Availability of Zinc in Leavened and Unleavened Wholemeal Wheaten Breads as Measured by Solubility and Uptake by Rat Intestine in vitro

Publisher Website
Google Scholar
Abstract
The availability of zinc in leavened and unleavened wholemeal wheaten breads was examined. Wheat, labeled with 65Zn by injection of label into stems shortly before maturation, was converted into wholemeals of high extraction rate. These were used to prepare yeast-leavened and also unleavened flat breads, the latter being similar to those consumed as the principal dietary staple in rural Iran and nearby countries. The solubility of 65Zn and of stable Zn was two- to threefold greater when leavened bread was suspended in 0.85% NaCl solutions adjusted to pH values between 4.5 and 7.5 than when unleavened bread was so suspended. Uptake of 66Zn by strips of rat jejunum and ileum from suspensions of leavened bread also was significantly greater. The solubility of 66Zn in suspensions of wholemeal bread, either leavened or unleavened, increased exponentially as pH decreased from 7.0 to 4.5. A plot of solubility of 66Zn against pH yielded a relationship closely resembling that described by Kaufman and Kleinberg for titration of phytic acid with calcium hydroxide over this pH range, a finding that was attributed to the interaction of zinc with calcium phytate. It is concluded that fermentation with yeast markedly increases the physiological availability of zinc in wholemeal bread. The gains are attributed in part to the action of yeast in destroying phytate. However, the gain in solubility exceeded by severalfold that to be expected if destruction of phytate was the only cause, so that other changes brought about by fermentation also must contribute.