Effect of zinc and aluminum ions in breadmaking

Zinc and aluminum ions as chloride or sulfate salts at 50-500 ppm metal ion (flour basis) had no detrimental effect on fermentation of yeast-leavened dough. Increased mixing times (approximate to 10-50%) due to addition of aq ueous solutions of zinc (250-500 ppm) or aluminum (150-250 ppm) ions to a b read formula was overcome by withholding salt until the final mixing stage. Breads made from commercial flours (12.5% protein) containing zinc (250-50 0 ppm) or aluminum (150-250 ppm) ions and no oxidant had improved loaf volu me and crumb grain when compared with control bread, and no off-taste. Addi tionally, breads with added zinc or aluminum had better crumb grains and sl ower firming rates when compared with breads containing optimum L-ascorbic acid (50 ppm) or potassium bromate (20 ppm). Breads made from commercial fl ours (11.1% protein) and three laboratory flours (11.4-13.6% protein) conta ining zinc (250 ppm) or aluminum (150 ppm) ions also had improved loaf volu mes and crumb grains. Zinc or aluminum ions in combination with L-ascorbic acid, but not potassium bromate, had a detrimental effect on bread quality. Scanning electron microscopy of freeze-dried bread doughs revealed that zi nc and aluminum ions enhanced the film-coating property of gluten. One serv ing (one slice, 28 g) of bread made with 250 ppm zinc ion would provide 25% of the adult recommended dietary allowance of zinc.