Luminescent Control of Milk Freezing during Transportation and Storage

Optical monitoring improves the efficiency of milk storage and transportation. For instance, optical photoluminescent diagnostics can be used to determine accidental freezing of milk caused by inappropriate storage and transportation. This research featured milk of Michurino brand with 3.2% fat. Its parameters were monitored using an Expert Profi ultrasonic analyzer. The optical diagnostics involved a CM2203 diffraction spectrofluorimeter. After temporary defrosting, the milk quality deteriorated. The spectral characteristics of the previously frozen sample and the control demonstrated quantitative differences in the range of 300–400 nm. Differences also occurred at excitation wavelengths of 324 nm and 360 nm while the excitation wavelengths of 290 nm and 445 nm did not react to freezing. Integral photoluminescence flux Φ324 in the sample subjected to temporary freezing exceeded the same indicator in the unfrozen sample by 12.5% whereas fluxes Φ445 remained almost the same. These differences made it possible to develop an express method for detecting milk freezing. It included excitation with 324 nm (working xcitation) and 445 nm (reference excitation), registration of photoluminescent radiation at 360–600 nm and 480–660 nm, and calculation of the Φ324 vs. Φ445 ratio. The method may be used with LEDs or photodiodes for a non-destructive express monitoring of milk during its storage and transportation in cold regions.