Zinc and Magnesium Bioavailability From Acid‐precipitated and Neutralized Soybean Protein Products

Abstract

The bioavailability of zinc (Zn) and magnesium (Mg) from soy protein products freeze‐dried at different pH's was investigated. Soy concentrates and isolates were produced by both acid precipitation (acid soy) or acid precipitation with subsequent neutralization to pH 7.0 (neutral soy). The bioavailability studies involved feeding growing rats isonitrogenous and isocaloric diets based on egg white (with added ZnCO3 or MgCO3) or soy product (substituted in egg white diets to provide equivalent Zn or Mg). Linear regression analysis related amount of Zn (or Mg) in diet to: rat growth (zinc studies), log tibia Zn (or Mg), or serum Mg. Experiments I, II, IV, and V compared the availability of endogenous Zn or Mg from these soy products with ZnCO3 or MgCO3. Experiment III measured the effect of the presence of the acid or neutral soy in rat diets upon the availability of supplemental Zn as ZnCO3. Results of experiments I, II, and IV testing the bioavailability of endogenous zinc showed growth for rats on acid soy was equal to growth from ZnCO3 and greater than from neutral soy. Log tibia zinc analysis demonstrated zinc from both acid and neutral soy products to be less available than ZnCO3 Zn added (Experiment III) to either soy product was highly available. Mg (Experiment V) was highly available from all soy products. It was concluded that neutralization of soy products may result in decreased availability of endogenous Zn but not endogenous Mg.

Hydrothermal Cooking Affects Protein Efficiency Ratio and Zinc Bioavailability of Soymilk‐Based Diets in Rats

“…Phytic acid ϫ Ca:Zn molar ratio is considered to be a reliable predictor of zinc bioavailability in processed products (Fordyce et al, 1987;Lonnerdal et al, 1988;Likuski and Forbes, 1965;Zhou et al, 1992). Also, the type of processing of soy products affects zinc bioavailability (Erdman et al, 1980;Erdman and Forbes, 1981;Erdman and Fordyce, 1989). In our experiments, dietary calcium and zinc concentrations were nearly the same for both soy treatment groups, so processing and zinc bioavailability differences would be the only potential factors differentiating the two groups.…”

“…Also, the type of processing of soy products affects zinc bioavailability (Erdman et al, 1980;Erdman and Forbes, 1981;Erdman and Fordyce, 1989). In our experiments, dietary calcium and zinc concentrations were nearly the same for both soy treatment groups, so processing and zinc bioavailability differences would be the only potential factors differentiating the two groups.…”

Protein-Phytate Interaction in Soybeans. Iii. The Effect of Protein-Phytate Complexes on Zinc Bioavailability

“…The bioavailability of zinc from soy protein products has been found to be highly variable (Erdman et al 1980). Reported differences in zinc utilization from soy isolates of the same phytate content 274 C. A. PRATTLEY, ET AL.…”

Protein–phytate interactions in pig and poultry nutrition: a reappraisal

“…For this reason, the preparation of soya protein isolates and concentrates with reduced phytate contents to avoid Zn deficiencies in human infants has been a goal for decades (53) . As discussed by Erdman (54) , protein concentrates with reduced phytate contents can be prepared by exploiting the capacity of phytate to bind protein, which has been demonstrated in soya (55) and rapeseed (56) , and the fate of phytate following the preparation of soya protein concentrates/isolates has been reviewed (57) . In relation to ternary complexes and protein availability, Champagne et al (58) suggested that the protein moiety of ternary complexes is comprised of either amino acids or small peptides and it then follows that the amount of protein bound in ternary complexes in the small intestine may not be sufficient to compromise amino acid digestibility (9) .…”