Influence of exogenous iron, calcium, protein and common salt on the bioaccessibility of zinc from cereals and legumes.

We have earlier reported the zinc bioaccessibility from cereals and pulses and documented the influence of heat processing, germination and fermentation on the same. In the present study, we have assessed the influence of exogenous iron and calcium equivalent to their supplemental levels on the bioaccessibility of zinc from food grains that generally are the major components of meal in India. Bioaccessibility measurement was made by a procedure involving equilibrium dialysis during simulated gastrointestinal digestion. Exogenous iron equivalent to therapeutic levels (5mg per 10g of cereal-legume combination) significantly reduced the bioaccessibility of zinc from the food grains tested, the percent reduction being 32.4. Exogenous calcium equivalent to therapeutic levels (83mg per 10g of the cereal-legume combination) also significantly reduced (by 27.4%) the bioaccessibility of zinc from the tested food grains. The negative influence of exogenous iron and calcium was similar in both raw and cooked grains. Such negative influences on the bioaccessibility of zinc were however not seen when exogenous iron and calcium were only moderate (up to four times the intrinsic level). A study of the influence of exogenous protein on the bioaccessibility of zinc from food grains revealed that soy protein isolate added at amounts to result in a total protein content of 20% produced contrasting effects on zinc and iron bioaccessibility from cereals - rice and sorghum. While soy protein had a negative effect on iron bioaccessibility from these food grains, the same produced an enhancing effect on zinc bioaccessibility (an increase of 50% and 90% increase) from raw and cooked grain, respectively). Exogenous sodium chloride (at 5% level) potentiated the positive effect of soy protein on zinc bioaccessibility, and effectively countered its negative effect on iron bioaccessibility. The observed negative influence of supplemental iron and calcium on zinc bioaccessibility suggests that zinc supplementation may be necessary in the Indian context, whenever iron and calcium supplements are taken, to compensate for the reduction in zinc bioaccessibility.

Influence of heat processing on the bioaccessibility of zinc and iron from cereals and pulses consumed in India.

Influence of heat processing on the bioaccessibility of zinc and iron from food grains consumed in India was evaluated. Cereals - rice (Oryza sativa), finger millet (Eleusine coracana), sorghum (Sorghum vulgare), wheat (Triticum aestivum), and maize (Zea mays), and pulses - chickpea (Cicer arietinum) - whole and decorticated, green gram (Phaseolus aureus) - whole and decorticated, decorticated black gram (Phaseolus mungo), decorticated red gram (Cajanus cajan), cowpea (Vigna catjang), and French bean (Phaseolus vulgaris) were examined for zinc and iron bioaccessibility by employing an in vitro dialysability procedure. Both pressure-cooking and microwave heating were tested for their influence on mineral bioaccessibility. Zinc bioaccessibility from food grains was considerably reduced upon pressure-cooking, especially in pulses. Among cereals, pressure-cooking decreased zinc bioaccessibility by 63% and 57% in finger millet and rice, respectively. All the pressure-cooked cereals showed similar percent zinc bioaccessibility with the exception of finger millet. Bioaccessibility of zinc from pulses was generally lower as a result of pressure-cooking or microwave heating. The decrease in bioaccessibility of zinc caused by microwave heating ranged from 11.4% in chickpea (whole) to 63% in cowpea. Decrease in zinc bioaccessibility was 48% in pressure-cooked whole chickpea, 45% and 55% in pressure-cooked or microwave-heated whole green gram, 32% and 22% in pressure-cooked or microwave-heated decorticated green gram, and 45% in microwave-heated black gram. Iron bioaccessibility, on the other hand, was significantly enhanced generally from all the food grains studied upon heat treatment. Thus, heat treatment of grains produced contrasting effect on zinc and iron bioaccessibility.

Influence of food acidulants on bioaccessibility of zinc and iron from selected food grains.

Four common acidulants in Indian dietary, i. e., citric acid, tamarind (Tamarindus indica), amchur (Mangifera indica), and kokum (Garcinia indica) were examined for a possible influence on the bioaccessibility of zinc from selected food grains. Among the four acidulants examined, amchur and citric acid generally enhanced the bioaccessibility of zinc and iron from all the food grains studied. The increase in zinc bioaccessibility produced by citric acid was around 40% in rice and chickpea, while amchur produced around 60% increase from decorticated green gram. This positive influence of acidulants on zinc bioaccessibility from food grains was seen both in the raw and cooked form. Tamarind and kokum, the other two acidulants tested, generally did not have a favourable influence on zinc and iron bioaccessibility. This lack of positive influence of these two acidulants on mineral availability could be attributable to the presence of significant amounts of tannin in them. Citric acid and amchur also generally enhanced the bioaccessibility of iron from these food grains.