A comparison of methods for the in vitro determination of the effects of tea on iron availability from foods

Abstract

Two in vitro techniques were used to estimate the effect of tea on the availability of iron in semi-synthetic rat diet and in rice. Both methods entailed measurement of soluble iron after simulated digestion in vitro but one (diffusibility technique) also incorporated a dialysis step so that high molecular weight species (>about 12000) were excluded from the estimated bioavailable fraction. In the case of the semi-synthetic diet a feeding trial was carried out to confirm the negative effect of the tea on the iron status of rats after a prolonged feeding period. The diffusibility technique failed to detect the reduction in iron availability caused by the addition of tea leaves to the rat diet. It was concluded that in vitro methods must be used with caution, and the inclusion of a dialysis step in the technique may cause true availability to be seriously underestimated.