Volatile aroma components of soy protein isolate and acid-hydrolysed vegetable protein

The volatile aroma components of soy protein isolate (SPI) and acid-hydrolysed vegetable protein (aHVP) were compared by gas chromatography–mass spectrometry (GC–MS) and gas chromatography olfactometry (GCO). Major differences were found between the two soy-based products. Aliphatic aldehydes and ketones were mainly found in SPI, whereas pyrazines and sulphur-containing compounds were dominant in aHVP. Analyses of the non-volatile components showed that SPI was mainly protein (82.5%) with some lipid (3.5%), whereas aHVP contained no protein, only free amino acids (18.4%) and a trace quantity of lipid (0.4%). Polyunsaturates (47.8%), followed by saturates (24.9%) and monounsaturates (14.8%) dominated the fatty acid profile of the SPI lipid fraction. Both SPI and aHVP had a free fatty acid content <0.1%. Sensory analyses of aqueous suspensions of SPI and aHVP demonstrated significant differences in the odours of the two products. Compounds responsible for some of these differences were identified by GCO and GC–MS analyses of aqueous suspensions. The possible role of SPI and aHVP in the development of aroma in extrudates containing these soy products is discussed.