Iodine content in iodized salt in Kandy District, Sri Lanka: Effects of temperature and storage conditions on its stability

The primary source of dietary iodine for the Sri Lankan population is iodized salt. Inadequate consumption of iodine leads to iodine deficiency disorders, and excessive intake causes iodine-induced hyperthyroidism. This study assessed the iodine content in commercially available crystal and powder salt products. It also recorded the effect of temperature and packaging material on the stability of iodine. All salt samples contained iodine in both iodate and iodide forms. Five out of ten tested products had iodine levels ranging from 31.60 ± 1.50 to 42.19 ± 3.48 ppm, which exceeded the maximum recommended level of 30 ppm according to the FAO food regulations for Sri Lanka (2005). The iodine contents of four products ranged from 27.20 ± 1.05 to 30.10 ± 1.72 ppm, falling within the recommended fortification range of 15 – 30 ppm. The mean iodine loss after heating at 95 °C for 30 minutes was 5.0% in powdered salt and 8.7% in crystal salts. However, the effect of temperature on total iodine levels was statistically insignificant (p > 0.05). Iodine retention after seven days of storage in an open glass container was 90.78% in crystal salt and 87.11% in powdered salt. The lowest iodine retention was observed in gunny bags, with values 54.24% and 44.77% in crystal and powdered salt, respectively. Heating had an insignificant effect on iodine content, whereas significant iodine loss occurred during storage in gunny bags.  These findings highlight the importance of adopting appropriate packaging materials to ensure the stability and preservation of iodine in fortified salt.