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 grow th 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 temperatur e is necessary. At 4 degrees C with an NaCl concentration of 5% and a pH of 7, the tag time was 8 days and no growth was observed at 4 degre es C; with 5% NaCl and a pH of 6. In the absence of salt, P. marginali s could grow regardless of temperature and pH. Pectate lyase and pecti n lyase were produced by P. marginalis, while pectin methyl esterase a ctivity was not observed in our culture conditions. The enzyme product ion depended on temperature, pH, and salt concentration but also on th e age of the culture. Pectinolytic enzymes were abundantly excreted du ring the stationary phase, and even at 4 degrees C, after 2 weeks of s torage, enzyme activities in supernatant culture were sufficient to da mage vegetables. Both bacterial growth and enzymatic production have t o be taken into account in order to estimate correctly the shelf life of vegetables.