Volatile compounds as markers of tofu (soybean curd) freshness during storage.

Volatile compounds in packed and unpacked commercial tofu were extracted by solid phase microextraction fibers and analyzed by gas chromatography-mass spectrometry. The tofu samples were stored at 4 °C for 15 days to measure freshness and quality changes during storage. Totals of 41 and 35 volatile compounds were identified from packed tofu and unpacked tofu, respectively. Peak area ratio (PAR) of hexanal in packed tofu increased from 11.44 (day 0) to 496.30 (day 9) and finally decreased to 11.06 on day 15 of storage. PAR of ethanol and 1-hexanol increased from 5.41 and 0.76 (day 1) to 66.93 (day 9) and 47.46 (day 15), respectively. Changes in these volatiles in unpacked tofu were similar to those in packed tofu. The results show that hexanal, ethanol, and 1-hexanol are characteristic volatile compounds for providing quantitative and qualitative information regarding deterioration of tofu.