Formation of 2‐Pentyl Pyridine During Processing of Soybean Protein Isolates as Affected by pH

Levels of 2‐pentyl pyridine (2‐pp) in protein fractions from Stressland soybeans increased to 0.868 ppm (±0.027) at pH 7 after removing insoluble components from defatted flours. If similar protein fractions were held at pH 4.5 or pH 9, the 2‐pp concentration was 0.182 ppm (± 0.003) or 0.199 ppm (± 0.003), respectively. Soybean cultivars KS4694, Edison, and a type null for lipoxygenase 1, 2, and 3 showed similar changes. The increase at pH 7 occurred in less than 1 h. If the defatted flour solution was not subjected to alkaline extraction to remove insoluble components, the increase of 2‐pp at neutral pH did not occur. Thus, the pH conditions should be carefully controlled to produce soybean protein isolates with desired flavor properties.