Mineral availability is modified by tannin and phytate content in sorghum flaked breakfast cereals.

Mineral availability from sorghum grain in some varieties may be low because of the presence of phytates and tannins. However, heat processing of sorghum may lower tannin and phytate levels and thus improve mineral availability. Sorghum has potential in the manufacture of gluten free breakfast cereals, therefore flaked breakfast cereals were manufactured from whole grains of three contrasting sorghum varieties and compared to that manufactured from whole grain wheat. The content of tannin, phytate, minerals (Ca, Fe and Zn), in vitro mineral availability and phytate: mineral molar ratios were determined in the raw whole grain flours and the cooked flaked breakfast cereal. For all grain varieties, the in vitro mineral availability of flaked breakfast cereal was higher than the raw flours, an effect most probably related to the concomitant reduction in tannins and phytate levels after processing. The in vitro mineral availability of the flaked wheat breakfast cereal was significantly higher than that of all sorghum breakfast cereals, with that manufactured from the brown sorghum IS8237C having the lowest value (p≤0.05). Given that the sorghum varieties in this study gave lower mineral availability than wheat, other sorghum varieties now require evaluation to identify those with improved mineral availability.

Effects of Genotype and Growth Temperature on the Contents of Tannin, Phytate and In Vitro Iron Availability of Sorghum Grains.

BACKGROUND: It has been predicted that the global temperature will rise in the future, which means crops including sorghum will likely be grown under higher temperatures, and consequently may affect the nutritional properties. METHODS: The effects of two growth temperatures (OT, day/night 32/21°C; HT 38/21°C) on tannin, phytate, mineral, and in vitro iron availability of raw and cooked grains (as porridge) of six sorghum genotypes were investigated. RESULTS: Tannin content significantly decreased across all sorghum genotypes under high growth temperature (P ≤0.05), while the phytate and mineral contents maintained the same level, increased or decreased significantly, depending on the genotype. The in vitro iron availability in most sorghum genotypes was also significantly reduced under high temperature, except for Ai4, which showed a pronounced increase (P ≤0.05). The cooking process significantly reduced tannin content in all sorghum genotypes (P ≤0.05), while the phytate content and in vitro iron availability were not significantly affected. CONCLUSIONS: This research provides some new information on sorghum grain nutritional properties when grown under predicted future higher temperatures, which could be important for humans where sorghum grains are consumed as staple food.