Treatment-induced metabolic shifts of soybean seeds through amino acid–zinc biofortification enhances oil quality and micronutrient density

BACKGROUND: Agronomic biofortification offers a practical approach to enhancing the nutritional and functional quality of soybeans (Glycine max L.); however, the combined metabolic effects of zinc (Zn) and amino acids (AAs) on seed composition remain poorly understood. This two-year field study assessed 16 AA × Zn foliar treatment combinations using an integrated analytical approach that includes mineral enrichment, oil content and yield, detailed fatty acid compositional data, lipid-quality indices, multivariate statistics, network modeling, and multi-criteria decision analysis. RESULTS: Combined application of amino acids and zinc significantly increased key nutrients-while maintaining stable levels of calcium and magnesium. Oil content increased by up to 15% and extracted oil mass increased by up to 13% with moderate-input treatments. Fatty acid profiles were consistently altered, with reductions in stearic and oleic acids and notable increases in linoleic (+ 5.9%) and eicosenoic acids (+ 9%), enhancing the unsaturated-to-saturated ratio without harming oxidative stability. Multivariate and compositional analyses revealed strong, reproducible proportional relationships among fatty acids across years, driven by coordinated Zn- and AA-dependent regulation of desaturase pathways. Lipid-health indices showed significant nutritional enhancements, with high-AA × moderate-Zn combinations producing the most cardio-protective lipid profiles. Network analysis identified oleic acid, linoleic acid, zinc, and nitrogen as central hubs linking nutrient status to lipid metabolism, while multi-criteria rankings showed that treatments using moderate-to-high doses of amino acids combined with moderate-to-high levels of zinc were generally among the best-performing options across ranking methods. CONCLUSIONS: Overall, coordinated foliar application of amino acids and zinc offers a synergistic, environmentally friendly strategy to boost soybean nutrient density, improve oil yield, and promote a healthier lipid profile. The findings support amino acid-zinc biofortification as an efficient and eco-friendly approach for nutrition-focused soybean production.