Soybean seed coat properties as determinants of natto and sprout quality

Improving breeding efficiency for superior soybean (Glycine max (L.) Merr.) germplasm used in natto and sprouts requires understanding how seed coat properties relate to quality and functional traits.

We measured seed weight, water uptake, and sprout length and thickness across various genotypes tested at different locations and years. For the 2023-2024 set, we also analyzed fresh sprout weight and the percentage of good sprouts. Seed coat percentage was determined as the seed coat weight relative to the total seed weight. Additionally, we established a robust and reproducible method using scanning electron microscopy (SEM) to directly measure seed coat thickness.

Genotype was the dominant factor influencing nearly all traits, while location, year, and genotype × environment interactions were negligible - except for sprout length in one dataset. Seed coat percentage was unrelated to water uptake but inversely correlated with seed size, and did not consistently predict sprout thickness or length. Importantly, this study is the first to directly measure seed coat thickness and demonstrate its association with water uptake, offering a practical selection criterion for breeding programs targeting natto and sprout quality. SEM imaging further enables detailed analysis of seed coat layers and structural features, opening new opportunities for trait characterization.

By introducing a direct, scalable approach to quantify seed coat traits, this work provides a foundation for more precise breeding strategies and highlights the role of structural seed attributes in improving specialty soybean products. Future research could integrate seed coat thickness into genomic selection models to accelerate breeding progress. © 2026 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.