Abstract: This study aimed to investigate the effect of Ohmic heating on the volatile compounds of soymilk. Headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) was employed to analyze the volatile compounds of samples. The extraction efficiencies of three types of SPME fibers (100 μm PDMS, 65 μm PDMS/DVB and 50/30 μm DVB/CAR/PDMS) were compared. The optimal conditions were determined for the analysis of volatiles in soymilk samples. To eliminate the influence of thermal effects, the Ohmic heating and the traditional heating process were kept as consistent as possible. The results showed that 65 μm PDMS/DVB fiber had a greater sensitivity to a more diverse range of volatile compounds in soymilk, followed by 50/30 μm DVB/CAR/PDMS and 100 μm PDMS fiber. A total of 35 volatile compounds were identified in soymilk, including 16 aldehydes, 5 alcohols, 10 heterocycles (hexanal, (E)-2-heptenal and 1-octene-3-alcohol), 3 ketones and 1 ester. These volatiles contributed to the characteristic flavor of soymilk. Different heating methods had no considerable effect on the types of volatile compounds but significantly affects the contents of the characteristic aroma compounds (P < 0.05). In comparison with the conventional heating group, the contents of hexanal, 1-octen-3-ol and (E)-2-octenal were decreased by 45.55%, 58.60%, and 25.56%, respectively, in the Ohmic heating group. (E)-2-heptenal and 1-hexanol, the major odor compounds of soymilk, were not detected in the Ohmic heating group. Thus, it was concluded that the contents of beany flavor compounds in soymilk could be reduced significantly by Ohmic heating. This research can provide a theoretical basis for the application of Ohmic heating in soymilk processing.

Key words: soymilk, flavor compounds, Ohmic heating, solid-phase microextraction, gas chromatography-mass spectrometry (GC-MS)