Characterization of key off-flavor compounds in soybean and their dynamic changes during progressive processing

This study systematically identifies key off-flavor compounds in normal soybean flour (NOR-SF), thereby profiling their dynamic changes among SF-based products manufactured from NOR and high oleic acid (HOA) soybeans. A total of 55 volatile compounds were detected in NOR-SF using headspace solid-phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS), of which 18 were identified as odor-active compounds by GC-O. A total of 13 odorants with odor intensity (AI) ≥ 2 were re-quantified by stable isotope dilution analysis (SIDA), which led to the identification of 10 key odorants with flavor dilution (FD) factors ranging from 4 to 64 and odor activity values (OAVs) > 1. Odor recombination and omission experiments further confirmed their significant contributions to the off-flavor profile of NOR-SF (p < 0.05). Subsequently, a precise SIDA quantification of key off-flavor odorants in eight soybean-based products from two soybean varieties, combined with orthogonal partial least-squares discriminant analysis (OPLS-DA), showed that, except for heptanal, nonanal, and octanal, the concentrations of off-flavor compounds in HOA samples were lower than those in NOR samples. Moreover, the concentrations of off-flavor compounds in soybean meal and soy protein isolate were generally lower than those in soybean flour, except for 2-pentylfuran and 1-hexanol, whereas the concentrations of off-flavor compounds in textured soy protein obtained after extrusion exhibited dynamic fluctuations. These results indicate that the soybean variety significantly affects the formation and evolution of off-flavor compounds in different soybean-based products. This study provides a theoretical basis for controlling off-flavors in products derived from NOR and HOA.