Changes in the Components of Onion Vinegars by Two Stages Fermentation

Changes in components of onion vinegar during two-stage fermentation were investigated. One sample group (A) was prepared with onion juice by extraction and concentration (15 brix), and the other group (B) was prepared using the same method but supplemented with sucrose. Comparison of glucose (4.1%), fructose (4.2%), and sucrose (0.6%) found in A as major sugars with those (3.2, 3.3, and 4.6%, respectively) of B showed a significant difference in sucrose concentration. During alcohol fermentation, S. kluyvery DJ97 consumed these sugars completely. At 36 hr of alcohol fermentation, concentrations of reducing and total sugars decreased to 0.5 and 0.8%, in A, and 0.4 and 0.6%, in B, respectively. No further changes were detected in the concentrations of these sugars thereafter. From 12 hr of fermentation, alcohol concentrations in groups A and B increased markedly, maximizing at 7.0% at 36 hr A and at 8.2% at 48 hr in B, and finally decreased thereafter in both groups. The detected alcohol components were ethanol, acetaldehyde, methanol, n-propyl alcohol, iso-butanol, and iso-amyl acohol. During acetic acid fermentation, the concentration of acetic acid as the major organic also increased significantly in both groups (4,776.72 and 4,894.93 mg% in A amd B, respectively). Other organic acid contents such as malic and succinic acids were higher in A than B. these results indicate that vinegar is better produced in onion extract with no sucrose supplementation based on its organic acid contents.