The growth, survival, and death of Listeria monocytogenes were studied in a synthetic medium as a function of temperature, NaCl content, and amount of liquid smoke, and the findings were validated in smoked fish products. The smoke preservative compound was simulated by adding liquid smoke, and the concentration was expressed as phenol concentration. The growth of L. monocytogenes was limited at a temperature as low as 4 degrees C or at a phenol concentration as high as 20 ppm. The predicted values were obtained using a mathematical model established in liquid medium in a previous study. They accurately fit values observed in L. monocytogenes challenge tests on smoked fish. After 21 days of storage the deviation between the predicted and experimental values was within 0.5 log for 60% of the data. This model may be useful in predicting Listeria contamination in smoked fish. Moreover, this study emphasizes the importance of phenol concentration to control the growth of Listeria spp. in smoked food products.

) and freezing (0 and -5°C) treatments. Growth curves generated were fitted by Gompertz and Baranyi functions. The Baranyi function gave better parameter estimation values than the Gompertz equation which over-estimated the specific growth rate values. Listeria monocytogenes grew at 7°C without a lag phase, except when the sub-culture was performed at 37°C, whereas the specific growth rate was affected by the chilling processes. In fact, L. monocytogenes grew slightly faster at 7°C when a 4°C pre-incubation treatment was applied than with a 7°C pre-incubation treatment. These results suggest that to mimic the processes of contamination in industry, predictive microbiology studies with L. monocytogenes should be performed with organisms cultured at low temperatures.

Pectinatus frisingensis, a Gram‐negative and strictly anaerobic beer spoilage bacterium is sensitive to nisin. An increase in nisin concentration (0 to 1100 IU ml−1) added to the culture medium prolonged the lag phase, and decreased the growth rate of the bacterium. In addition, late exponential cells of P. frisingensis exposed to low concentrations of nisin lost immediately a part of their intracellular K+. Presence of Mg2+ up to 15 mmol l−1 did not protect P. frisingensis from nisin‐induced loss of viability and K+ efflux. Potassium leaks were also measured in P. frisingensis late exponential phase cells exposed to combined effects of nisin addition (100–500 IU ml−1), 10 min mild heat‐treatment (50 °C) or rapid cooling (2 °C), and pH (4·0 and 6·2). Net K+ efflux from both starving and glucose‐metabolizing cells, was more important at pH 6·2, whatever the temperature treatment and nisin addition. Reincubation at 30 °C of P. frisingensis glucose‐metabolizing cells exposed to a preliminary combination of nisin addition and mild heat or cooling down treatment, showed that cells exposed to rapid cooling reaccumulated more K+ than heat‐treated cells, whatever the pH conditions. A combination of nisin and mild heat‐treatment could thus be of interest to prevent P. frisingensis growth in beers.

The genus Pectinatus has been often reported in beer spoilage with off-flavours. The bacteria are strictly anaerobic, Gram-negative rods. Propionate and acetate are the main fermentation products from glucose in the two species belonging to the genus, P. cerevisiiphilus and P. frisingensis. Amino acids routinely present at a high level in beer were not growth substrates for both species, and a significant accumulation of succinate was observed with lactate as growth substrate. Both Pectinatus ssp. showed almost identical fermentation balances on glucose. Growth kinetics of both glucose-grown species were unchanged under a N2, H2 or 20% CO2-containing atmosphere. Combinations of culture medium pH values from pH 3 x 9 to pH 7 x 2, of glucose levels between 5 and 55 mmol l-1, and of lactate concentrations varied from 4 to 40 mmol l-1 demonstrated that biomass and volatile fatty acids production were proportional to glucose concentration for both Pectinatus species. A significant increase of volatile fatty acid production was measured for both species at the lowest pH values with a lactate or a glucose concentration increase. The maximum biomass production was observed at pH 6 x 2 for P. cerevisiiphilus, and between pH 4 x 5 and pH 4 x 9 for P. frisingensis. Glucose and lactate or pH value were dependent with regard to propionate and acetate production in P. frisingensis. On the other hand, the variations of these three parameters were independent with regard to biomass production for both strains, and to volatile fatty acids production for P. cerevisiiphilus. Addition of ethanol to glucose-grown cultures completely inhibited growth at 1 x 3 mol l-1 ethanol for P. cerevisiiphilus, and at 1 x 8 mol l-1 for P. frisingensis.

The genus Pectinatus includes strictly anaerobic Gram‐negative non‐spore‐forming mesophilic bacteria often referred to as beer‐spoilage bacteria. Pectinatus frisingensis was chosen as the reference strain. The organisms were grown in batch cultures under stringent anaerobic conditions in a synthetic medium and with pH regulation. Various glucose and lactate concentrations were used, and a low inoculum reproduced spoilage conditions in bottled beer. Propionate and acetate are the major compounds responsible for the off‐flavour of beer. Gompertz curves were fitted to acid‐biomass production and glucose consumption; thereby the lag‐phase, production rate and final concentrations were derived. Volatile fatty acids production began 19 h after biomass growth. There was no lineareffect of substrate on final concentration of propionate, acetate and biomass. An additive model is proposed for the prediction of bacterial growth and acid production on both glucose and lactate.