Manufacture and quality of iron-fortified yogurt

Yogurts (nonfat and low fat) were manufactured and fortified with 10, 20, and 40 mg of iron/kg of yogurt. Growth of starter culture bacteria and nonstarter culture bacteria as well as lipid oxidation of the yogurts were monitored over 30 d of storage at 4 degrees C. Sensory characteristics of the yogurts were determined during that time by a trained panel of judges, and consumer panels were used to test acceptability of iron-fortified yogurt. Counts of Lactobacillus delbrueckii ssp. bulgaricas and Streptococcus thermophilus after 1 d of storage in iron-fortified skim yogurts were 7.0 x 10(8) cfu/ml, which were not significantly different from numbers in unfortified yogurts. Counts decreased to 2.5 x 10(8) and 1.9 x 10(8) cfu/ml for L. delbrueckii ssp. bulgaricus and S. thermophilus, respectively, after 30 d of storage. Fortifying yogurt with iron did not support the growth of Pseudomonas fluorescens or Escherichia coli. No significant increases in chemical oxidation, as measured using the thiobarbituric acid assay, were detected as a consequence of iron fortification. Trained panelists scored all yogurts for oxidized, metallic, bitter, and other off-flavors in the range of "not perceptible" to "very slightly perceptible". Iron-fortified yogurts had slightly higher oxidized flavor scores than did the control yogurt. There was no increase in metallic, bitter, or other off-flavors. The consumer panel did not detect any significant differences in the appearance, mouthfeel, flavor, or overall quality between fortified and unfortified flavored yogurts. All yogurt samples were liked by the consumer panelists, suggesting that yogurt is a suitable vehicle for iron fortification.