Abstract. As in majority of food during storage, the development of CO 2 in headspace of yogurt is mainly the result of contamination and yeast growth. Thitherto, the monitoring of the changes of CO 2 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 CO 2 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 ""Niška mlekara"", AD Niš, 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 CO 2 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 CO 2 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 CO 2 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 CO 2 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 CO 2 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.
is a very active oxidant of many organic components. Notable exception is the packaging of red meat where a large percentage of oxygen is required in order to maintain the redness of the meat [6].Measuring the residual content of oxygen in MAP is an important step in quality and food safety procedures. Presently, the most used methods are invasive, since a minute amount of the gas to be analyzed is extracted from the package by piercing it with a suitable syringe, then the analysis of the oxygen quantity is performed with a polarimetric sensor, as the case of the widely diffused instruments produced by Dansensor, Denmark. Another available method is based on measuring the fluorescence of a target that has been previously put inside the package and interrogated in a noninvasive way by short-wavelength light, as the case of the instruments produced by Nomacorc, Belgium. On a similar line are used specific targets put inside the package and/or integrated with the covering films that have the property of changing color when exposed to a given amount of oxygen for a given time. However, none of these devices are totally non-intrusive because they require some intervention on the package. Indeed, there is then the need to have a completely non-intrusive way of measuring the oxygen content in the packages.Spectroscopic techniques for trace gas measurement are inherently noninvasive because the measure is done by shining light to the target. A number of techniques have been developed for gas detection. The traditional one has been non-dispersive infrared (NDIR) where the transmission is measured at two different wavelength regions, one over an absorbing and the other at non-absorbing bands. More recently, other techniques have emerged such as Fourier transform infrared (FTIR), differential optical absorption spectroscopy (DOAS), laser-induced fluorescence (LIF) and tunable diode laser absorption spectroscopy (TDLAS). An overview of these techniques is given in [7][8][9].Abstract A device for measuring the oxygen concentration inside packages in modified atmosphere working in a completely non-intrusive way has been developed and tested. The device uses tunable diode laser spectroscopy in a geometry similar to a short distance LIDAR: A laser beam is sent through the top film of a food package, and the absorption is measured by detecting the light scattered by the bottom of the container or by a portion of the food herein contained. The device can operate completely in a contactless way from the package, and the distances of absorption both outside and inside the package are measured with a triangulation system. The performances of the device have been tested for various types of containers, and absolute values for the oxygen concentration have been compared with standard albeit destructive measurements.
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