Free amino acids, urea and ammonium ion contents for submerged wine vinegar production: influence of loading rate and air-flow rate

The nitrogen source for acetic acid bacteria is important during the vinegar making process. There can be great variation in the final result according to the specific source, the total nitrogen availability and the operational conditions. These bacteria use L-proline, L-leucine and ammonium ion as their main source of nitrogen from white wine. The effect of loading and air-flow rates on the changes in amino acids, urea and ammonium ion contents have been studied for a semi-batch submerged wine vinegar controlled production. Experiments were carried out in a Frings 8L fermenter working in a semi-batch mode. Amino acid contents were determined from their dansyl derivatives on an HPLC furnished with a C18 reversed-phase column. Urea and ammonium ion contents were quantified with an enzymatic kit. Specific nitrogen consumption is given for 25 amino acids and ammonium ion. In addition, profiles for main system variables as well as the three main nitrogen sources (ammonium ion, L-leucine and L-proline) are given. Type of loading and air-flow rates seemed to have a strong impact on the consumption of the nitrogen compounds tested. An increased loading rate and decreased air-flow rate resulted in greater overall consumption of available nitrogen due to different causes. Nitrogen requirement of the bacteria is proportional to the time spent in the acetification process. An acetification procedure involving relatively sudden changes in the fermentation medium may be desirable in order to reduce the formation of urea.