Abstract:A partial block freeze-concentration apparatus (50 L) was applied to concentrate apple vinegar in a pilot study, and the aromatic composition changes in the vinegar and ice samples before and after the concentration process were compared using gas chromatography-mass spectrometry (GC/MS). During this process, the refrigerant interlayer temperature and stirring rate of the freeze concentrator at the beginning stage were controlled at -12.0 ℃ and 300 r/min, respectively. When the ice on the inside wall of the crystallizing tank reached a thickness of 0.50 cm, the refrigerant interlayer temperature and stirring rate were changed to -16.0 ℃ and 500 r/min, respectively, which were maintained until the end of the concentration process. After 11 h, 21.70 kg of concentrated apple vinegar with 9.50% content and 27.84 kg block ice with 0.66% entrainment could be obtained from the initial 50.00 kg apple vinegar. The concentration index and solute yield were 2.13 and 92.24%, respectively. The total loss of aromatic compounds from the block ice was just 3.12%, and the loss rates of characteristic components, such as benzaldehyde, octanoic acid, 4-ethylbenzoic acid butan-2-yl ester, phenylethyl alcohol, and acetic acid 2-phenylethyl ester, were in the range of 3.33~7.47%. However, when the recovery liquid from thawed ice was re-concentrated using similar two-step controlling parameters, the main components recovered were the solutes (e.g. organic acids), but no significant concentration effect was observed in the trace amounts of residual aromatic components.
