**5. Conclusions**

The use of rapid methods for the analysis of the composition and falsification of dairy products has significant advantages over traditional chemical methods. These advantages include: high productivity and degree of automation, speed of measurements, minimal sample preparation, as well as the ability to determine a large number of parameters from the data of one experiment. But to create optimal analyzers for modern manufacturers, it is still necessary to solve such issues as the possibility of introducing the sensor into the milk pipeline, where it will have to take into account the complex polydisperse composition of milk and the heterogeneity of the flow. The analysis should be carried out in the shortest possible time, preferably in real time, and most importantly for manufacturers, it should be inexpensive.

Optical spectroscopy is an extremely powerful and versatile tool for the quantitative and qualitative analysis of milk composition. Not only the concentrations of the principal milk constituents (fat, protein, lactose) but somatic cells count, common adulterants, residual amounts of antibiotics and disinfectants, amino acid composition, and even milk species could be estimated by optical spectroscopic techniques.

Recent advances in chemometrics made possible more widespread use of NIR spectroscopy which allows developing and implementing spectral equipment for on-site or in-line monitoring of milk quality in real-time.

Optical methods are capable of detecting many types of milk adulteration, but not all of them; using optical spectroscopy in combination with other approaches, for example acoustic methods may greatly improve the analytical possibilities of this technique.

Ultrasound techniques are well-developed instruments used for non-destructive, accurate, and non-invasive measurements. Ultrasound spectrometry offers the ability to characterize dairy products excluding special preparation or disruption of the liquid sample. In addition, ultrasound methods are of interest for monitoring processes in real time.

Acoustic measurement techniques can provide data about protein and fat content, size distribution of air and fat droplets, physiochemical changes of milk with time, content of contaminants.

New promising directions for the development of milk characterization can become microfluidic concepts, phononic crystals concepts and a combination of acoustofluidic and optical approaches in one device.

**Author Contributions:** Section 2 was written by A.S.; Section 3 was prepared by G.K. and O.S.; Section 4 was written by N.M. and U.S. Final editing of manuscript was made by A.S. and N.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

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