Estimated Iron and Zinc Bioavailability in Soybean-Maize-Sorghum Ready to Use Foods: Effect of Soy Protein Concentrate and Added Phytase

Akomo PO, Egli I, Okoth MW, Bahwere P, Cercamondi CI, Zeder C, Njage PMK and Owino VO

Efficacy and cost of nutritional supplements are critical in addressing malnutrition. Use of cheaper and locally available ingredients in manufacturing ready-to-use foods (RUF) can potentially reduce cost and increase access to supplements in resource-poor settings. Soy protein concentrate (SPC) is a cheaper source of protein and can potentially replace the more expensive milk powder in RUF. However, SPC contains phytic acid (PA) which inhibits mineral bioavailability. PA may be degraded by the enzyme phytase. This study aimed to determine the effect of replacing skim milk powder (MP) with SPC and of added phytase on bioavailability of iron and zinc in soybean-maize-sorghum RUF.
RUF samples were made using either SPC or MP. Phytase was added to food samples with either low (<5%) or high (>50%) moisture prior to estimation of bioavailability of iron and zinc by in vitro dialysability. Compared to samples with MP, SPC-based foods had significantly higher content of PA (0.84 g/100 g vs. 0.57 g/100 g; p<0.001); lower bioavailability of iron (2.79% vs. 4.85%; p<0.001) and lower zinc bioavailability (3.61% vs. 8.69% for zinc; p<0.001). After one hour of incubation at 35°C, 68% of PA in high-moisture foods and 10% of PA in low moisture foods were degraded. The data indicate that replacing MP with SPC in SMS RUF increases PA content with subsequent reduction of bioavailability of iron and zinc. Added phytase significantly reduces PA content in high moisture foods and may potentially remain active in the Stomach where moisture is high. Adding such a phytase could be a promising approach to increase iron and zinc bioavailability from SMS RUFs and provide cheaper locally produced formulations for addressing malnutrition in resource-poor settings.