Effects of Temperature, pH, and NaCl on Growth and Pectinolytic Activity of Pseudomonas marginalis.
The interaction of temperature (4, 10, 18, and 30 degrees C), pH (6, 7, and 8), and NaCl (0, 2.5, and 5%) and their effects on specific growth rate, lag phase, and pectinolytic enzymes of Pseudomonas marginalis were evaluated. Response surface methodology was adapted to describe the response of growth parameters to environmental changes. To obtain good conditions of storage, the combined action of salt and temperature is necessary. At 4 degrees C with an NaCl concentration of 5% and a pH of 7, the lag time was 8 days and no growth was observed at 4 degrees C with 5% NaCl and a pH of 6. In the absence of salt, P. marginalis could grow regardless of temperature and pH. Pectate lyase and pectin lyase were produced by P. marginalis, while pectin methyl esterase activity was not observed in our culture conditions. The enzyme production depended on temperature, pH, and salt concentration but also on the age of the culture. Pectinolytic enzymes were abundantly excreted during the stationary phase, and even at 4 degrees C, after 2 weeks of storage, enzyme activities in supernatant culture were sufficient to damage vegetables. Both bacterial growth and enzymatic production have to be taken into account in order to estimate correctly the shelf life of vegetables.
Membré
J M
JM
Laboratoire de Génie des Procédés et de Technologie Alimentaire, Institut National de la Recherche Agronomique, 59651 Villeneuve d'Ascq Cedex, France.
Burlot
P M
PM