Factors affecting Zymomonas mobilis subsp. francensis growth and acetaldehyde production

An experimental plan was designed to determine the incidence of factors encountered during cider production on Zymomonas mobilis subsp. francensis growth and acetaldehyde production. Different factor combinations of pH (3.50 to 4.10), SO2 addition (0, 50, 100 and 200 mg/L), nitrogen source concentrations (0.5 and 5.0 g/L), polyphenol cider marc extract supplementation (0.25 and 1.00 g/L), temperature (12°C, 18.5°C and 25°C) and inoculation level (102 and 105 CFU/mL) were tested over a 30‐day period at regular time intervals in synthetic medium with ethanol. Viable cell counts and acetaldehyde production were correlated. Individually, and in decreasing significance, the following factors influenced acetaldehyde production: nitrogen source, SO2 addition, inoculation level, temperature and pH. On the other hand, presence of polyphenol cider marc extract was not significant. A model was determined based on factor interactions. At high contamination levels (105 CFU/mL), conditions leading to a high risk for spoilage were observed at pH values ranging from 3.75 to 4.10, at 0 to 50 mg/L total SO2 and in the presence of 5 g/L nitrogen source (yeast extract) while temperature did not in fact appear to play a key role. At lower contamination levels (102 CFU/mL), the risk was drastically reduced. The only conditions leading to increased acetaldehyde levels were a high pH 4.1, no added SO2 and high nitrogen source concentration (5 g/L yeast extract).