Identification of volatile compounds in soymilk using solid-phase microextraction-gas chromatography

Headspace solid-phase microextraction (HS-SPME) gas chromatography was used to analyze volatile compounds in soymilk. The effect of incubation temperature (30–70 °C) and time (5–60 min), sample volume (0.5–5 ml), and type of SPME fiber (65 μm CWAX–DVB, 70 μm PDMS–DVB and 85 μm CAR–PDMS) were studied. All the factors markedly affected sensitivity and selectivity. Among the three fibers tested, the CAR–PDMS fiber had greater sensitivity to a more diverse range of volatile compounds, followed by PDMS–DVB and CWAX–DVB fibers using both soymilk and water with added volatiles as a matrix. SPME optimization conducted using a water matrix with added known soy volatiles, showed the following conditions to be optimal for selectivity and sensitivity: incubation temperature of 40 °C, incubation time of 20 min, and sample volume of 5 ml (for volatile compound concentration of ∼25 ppm). The selected conditions were used for the analysis of volatiles in six commercial soymilk samples. A total of 30 volatile compounds were identified. The results showed significant differences in the total volatiles of the soymilk products. The repeatability of measurements of total volatiles compounds of soymilk was ∼5.4% for four replicate analyses. Similar volatile compounds were present in all the samples analyzed but at different concentrations. The method proposed is simple and can be used to measure both hexanal and/or total volatiles in soymilk samples.