Free and Bound Aroma Compounds of Turnjujube (Hovenia acerba Lindl.) during Low Temperature Storage

Free and bound aroma volatiles from turnjujube during low temperature storage were extracted by headspace solid-phase microextraction. They were then characterized and identified using gas chromatography-mass spectrometry. Turnjujube was harvested and stored for 7, 14, and 21 days at 7 °C, the common temperature of display refrigerators in grocery stores. The results showed that 41 free and 24 bound aroma compounds were detected for the first time in turnjujube in both freshly harvested and stored turnjujube. The free and bound aroma compounds of turnjujube were markedly influenced by the storage time. The major free aroma compounds in turnjujube included esters, alcohols, aliphatic aldehydes, and aliphatic ketones. The major bound aroma compounds included borneol, eugenol, and isoeugenol, which contributed to sweet, floral, and herbaceous aroma after their hydrolysis. Freshly harvested turnjujube mostly had a fruity and herbaceous aroma, which diminished after storage at 7 °C. In contrast, the fatty aroma enhanced gradually over storage, and the floral aroma enhanced noticeably after storage for seven days. Foul odor was not detected even after storage at 7 °C for 21 days. The formation mechanisms of some aroma compounds were proposed.