Effects of air/nitrogen, temperature and pH on energy-dependent growth and survival of Listeria innocua in continuous culture and water-in-oil emulsions

Growth and maintenance energy demands of Listeria innocua were addressed in a chemically defined medium supplemented with casitone (CDMc) in batch and continuous cultures in response to changes in pH (4·2–6·5), temperature (4–30°C) and atmosphere (air vs nitrogen). The effect of temperature on maximal growth rates of L. innocua could be described by a Ratkowsky-type relation. At 30°C L. innocua preferred aerobic conditions reflected by higher growth rates (>40%). The maximum growth yield was higher in aerobic than in anaerobic conditions (88 g compared with 36 g dry weight per mol glucose) and the maintenance energy [m(e)] was lower in aerobic than in anaerobic conditions (0·2 mmol compared with 1·0 mmo, glucose g −1 dry weight per h). Increase in proton concentration gave a decrease in maximal growth rates in batch culture and an increase in m(e) demands. The lower pH limit for growth was 4·2–4·3. Under anaerobic conditions in glucose-limited continuous culture the ratio of lactic to acetic acid as end-products of glucose breakdown increased with rise in dilution rates coinciding with a drop in yield (Y)/glucose bioconversion factor (K Y ). Under aerobic conditions the main end-product was acetic acid. At the highest dilution rates and low pH, acetoin production occurred further reducing the K Y . At near washout dilution rates at pH 4·8–5·0, lactic acid was the main end-product. The physiological information gained was used as input in the mechanistic Verrips model for growth and survival of micro-organisms in water-in-oil emulsions. These input parameters were able to predict growth potential and the trend in survival potential of L. innocua in water-in-oil emulsion products under optimal conditions and at the lower pH edge of growth (4·25–4·3).