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.