A survey on acetic acid bacteria levels and volatile acidity on several wines of the Republic of Moldova

Acetic acid bacteria (AAB) are ubiquitous wine spoilage microorganisms causing significant economic damage to winemakers by producing acetic acid which affects organoleptic and physicochemical properties of wine thus decreasing its quality. Considering difficulties in their isolation by traditional microbiological methods, it would be advantageous to detect them at all stages of winemaking and prevent wine spoilage.

In this research, we analyzed wines, musts and grapes of 17 varieties grown in different regions of the Republic of Moldova. The DNA was extracted and analyzed by PCR with home-designed primers to detect Acetobacter aceti and Acetobacter pasteurianus. Volatile acidity was determined in wine by steam distillation/titration.

Only one grape (Rara Neagra) had detectable amounts of AAB (A. paseurianus) at all analyzed stages (grape, must, wine), and this sample had the highest amount of volatile acidity (2.11 g/dm³), exceeding the maximum acceptable limit for red wines of 1,2 g/dm³. In general, A. paseurianus was more common than A. aceti both in musts and wines. Generally, samples with no detectable amounts of AAB in either musts or wine (3 samples) had volatile acidity within the acceptable limits. Wine samples positive for AAB but containing low amounts (Ct value >35) did not have volatile acidity above the acceptable. Samples with wine negative but must positive for AAB had volatile acidity close to the acceptable limit.

This research shows the perspective of PCR diagnostics for predicting the risks of wine spoilage by AAB.