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 yog urts were monitored over 30 d of storage at 4 degrees C. Sensory chara cteristics of the yogurts were determined during that time by a traine d panel of judges, and consumer panels were used to test acceptability of iron-fortified yogurt. Counts of lactobacillus delbrueckii ssp. bu lgaricus and Streptococcus thermophilus after 1 d of storage in iron-f ortified skim yogurts were 7.0 x 10(8) cfu/ml, which were not signific antly 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. bulgaric us and S. thermophilus, respectively, after 30 d of storage. Fortifyin g yogurt with iron did not support the growth of Pseudomonas flurescen s or Escherichia coli. No significant increases in chemical oxidation, as measured using the thiobarbituric acid assay, were detected as a c onsequence 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 contro l yogurt. There was no increase in metallic, bitter, or other off-flav ors. The consumer panel did not detect any significant differences in the appearance, mouthfeel, flavor, or overall quality between fortifie d and unfortified flavored yogurts. All yogurt samples were Lilied by the consumer panelists, suggesting that yogurt is a suitable vehicle f or iron fortification.