Analysis of Microbiological Indicators of Raw Milk Using Chemical Gas Sensors

Introduction: Milk is a complex mixture of fats, proteins, carbohydrates, vitamins and minerals in an accessible form, due to which both native and pathogen microorganisms can rapidly grow in it. Therefore, the development of rapid methods for assessing the microbiological parameters of milk and dairy products is an important task.

Purpose: comparative evaluation of microbiological and physicochemical indicators of raw milk with the results of gas phase analysis over it using an array of chemical gas sensors to develop an express method for determination of its safety.

Materials and methods: The experiment was carried out with samples of raw milk obtained in several farms from cows of various breeds. Standard physicochemical indicators were determined according to GOST (fat, protein, dry solids amount, titratable acidity) and microbiological indicators (QMAFAnM, yeast and mold concentration) by inoculation on nutrient media, as well as identification of microorganisms grown on them using Sanger sequencing with bioinformatics analysis. The gas phase of milk samples was analyzed using piezoelectric quartz sensors with composite coatings in a static sorption mode with signal processing by the principal component analysis.

Results: Physico-chemical and microbiological parameters of raw milk samples were determined, and microorganisms and the microflora phase of milk from each farm were identified. Based on the results of preliminary testing of the sensors in vapors of volatile compounds, it was established that they are characterized by high sensitivity and varying selectivity to substances emitted by microflora of raw milk samples. A comparison of sensor signals and standard indicators was carried out. It is shown that the samples differ in the shape of their “visual prints,” which corresponds to changes in the physicochemical and microbiological indicators of milk samples.

Conclusion: An assessment of the relationship between the results of the gas phase analysis of milk samples and their microbiological indicators using the principal component analysis allowed to establish that using an array of chemical sensors it is possible to separate milk samples with different levels of bacterial contamination. It reduces microbiological analysis time by replacing routine methods.

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