Formation and Cumulation of CO2 in the Bottles of the Fermented Milk Drinks

As in majority of food during storage, the development of CO2 in headspace of yogurt is mainly the result of contamination and yeast growth. Thitherto, the monitoring of the changes of CO2 concentration in the yogurt package"s atmosphere can be an indicator of the product quality and safety. The aim of this paper is to determine the accumulation of the CO2 in the headspace of bottles of fermented milk products: yogurt ""Vedro 2.8% milk fat"" and fermented milk drink with probiotics ""FidoBe 0.5% milk fat"", both produced in ""Niska mlekara"", AD Nis, Serbia. To examine these phenomena, the products were incubated at 30 o C and contaminated with yeast at the levels of 1 and 5 CFU/ml. The strain of yeast used for the contamination was isolated from the spoiled yogurt. During the incubation, the CO2 measurements were continuously performed with a device specially constructed for this purpose. The instrument was based on Tunable Diode Laser Absorption Spectroscopy with a Wavelength Modulation Spectroscopy technique. The number of lactic acid bacteria and the number of yeasts were monitored, too. Also the pH value was measured. The content of CO2 in the headspace of contaminated (initial yeast concentration -1 CFU/ml) bottles of yogurt ""Vedro"" slightly increased from the start value to cca 5,0% at the 30th hour of incubation reaching yeast level of cca 4 logCFU/ml. After that, the CO2 content and the number of yeasts increased faster until the 40th h and reached the values of cca. 16% and 6 logCFU/ml, respectively. During the incubation of the contaminated bottles of fermented milk drink ""FidoBe"", the CO2 level slightly increased from the initial cca 1% to cca 5% during 36 h in bottles contaminated with 1 CFU/ml, and after 30 h in the bottles contaminated with 5 CFU/ml. Hereupon, the increase of CO2 content was faster reaching 20% after 40h in experiment with the initial 5 CFU/ml yeasts, and after 48h in experiment with the initial 1 CFU/ml of yeast. During the incubation, the yeast level increased until the final level of 6.0 logCFU/ml.