Quality of fresh and stored carrots depending on iodine and nitrogen fertilization

Abstract

Introduction: Iodine is an important mineral nutrient essential for a proper functioning of human and animal organism. Despite current programmes of iodine prophylaxis (mainly based on salt iodization) approximately 30-38% of human population has insufficient iodine intake. Crop plants can become an efficient vector of this element in the food chain. Iodine is not a nutrient for plants. For that reason, in addition to determining the possibility of increasing iodine content in crop plant it is necessary to describe its impact on yield quality. The aim of the study was to analyze the influence of soil fertilization with iodine and nitrogen on the quality of carrot roots and its storage ability.

Methods: In 2008-2010 the field study with carrot cv. 'Kazan F1' was conducted. A differential soil fertilization with iodine (in the form of I(-) or IO3(-)) and nitrogen (as NO3(-) or NH4(+)) was applied in the experiment: (1) control without N and I, (2) KI application without N, (3) KIO3 application without N, (4) KI+Ca(NO3)2, (5) KIO3+Ca(NO3)2, (6) KI+(NH4)2SO4 and (7) KIO3+(NH4)2SO4. The experiment was arranged in a split-plot design. Iodine (in both forms) was applied pre-sowing in a dose of 2 kg I ha(-1). Nitrogen in the form of Ca(NO3)2 and (NH4)2SO4 was introduced pre-sowing and as a top dressing, each dose of 100 kg N ha(-1).

Results and discussion: A diverse, statistically significant influence of tested factors on the activity of free radical-scavenging (DPPH) and the content of: dry matter, glucose, fructose, sucrose, total soluble sugars, soluble solids - Brix %, phenolic compounds, phenylpropanoids, flavonols, anthocyanins and carotenoids was noted in carrot roots directly after the harvest as well as at the end of four-month storage. Iodine applied with relatively high doses of nitrogen decreased the quality of fresh carrot. After storage, opposite relations were noted for tested combinations (with I and N application) with respect to carrot quality when compared to results obtained after the harvest. The lowest storage ability was found for carrot treated with KI without N. Obtained results directly suggest the need for developing individual agronomic rules for iodine biofortification of carrot for: (a) consumption and/or processing directly after the harvest and (b) long-term storage.

Keywords: Biofortification; Carotenoids; Carrot; DPPH; Iodine; Phenolic compounds; Post-harvest physiology.