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TABLE 3. Absolute Amount of Iron Absorbed from Soy Sauce at a 40 Per Cent Reference Dose

DISCUSSION

The results of the present study indicate that ferrous sulphate, in the amount of 75 to 100 mg of elemental iron per dl, has a good solubility in soy sauce and does not change the organoleptic characteristics of the product. According to the results of iron absorption measurements, it can be calculated that, given the average consumption of soy sauce in China of 15 to 20 ml per person every day, the use of fortified soy sauce in vegetable meals would result in the absorption of 0.64 to 1.13 mg of iron per day, an amount sufficient to meet the iron requirements of the general population. It can thus be concluded that soy sauce, fortified at the level proposed, could make a significant contribution to the prevention of iron deficiency in China. The amount of iron (1000 mg Fe/dl) we proposed for the fortification of soy sauce is similar to that used by Garby and Areekul (19) in the FeNa EDTA fortification of fish sauce, and by Nadiger et al. (22) to fortify common salt.

Iron absorption from fortified soy sauce can be doubled by adding ascorbic acid. Consumption of soy sauce fortified with iron and ascorbic acid could provide enough iron to meet the special iron needs of menstruating women. This kind of soy sauce could best be used in uncooked foods or foods already cooked in order to avoid destruction of ascorbic acid activity.

The enhancing effect of ascorbic acid on iron absorption observed in this study was lower than reported in the literature (31). This might have been because of the high iron content of the test meal (23 mg), or to the presence of inhibitors in soy sauce.

The iron absorption from iron-fortified soy sauce cooked with a vegetable meal was similar to that from iron-fortified soy sauce alone, when each individual's iron absorption data were recalculated at a reference dose absorption of 40 per cent. The former was 6.27 per cent, and the latter was 7.09 per cent. These results indicate that the vegetable meal containing potatoes, cabbage, green beans, and rice does not have more potent inhibitors than soy sauce has, a fact that is of considerable practical importance.

It is interesting to notice that the iron absorption from unfortified soy sauce was 6.95 per cent, and if we use the reference dose at 40 per cent to recalculate each individual's absorption data, it increases to 10.8 per cent. This indicates that soy sauce inhibits non-haem iron absorption less than other soy products do (32).

TABLE 4. Chemically Determined Nutrient Content and Calculated Caloric Content of Test Meals

TABLE 5. Iron Absorption from a Vegetable Meal Containing Iron-Fortified Soy Sauce and the Effect of Pork and Tea

*P<0.001.

It is well known that meat enhances non-haem iron absorption. The present findings of a marked effect of pork on the iron absorption from a vegetable meal cooked with iron-fortified soy sauce are in good agreement with other reports (9, 33, 34).

TABLE 6. Absolute Amount of Iron Absorbed from Vegetable Meals Containing Iron-Fortified Soy Sauce at a Reference Dose Absorption of 40 Per Cent

Tea is one of the most well-known inhibitors of iron absorption. Reports in the literature (14, 31) have always used black tea. In the present study a green tea, widely used in China was selected. It also had a marked inhibitory effect.

ACKNOWLEDGEMENTS

This work was supported by a grant from the University of Chile. It was directed by Dr. Abraham Stekel. The author is grateful to Fernando Pizarro, Silvia Núñez, Patricia Chadud, Sandra Llaguno, Mirtha Provoste, and Jorge Olavarría for their outstanding technical help and to Adriana Vargas for secretarial assistance. Dr. Tomes Walter gave invaluable advice.

REFERENCES

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