A new manometric method for measuring carbon dioxide production by dairy starter culture: a case of Leuconostoc mesenteroides
This paper describe a technique for carbon dioxide (CO2) measurement based on the displacement of acidifying liquid in burette at constant pressure. It was adapted to allow the growth of Leuconostoc sp. on semi-synthetic media and milk. A highly precise measurement was obtained using the chemical reaction of sodium carbonate with hydrochloric acid. This method has been proven to present an excellent linear response from 0 to 0.895 mM of CO2 with a high sensitivity. With cultures in milk medium, kinetics of CO2 evolved by Leuconostoc mesenteroides subsp. dextranicum L4 were higher than L. mesenteroides subsp. mesenteroides 19D and L. mesenteroides subsp. cremoris Ec195 grown on milk.. The use of L. mesenteroides subsp. dextranicum L4 and their variants Lac(-)Cit(+), Lac(+)Cit(-) and Lac(-)Cit(-) showed that the CO2 production correlated to the substrate utilization. The curve of CO2 measured was close to the amount of CO2 calculated from lactose and citrate used. The CO2 production rate was higher with the parental strain (6.5 mM/ h) than with the variants. The amount of CO2 produced was always close to the theoritical value, and was also correlated to the growth rate and substrates utilization by L. mesenteroides. The volume of CO2 produced by Leuconostoc in milk was highly correlated with the D-lactate production (r = 0.995). This method could be used routinely for the evaluation and the selection of bacteria having potential ability for CO2 production.
Keywords: Leuconostoc sp., CO2 production, lactic acid, milk