Zinc in soybeans. Chemical nature and bioavailability
Abstract
The chemical form and bioavailability of zinc from soybeans was investigated. Soybeans were grown hydroponically and intrinsically labeled with $\sp{65}$Zn through root absorption, stem injection and foliar application. Stem injection resulted in the greatest accumulation of $\sp{65}$Zn. Regardless of the labeling technique, approximately 40-45% of the seed $\sp{65}$Zn was associated with the subcellular organelles. The pattern of $\sp{65}$Zn incorporation into soybeans did not change appreciably as a result of the labeling technique. The major portion of the soluble $\sp{65}$Zn was either free or associated with very low molecular weight proteins, peptides, or their complexes with phytic acid rather than the major proteins of soybeans. Zinc in soybeans is ionically bound to proteins, peptides and phytic acid. Autoclaving did not affect the chemical association of zinc with soy proteins. Solubility of protein, zinc ($\sp{65}$Zn) and phytic acid was studied over the pH range of 3.5-12.0. Solubility of proteins increased with pH. Solubility of phytic acid increased with pH to a maximum at pH 7.5 and then declined to a minimum at pH 12.0. The maximum protein-zinc-phytic acid complex formation was in the pH range of pH 7.7-10.5. Bioavailability of zinc to rats from soybeans was lower than from casein and rats adapted to a casein basal diet absorbed more $\sp{65}$Zn from both casein and soy than rats adapted to a soy basal diet. Retention of $\sp{65}$Zn from either soy or casein test meals decreased with length of adaptation in rats adapted to a casein basal diet as zinc status improved, whereas, $\sp{65}$Zn retention was unchanged with time in rats adapted to soy indicating that adaptation overcame the normal decrease in $\sp{65}$Zn retention with age.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Nutrition
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