Jainita M Mehta
Nutritional Studies on the Bioavailability of Iron From Cereals and Pulses - Vellanikkara Department of Home Science, College of Horticulture 1998
Nutritional studies to evaluate the bioavailability of iron was conducted
among three selected cereals i.e., rice, wheat and ragi and six pulses i.e., Bengal
gram, green gram, black gram, horse gram, cowpea and soya bean.
The results of the study indicated that among cereals though the total iron
was maximum for ragi but the absolute available iron was less mainly due to its
high fibre and tannin content. Its availability was considerably improved by
germinating ragi for 48 hours when cereals were processed, refined wheat flour had
the maximum iron availability owing to the reduction of fibre and phytic acid
content on refining, while ragi had the least iron availability.
Among pulses the total and absolute available iron was maximum for
bengal gram and soya bean and least for black gram which was found to be high in
phytin phosphorus and tannin content. The total and absolute available iron
increased on dehulling pulses except in the case of soyabean. This increase in iron
was mainly due to the fact that most of the tannins reside in the seed coat of pulses
which are removed on dehulling. A further increase in the iron content was
observed on germinating the pulses due to the break down of antinutritional factors
during germination.
A slight increase in the absolute available iron of fermented and
unfermented idli batter was observed which became more available on cooking by
steaming.
On germinating and roasting ragi almost a four to six fold increase in the
absolute available iron was observed while in pulse the absolute available iron
almost doubled on roasting bengal gram while a ten to fifteen fold increase was
observed in black gram. A further increase in iron was observed on roasting the
pulses after dehulling. Similarly, on frying cereals and pulses only a slight increase
in total and absolute available iron was observed which considerably increased
when pulses were fried after dehulling.
The total iron and absolute available iron was maximum for pressure
cooked rice rather than rice boiled by excess water method. Similar results were
observed when pulses were boiled after soaking due to the leaching of appreciable
quantities of tannins. A further increase in iron content was observed on pressure
cooking the soaked pulses.
The effect of different cooking vessels on the total and absolute available
iron, observed by different cooking and processing methods revealed that the total
iron was maximum for cereals and pulses cooked in iron vessels mainly due to the
contamination of iron from the iron cook ware. The absolute available iron was
maximum for cereals and pulses cooked in inert vessels like glass, mud and tufflon
coated vessels and it was least in the case of aluminium vessels which react with
food constituents forming complex compounds which makes the iron unavailable.
Phytin phosphorus, an inhibitor of iron absorption was noted to reduce on
dehulling and germinating of cereals and pulses thus increasing the absolute
available iron. Among pulses, whole black gram contained the maximum amount of
phytin phosphorus and tannins while green gram contained the least amount of
phytin phosphorus. It was observed that the tannin content in pulses greatly reduced
on dehulling pulses as the tannins are in the seed coat, consequently increasing the
iron availability. When ragi was germinated the tannin content reduced increasing
the total, ionisable and absolute available iron.
On analysing the fibre content of cereals it was observed that whole
wheat flour had the maximum amount of crude fibre which reduced to a minimum
on refining thus increasing the absolute available iron. Similar results were
observed when ragi was germinated where the fibre content reduced with
increasing hours of germination up to 48 hours.
When pulses were dehulled, fibre was seen to reduce greatly
simultaneously increasing the iron availability. On germinating pulses, similar
results were observed up to 48 hours of germination indicating that 48 hours of
germination is adequate for maximum reduction in fibre content.
Pulses do not contain ascorbic acid other than when they are germinated.
Thus with increase in germination time the ascorbic acid is seen to increase
simultaneously increasing the total and absolute available iron. Among the pulses
analysed bengal gram was found to have the highest ascorbic acid content on
germination.
Iron absorption studies from typical Kerala diets revealed that diet III
containing heme iron had the highest ionisable iron while all the diets were high in
iron absorption inhibitors. Modification of the local diets by supplementing or
substituting foods containing iron absorption enhancers or by processing methods
increased the absolute available iron from the diets. Thus by substituting or
supplementing locally available, low cost foods, high in bioavailable iron to rice
based diets would enhance the absolute available iron of our diets.
640 / JAI/NU
Nutritional Studies on the Bioavailability of Iron From Cereals and Pulses - Vellanikkara Department of Home Science, College of Horticulture 1998
Nutritional studies to evaluate the bioavailability of iron was conducted
among three selected cereals i.e., rice, wheat and ragi and six pulses i.e., Bengal
gram, green gram, black gram, horse gram, cowpea and soya bean.
The results of the study indicated that among cereals though the total iron
was maximum for ragi but the absolute available iron was less mainly due to its
high fibre and tannin content. Its availability was considerably improved by
germinating ragi for 48 hours when cereals were processed, refined wheat flour had
the maximum iron availability owing to the reduction of fibre and phytic acid
content on refining, while ragi had the least iron availability.
Among pulses the total and absolute available iron was maximum for
bengal gram and soya bean and least for black gram which was found to be high in
phytin phosphorus and tannin content. The total and absolute available iron
increased on dehulling pulses except in the case of soyabean. This increase in iron
was mainly due to the fact that most of the tannins reside in the seed coat of pulses
which are removed on dehulling. A further increase in the iron content was
observed on germinating the pulses due to the break down of antinutritional factors
during germination.
A slight increase in the absolute available iron of fermented and
unfermented idli batter was observed which became more available on cooking by
steaming.
On germinating and roasting ragi almost a four to six fold increase in the
absolute available iron was observed while in pulse the absolute available iron
almost doubled on roasting bengal gram while a ten to fifteen fold increase was
observed in black gram. A further increase in iron was observed on roasting the
pulses after dehulling. Similarly, on frying cereals and pulses only a slight increase
in total and absolute available iron was observed which considerably increased
when pulses were fried after dehulling.
The total iron and absolute available iron was maximum for pressure
cooked rice rather than rice boiled by excess water method. Similar results were
observed when pulses were boiled after soaking due to the leaching of appreciable
quantities of tannins. A further increase in iron content was observed on pressure
cooking the soaked pulses.
The effect of different cooking vessels on the total and absolute available
iron, observed by different cooking and processing methods revealed that the total
iron was maximum for cereals and pulses cooked in iron vessels mainly due to the
contamination of iron from the iron cook ware. The absolute available iron was
maximum for cereals and pulses cooked in inert vessels like glass, mud and tufflon
coated vessels and it was least in the case of aluminium vessels which react with
food constituents forming complex compounds which makes the iron unavailable.
Phytin phosphorus, an inhibitor of iron absorption was noted to reduce on
dehulling and germinating of cereals and pulses thus increasing the absolute
available iron. Among pulses, whole black gram contained the maximum amount of
phytin phosphorus and tannins while green gram contained the least amount of
phytin phosphorus. It was observed that the tannin content in pulses greatly reduced
on dehulling pulses as the tannins are in the seed coat, consequently increasing the
iron availability. When ragi was germinated the tannin content reduced increasing
the total, ionisable and absolute available iron.
On analysing the fibre content of cereals it was observed that whole
wheat flour had the maximum amount of crude fibre which reduced to a minimum
on refining thus increasing the absolute available iron. Similar results were
observed when ragi was germinated where the fibre content reduced with
increasing hours of germination up to 48 hours.
When pulses were dehulled, fibre was seen to reduce greatly
simultaneously increasing the iron availability. On germinating pulses, similar
results were observed up to 48 hours of germination indicating that 48 hours of
germination is adequate for maximum reduction in fibre content.
Pulses do not contain ascorbic acid other than when they are germinated.
Thus with increase in germination time the ascorbic acid is seen to increase
simultaneously increasing the total and absolute available iron. Among the pulses
analysed bengal gram was found to have the highest ascorbic acid content on
germination.
Iron absorption studies from typical Kerala diets revealed that diet III
containing heme iron had the highest ionisable iron while all the diets were high in
iron absorption inhibitors. Modification of the local diets by supplementing or
substituting foods containing iron absorption enhancers or by processing methods
increased the absolute available iron from the diets. Thus by substituting or
supplementing locally available, low cost foods, high in bioavailable iron to rice
based diets would enhance the absolute available iron of our diets.
640 / JAI/NU