Effects of Heat and Pressure Processing on the Relative Biological Value of Selected Dietary Supplemental Inorganic Iron Salts as Determined by Chick Hemoglobin Repletion Assay

Experiments were conducted to determine the effects of heat and pressure processing (1,055 g/cm2 and 121° for 15 minutes) on the bioavailability of four dietary supplemental inorganic iron salts: ferrous sulfate (FeSO4·7H2O); sodium ferric pyrophosphate (Fe4Na8O35P10); ferric orthophosphate (FePO4·2H2O); and ferric pyrophosphate (Fe4[P2O7]3·9H2O). Day-old male broiler chicks were fed a low-iron dried skim milk, casein, corn meal and corn syrup solids basal diet for 14 days to deplete their iron stores and then fed repletion diets containing 0, 5, 10, 15, or 20 ppm of processed or unprocessed test iron diets or unprocessed ferrous sulfate for days 15 through 28. Relative biological value (RBV) was determined by slope-ratio analysis of supplemental iron intake and change in hemoglobin iron during the repletion period utilizing the unprocessed ferrous sulfate as the standard. Heat and pressure processing resulted in the following increases in RBV: ferrous sulfate, 100% to 106%; sodium ferric pyrophosphate, 14% to 66%; ferric orthophosphate, –10% to 11%; and ferric pyrophosphate, 7% to 90%. Thus, combined heat and pressure treatment resulted in an increased RBV of all ferric iron compounds evaluated. The improvement in RBV of ferric pyrophosphate was the greatest and resulted in an RBV not significantly different from the ferrous sulfate standard. The RBV of sodium ferric pyrophosphate was also substantially increased, however, not as markedly as that of ferric pyrophosphate. Heat and pressure processing did not alter the RBV of ferrous sulfate or ferric orthophosphate. J. Nutr. 108: 1477-1484, 1978.