Goitrogens in millets: occurrence, impact on product development and mitigation strategies

Goiter is a health disorder characterized by an enlarged thyroid gland, and it has been associated with iodine deficiency, which can be exacerbated by the ingestion of substances that impair iodine uptake (goitrogens). Millets have been associated with thyroid dysfunctions due to presence of goitrogens. Pearl millet (Pennisetum glaucum), finger millet (Eleusine coracana), and fonio (Digitaria exilis Stapf) contain appreciable amounts of goitrogens, thiocyanates and flavonoids, that can obstruct iodine metabolism in the thyroid. The concentration of thiocyanate and C-glycosyl flavones in finger millet ranged from 31 to 43 mg/kg, and from 15 to 541 and up to 350 mg/kg in pearl millet and fonio contain, respectively. This review consolidates growing knowledge about the occurrence, metabolic pathways, and dietary consequences of goitrogens in millets. The biochemical routes through which goitrogens inhibit the thyroid hormone peroxidase are discussed. The interplay of environmental and varietal and agricultural methods on the goitrogenic profile of minor millets is also clarified. The influence of processing on the breakdown of goitrogens is also discussed. The review findings indicate that employing a dual approach, heat and mechanical processing, reduces goitrogenicity in millets; nevertheless, in certain instances, such as fermentation and sprouting were found to have variable effect, with several studies indicating either stable or increased goitrogen levels. The study shows that cooking or boiling and decortication are the most effective methods to reduce goitrogens in millets.