“Framboisé” spoilage in French ciders: Zymomonas mobilis implication and characterization

Biodiversity of 17 Zymomonas mobilis strains isolated from French “framboisé” ciders from 7 different geographical areas of France was analysed using random amplified polymorphic DNA (RAPD) and 6 different strain fingerprints were observed. One of the fingerprints was identical for 10 of the 17 cases. No correlation between geographical origin and strain fingerprint was observed. In parallel, the cider-making process was followed from the orchard to the final product for Z. mobilis presence. Detection of the bacterium only occurred during the fermentation process. The French isolate, strain AN0101, recently proposed as a novel subspecies (Z. mobilis subsp. francensis) was characterized in a synthetic medium using various growth conditions that can be encountered during cider-making (T (°C), pH, ethanol, SO2, polyphenols) to determine growth limits. Results clearly showed that cider is in a risk zone for Z. mobilis contamination as this bacterium was able to grow at temperatures as low as 4 °C, in pH range from 3.5 to 6.0, in 0–8 ml/100 ml ethanol, at the legal limit of 200 mg/l SO2 and in the presence of a cider marc polyphenol extract up to 3 g/l. These results should allow for a better understanding of Z. mobilis conditions of contamination in cider and lead to possible preventive measures in the future.