Effect of Environment and Year on the Relationships Between Tofu Texture and Chemical Composition of Soybean in Southern United States

Genotype and environmental factors (location and planting year) affect the food quality of soybeans. This study's objective was to explore the impact of genotype, location, and year on seed components and to identify the correlations between seed components and the firmness of tofu. Seventeen soybean genotypes were grown in replicated field trials in Mississippi, Virginia, and Missouri in 2017 and 2018. Tofu was made from soybean by filled and pressed methods. The major storage proteins' subunit composition, protein's secondary structures, phytic acid content, and Ca²⁺ and Mg²⁺ contents were determined. Results showed both environmental factors, which varied over years and locations, and genotypes had significant interactions ("year × location × genotype," p ≤ 0.001) on seed components. Overall 2-year data demonstrated that the A₃ polypeptide quantitatively correlated with filled tofu firmness (FF) (r = 0.82, p ≤ 0.001) and with pressed tofu firmness (r = 0.83, p ≤ 0.001). In addition, overall data demonstrated that β-secondary structures (β-sheet + β-turn) positively correlated with the pressed and FF with r = 0.89 and 0.88, respectively. Within each trial, the genotype with higher A₃ polypeptide generally produced tofu with higher firmness; for instance, in the 2018 Missouri trial, MS-01 and MS-18 soybeans had 3.54% (high) and 1.93% (low) A₃ with firmness 141.57 (high) and 97 gf/cm² (low), respectively. For applications, A₃ polypeptide and β-secondary structures may be further developed into factors for selecting soybean genotypes for tofu production by the food industry or for breeders to develop new genotypes for improving tofu firmness. PRACTICAL APPLICATIONS: This study investigates the relationships of chemical composition and tofu making of 17 soybean genotypes grown in three locations over 2 years. The results demonstrated that glycinin polypeptide A₃ and β-structures (β-sheet + β-turn) of soybean proteins correlated significantly with tofu firmness. These protein factors can be utilized by both the food industry and plant breeders in their selections of value-added food-grade soybean for tofu quality improvement.