Estimation of Iron and Zinc Bioavailability in Salad Formulations with Different Protein Sources

Abstract

A plant-based dietary shift has the potential to reduce the climate impact of the food systems. However, this transition must not compromise the uptake of essential nutrients. Salad bars play a role in this transition, offering customizable and plant rich convenience meals. Despite their popularity, there is limited knowledge regarding the bioavailability of essential minerals in these composed salad meals. This study estimated the bioavailability of iron and zinc in three salad compositions containing different protein sources (meat/fish, lacto-ovo, and plant-based) to determine if they meet the nutritional requirements of school lunches for teenage girls, who are highly susceptible to mineral deficiencies. The salad components were analyzed for phytic acid, iron, and zinc content using high-performance ion chromatography (HPIC) and atomic absorption spectroscopy (AAS). Mineral bioavailability was subsequently estimated using established algorithms (Hallberg and Hulthén, Miller) and molar ratios. The results demonstrate that while the meat-based composition provides highly absorbable iron and zinc, the plant-based and lacto-ovo alternatives fail to meet the absorbable iron requirements for individuals with high physiological needs. This is potentially due to high concentrations of inhibitors such as phytic acid and calcium. Conversely, all salad compositions had high absorption efficiency of zinc. These findings suggest that further optimization is required for salad-based meals to be nutritionally adequate with regard to iron. Potential strategies include substituting meat analogs with fermented products like tempeh, which has a reduced phytic acid content, or utilizing non-soy-based alternatives. Furthermore, mineral bioavailability can be enhanced by moderating the intake of phytate-, calcium-, soy-, and egg-rich components, while increasing the presence of enhancers such as ascorbic acid or animal proteins.