Texture assessment of semi-solid dairy products by acoustic-mechanical approach

The shelf-life of two industrial-made whipped dessert dairy creams was followed up to 49 days by monitoring the viscosity of the matrix by means of the stress controlled rheometer (SR 5000, Rheometric Scientific), the morphology of the gas phase in the dispersion (image acquisition by means of a stereo-microscope (200 X) and analysis using the Image Pro-plus software) the mechanical characteristics together with the acoustic emission produced by bubbles bursting when the dairy foam is stressed in a back-extrusion test (TA.XT plus Texture Analyser by Stable Micro Systems equipped with the AED Acoustic Envelope Detector). The flavour release during storage was detected by means of an electronic nose. A chemometrical analysis (PCA and RDA classification technique) was finally employed to get the maximum information from the data obtained, with the special aim of showing the usefulness of the acoustic approach in describing the shelf –life of the aerated creams. The creams (47-49% moisture content, and an average 15% fat content) showed a similar initial degree of aeration and differed in the structuring and stabilizers agents used in the recipe and in the flavour profile.The aging of the whipped creams resulted in an increase of the mechanical properties of the products and in a redistribution of the dimensional classes of the gas phase. Three mechanical variables, one acoustic index and one morphological parameter from the image analysis were selected for the chemometric modeling of data. The analysis was successful for the less heavy cream, while, for the second one, the acoustic analysis results were less conclusive The flavour release showed the same trends, and once again confirmed the relationship existing between flavour release and the structure properties in food matrices.