Microbial Sensor for Estimating Organic Acids in Wine

A microbial sensor based on an oxygen electrode and the microorganism Pseudomonas putida was developed in order to determine fixed acids, such as L-malic acid, succinic acid and L-lactic acid, in wine. The carbon source used in cultivating the microorganism affected the selectivity of the sensor to a great extent. When L-lactic acid was used as the carbon source, the microbial sensor gave a selective response for L-lactic acid. A flow injection analysis (FIA) system for determining L-lactic acid was constructed and applied to commercially available wine samples. The obtained result was comparable to that obtained by the F-kit method. On the other hand, the microbial sensor showed a response for L-malic acid, L-lactic acid, succinic acid and ethanol present in wine when meso-tartaric acid was used in the cultivation. The addition of L-lactic acid (0.05mM) and ethanol (0.01%) into the carrier solution suppressed the response for L-lactic acid and ethanol, and under the conditions the microbial sensor was thus selective for L-malic acid and succinic acid. The sensor responses for wine samples (n=6) were linearly related to the sum of the L-malic acid and succinic acid concentrations determined by HPLC with a correlation coefficient of 0.969.