition. This study aims at exploring the effects of iodine biofortification on the fruit quality of the pepper plants. The contents of iodine, ascorbic acid, soluble sugar and total acidity of the pepper fruits grown in solution at various iodide concentration levels were measured. Furthermore, in order to reveal the mechanism of fruit quality change, the variations in Chl-a, malondialdehyde (MDA), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) of the pepper leaves at various growth periods in response to various iodine treatments were determined. The results indicated that the iodine content of the pepper fruits grown in 0.25-5.0 mg L−1 KI solutions can amount to 350-1330 μg kg−1 FW, matching the 150 μg d−1 dietary iodine allowance recommended by WHO. Thus, the pepper can be used as a candidate crop for iodine biofortification. In addition, low-moderate levels (0.25-1.0 mg L−1) of iodine application improved the fruit quality by enhancing the ascorbic acid and soluble sugar contents, and by reducing the total acidity of pepper fruits as well. Generally, after iodine treatments, the Chl-a concentration, and CAT, POD, SOD activities of the pepper leaves increased, while the MDA concentration decreased. The changes in photosynthetic and antioxidant capacities of the plants promoted the improvement of the pepper fruit quality.